Skip to main content
NCBI home page
NIHPA Author Manuscripts logoLink to NIHPA Author Manuscripts
. Author manuscript; available in PMC: 2016 Sep 24.
Published in final edited form as: Brain Res. 2014 Oct 5;1621:260–269. doi: 10.1016/j.brainres.2014.09.062

Cerebellar learning mechanisms

John H Freeman 1
PMCID: PMC4385749  NIHMSID: NIHMS633416  PMID: 25289586

Abstract

The mechanisms underlying cerebellar learning are reviewed with an emphasis on old arguments and new perspectives on eyeblink conditioning. Eyeblink conditioning has been used for decades a model system for elucidating cerebellar learning mechanisms. The standard model of the mechanisms underlying eyeblink conditioning is that there two synaptic plasticity processes within the cerebellum that are necessary for acquisition of the conditioned response: 1) long-term depression (LTD) at parallel fiber-Purkinje cell synapses and 2) long-term potentiation (LTP) at mossy fiber-interpositus nucleus synapses. Additional Purkinje cell plasticity mechanisms may also contribute to eyeblink conditioning including LTP, excitability, and entrainment of deep nucleus activity. Recent analyses of the sensory input pathways necessary for eyeblink conditioning indicate that the cerebellum regulates its inputs to facilitate learning and maintain plasticity. Cerebellar learning during eyeblink conditioning is therefore a dynamic interactive process which maximizes responding to significant stimuli and suppresses responding to irrelevant or redundant stimuli.

Keywords: cerebellum, learning, associative learning, plasticity, excitability, eyeblink conditioning

1. Introduction

The cerebellum plays a role in learned adjustments to movement amplitude and timing. The most intensively investigated cerebellar learning paradigms include eyeblink conditioning (J. H. Freeman & Steinmetz, 2011; McCormick & Thompson, 1984a), conditioned limb flexion (Mojtahedian, Kogan, Kanzawa, Thompson, & Lavond, 2007; Voneida, 2000), learned adjustments to load change (Gilbert & Thach, 1977), gaze-reach calibrations (Norris, Hathaway, Taylor, & Thach, 2011), gain and timing modification of the vestibulo-ocular reflex (Boyden, Katoh, & Raymond, 2004; Raymond, Lisberger, & Mauk, 1996a), and learned smooth pursuit eye movements (Medina & Lisberger, 2008). The current review will focus primarily on old arguments and new perspectives on the mechanisms underlying cerebellum-dependent eyeblink conditioning.

2. Early theories of the neural mechanisms underlying cerebellar learning

The mechanisms underlying cerebellar learning were first addressed in computational models by Marr (Marr, 1969) and Albus (Albus, 1971). These models posit that modification in the efficacy of parallel fiber-Purkinje cell synapses is the primary mechanism underlying cerebellar learning. A key component of the Albus (1971) model is that cerebellar Purkinje cells undergo learning-related inhibition. Purkinje cell axonal projections are the sole output of the cerebellar cortex and are exclusively inhibitory. Thus, learning-related inhibition of Purkinje cells releases the cerebellar deep nuclei and vestibular nuclei from inhibition and drives learned. The current interpretation of this inhibitory mechanism is that parallel fiber-Purkinje cell synapses undergo long-term depression (LTD) during learning (Ito & Kano, 1982; Linden, 1994; Linden & Connor, 1991, 1995; Linden, Dickinson, Smeyne, & Connor, 1991). One of the first studies to show an LTD-like mechanism in vivo found decreases in Purkinje cell simple spike activity during a task requiring monkeys to modify wrist movements to compensate for changes in load (Gilbert & Thach, 1977). This demonstration of an LTD-like reduction in Purkinje cell activity is consistent with the Albus model, but it does not prove that the LTD-like mechanism or the cerebellar cortical circuitry is necessary for learning.

3. Neural mechanisms of cerebellar learning in eyeblink conditioning

In the standard delay eyeblink conditioning procedure a conditioned stimulus (CS) that does not elicit eyelid closure before training, typically a tone or light, is followed by an unconditioned stimulus (US) that elicits an eyeblink reflex before training, such as a puff of air to the cornea or a brief shock in the periorbital area (Deaux & Gormezano, 1963; Gormezano, Schneiderman, Deaux, & Fuentes, 1962; Schneiderman, Fuentes, & Gormezano, 1962). Repeated paired presentations of the CS and US result in the development of an “eyeblink” conditioned response (CR) which includes eyelid closure, nictitating membrane movement, and eyeball retraction (Deaux & Gormezano, 1963; Gormezano et al., 1962; Schneiderman et al., 1962). This complex of adaptive responses occurs during the CS with maximum eyelid closure, nictitating membrane movement, and eyeball retraction occurring at the onset of the US (Figure 1). The eyeblink conditioning CR is therefore determined by an association in which the CS predicts the presentation of the US and when it will occur.

Figure 1.

Figure 1

Open in a new tab

Diagram of eye-blink conditioning procedure and timing of the conditioned response. At the start of training an unconditioned response (eyelid closure) occurs after the onset of the unconditioned stimulus (US). With repeated presentations of the conditioned stimulus (CS) and the US a conditioned eyelid closure starts before the onset of the US.

3.1 Essential role of the cerebellum in eyeblink conditioning

Richard Thompson and his colleagues were the first to show that the cerebellum is necessary for eyeblink conditioning (McCormick, Clark, Lavond, & Thompson, 1982). They found that lesions of the cerebellum ipsilateral to the conditioned eye block acquisition and abolish retention of eyeblink conditioning (Lincoln, McCormick, & Thompson, 1982; McCormick et al., 1982; McCormick & Thompson, 1984a). Conditioning of the contralateral eye is completely intact following ipsilateral cerebellar lesions. Subsequent studies found that lesions localized to the dorsolateral anterior interpositus nucleus and medial dentate nucleus abolish eyeblink CRs (G. A. Clark, McCormick, Lavond, & Thompson, 1984; Lavond, Hembree, & Thompson, 1985; Yeo, Hardiman, & Glickstein, 1985). The lesion studies showed that the cerebellum is necessary for acquisition and retention of eyeblink conditioning, but did not prove that the memory underlying the CR is stored within the cerebellum.

The strongest evidence that the memory underlying eyeblink conditioning is stored within the cerebellum comes from a series of studies that used reversible inactivation methods. Inactivation of the intermediate cerebellum ipsilateral to the conditioned eye results in blockade of acquisition and the rate of learning following cessation of the inactivation is the same as in naïve animals, indicating that no savings was established during training with cerebellar inactivation (Figure 2)(R. E. Clark, Zhang, & Lavond, 1992; J. H. Freeman, Jr., Halverson, & Poremba, 2005; Krupa, Thompson, & Thompson, 1993; Nordholm, Thompson, Dersarkissian, & Thompson, 1993). This is a critical point because inactivation could have suppressed expression of the CR but still allowed associative learning to occur upstream or downstream of the cerebellum. These effects alone are not sufficient to demonstrate that the memory is stored exclusively within the cerebellum. It was necessary to examine the effects of inactivating areas downstream of the cerebellum as well. Inactivation of the contralateral red nucleus or the superior cerebellar peduncle completely block CR expression during eyeblink conditioning, but complete savings is found after the cessation if inactivation (Krupa et al., 1993; Krupa & Thompson, 1995; Krupa, Weng, & Thompson, 1996). Inactivation of the cerebellum therefore blocks memory, whereas inactivation of the superior cerebellar peduncle or red nucleus blocks expression of memory (Figure 2). Another approach has been to examine the effects of cerebellar inactivation after training sessions to assess memory consolidation mechanisms. Yeo and colleagues demonstrated that cerebellar cortical inactivation shortly after each eyeblink conditioning session impaired memory, which was evident by a lack of savings from one training day to the next (Attwell, Cooke, & Yeo, 2002; Cooke, Attwell, & Yeo, 2004). This is a particularly important finding because the post-training inactivation effects cannot be attributed to deficits in sensory or motor function during eyeblink conditioning. Evidence that the memory underlying eyeblink conditioning is stored within the cerebellum also comes from numerous studies of cerebellar plasticity mechanisms, as discussed below.

Figure 2.

Figure 2

Open in a new tab

Diagram summarizing the effects of reversible inactivation on different parts of the neural circuitry necessary for eyeblink conditioning. Reversible inactivation of the cerebellum blocks conditional responses (CRs) during acquisition and results in no savings. In contrast, reversible inactivation of the red nucleus (RN), superior cerebellar peduncle (SCP), or motor nuclei (MN) that generate eyelid movement block CRs during acquisition but result in complete savings after inactivation is terminated. The findings indicate that the cerebellum is the primary site of memory storage and the SCP, RN, and MN are necessary for the output necessary to generate the eyelid closure CR.

3.2 Evidence for an LTD-like mechanism at parallel fiber-Purkinje cell synapses during eyeblink conditioning

Neurophysiological studies of Purkinje cell activity during eyeblink conditioning have found learning-related changes in simple spike firing (Berthier & Moore, 1986; Gould & Steinmetz, 1994, 1996; Green & Steinmetz, 2005; Hesslow & Ivarsson, 1994; Jirenhed, Bengtsson, & Hesslow, 2007; Jirenhed & Hesslow, 2011; Katz & Steinmetz, 1997; Nicholson & Freeman, 2004). Pauses in simple spikes develop as eyeblink conditioning progresses, which is consistent with an LTD-like mechanism. The pauses in simple spike activity increase in magnitude during conditioning and decrease during extinction (Jirenhed et al., 2007). These learning-related changes in Purkinje cell simple spike activity suggest that pauses in simple spike firing during the CS release the deep nuclei from tonic inhibition and thereby facilitate CR expression, as would be expected for and LTD-like mechanism (Mauk & Donegan, 1997; Raymond, Lisberger, & Mauk, 1996b).

The feasibility of parallel fiber LTD as a putative mechanism underlying eyeblink conditioning was examined in vitro with forward paired presentations of parallel fiber and climbing fiber stimulation (C. Chen & Thompson, 1995; J. H. Freeman, Jr., Shi, & Schreurs, 1998; Schreurs & Alkon, 1993; Schreurs, Oh, & Alkon, 1996). The cellular and molecular mechanisms underlying Purkinje cell LTD were then examined in vivo. Purkinje cell LTD in vitro is PKC-dependent (J. H. Freeman, Jr., Shi, et al., 1998; Linden & Connor, 1991) and eyeblink conditioning in rabbits is associated with an increase in PKC activation in the molecular layer of the cerebellar cortex (J. H. Freeman, Jr., Scharenberg, Olds, & Schreurs, 1998). LTD at parallel fiber-Purkinje cell synapses is associated with a decrease in AMPA receptors in vitro and a decrease in cerebellar cortical AMPA receptors has been found in rabbits given eyeblink conditioning relative to controls given unpaired presentations of the CS and US or naïve rabbits (Hauge, Tracy, Baudry, & Thompson, 1998). Eyeblink conditioning is also associated with a decrease in excitatory synapses within the outer half of the molecular layer, which are primarily parallel fiber synapses on Purkinje cell dendrites and dendritic spines (Connor et al., 2009). Moreover, genetic manipulations that impair cerebellar cortical LTD generally impair eyeblink conditioning (Aiba et al., 1994; Ichise et al., 2000; Kishimoto et al., 2002; Lee, Chatila, Ram, & Thompson, 2009; Shibuki et al., 1996). The findings from a wide variety of methodological approaches therefore indicate that eyeblink conditioning is associated with an LTD-like mechanism in the cerebellar cortex.

3.3 Evidence for an LTP-like mechanism at mossy fiber-interpositus nucleus synapses during eyeblink conditioning

The release of the deep nuclei from inhibition during pauses in Purkinje cell firing is thought to promote plasticity within the anterior interpositus nucleus (Mauk & Donegan, 1997; Medina & Mauk, 1999; Ohyama, Nores, Medina, Riusech, & Mauk, 2006). In vivo neurophysiological studies have shown that neurons in the anterior interpositus nucleus increase firing during the CS as the CR emerges across training. The burst of interpositus neuronal firing correlates with the amplitude and timing of the CR and precedes it within training trials (Campolattaro, Kashef, Lee, & Freeman, 2011; Choi & Moore, 2003; J. H. Freeman, Jr. & Nicholson, 1999, 2000; Gould & Steinmetz, 1996; Halverson, Lee, & Freeman, 2010). The results of the in vivo neurophysiological studies suggest that the burst of activity in the interpositus nucleus plays a causal role in the production of the CR. Furthermore, electrical stimulation of the anterior interpositus nucleus can elicit eyelid closure before or after eyeblink conditioning, suggesting that the interpositus nucleus can drive the CR through its projections to the red nucleus (J. H. Freeman, Jr. & Nicholson, 2000; McCormick & Thompson, 1984b).

What are the cellular and molecular mechanisms underlying the learning-related bursts of interpositus nucleus activity? Neurons in the deep cerebellar nuclei show increases in intrinsic excitability and EPSPs following stimulation of their excitatory inputs in vitro (Aizenman & Linden, 2000). Synaptic potentiation may be related to an increase in the number or size of mossy fiber-interpositus nucleus excitatory synapses. A quantitative electron microscopy study found that the number of excitatory synapses per neuron within the anterior interpositus nucleus is significantly elevated following 5 days of eyeblink conditioning in rats (Kleim et al., 2002). This finding was replicated by counting mossy fiber varicosities within the anterior interpositus nucleus/dorsolateral hump in mice after 5 days of training (Boele, Koekkoek, De Zeeuw, & Ruigrok, 2013). An increase in the size of excitatory synapses was found within the anterior interpositus nucleus in rabbits following less extensive training (Weeks et al., 2007). Thus, there is an initial increase in the size of excitatory synapses within the anterior interpositus nucleus followed by an increase in synapse number as eyeblink conditioning becomes consolidated. Pharmacological blockade of memory consolidation mechanisms such as protein synthesis, NMDA receptors, and kinase activity within the interpositus nucleus impair eyeblink conditioning, suggesting that these molecular processes may play a role in the learning-related enhancement of mossy fiber-interpositus synaptic function (Bracha et al., 1998; G. Chen & Steinmetz, 2000a, 2000b; Gomi et al., 1999). The enhancement of mossy fiber-interpositus nucleus synapses coupled with pauses in Purkinje cell activity is thought to produce the burst of activity during the CS that drives the CR.

4. New perspectives on cerebellar plasticity: Purkinje cell excitability and LTP

The standard view of cerebellar learning mechanisms underlying eyeblink conditioning in which paired CS-US presentations result in LTD in parallel fiber-Purkinje cell synapses and LTP at mossy fiber-anterior interpositus nucleus synapses may need updating. The Purkinje cell LTD hypothesis was initially based upon the anatomical and physiological properties of the cerebellar circuitry and subsequently gained support from numerous empirical studies, as detail above. A critical source of evidence for the LTD hypothesis has been the demonstration of pauses in simple spike activity during the CS (Green & Steinmetz, 2005; Jirenhed et al., 2007). Many of the in vivo recording studies have also found Purkinje cells with increases in simple spike activity during the CS (Berthier & Moore, 1986; Gould & Steinmetz, 1996; Green & Steinmetz, 2005; Katz & Steinmetz, 1997; Nicholson & Freeman, 2004). This enhancement of simple spike firing has typically been dismissed as reflecting interneuron activity or Purkinje cell activity that is not relevant to the eyeblink CR. An alternative explanation for the Purkinje cells with increased activity is that they may be involved in inhibiting cerebellar output to the levator palpebrae muscle, which raises the upper eyelid. Purkinje cells that increase simple spike activity during the CS increase inhibition of the cerebellar deep nuclei and may thereby decrease excitatory output to motor neurons that activate the levator palpebrae. An elegant study by Delgado-Garcia and colleagues found that different classes of neurons in the interpositus nucleus are excited or inhibited during eyeblink conditioning in cats (Sanchez-Campusano, Gruart, Fernandez-Mas, & Delgado-Garcia, 2012). They found that type-A neurons in the interpositus nucleus increase firing during eyelid closure, whereas type-B neurons fire tonically when the eyelid is open and reduce firing when the eyelid is closing. This antagonistic action of the different types of interpositus neurons is thought to be necessary for the normal kinematic properties of the eyelid closure CR (Sanchez-Campusano et al., 2012). What is the mechanism underlying the pause in type-B neuron activity during eyelid movement? It is proposed here that some of the Purkinje cells that show an increase in simple spike activity during the CS inhibit type-B neurons and thereby reduce excitatory input to the levator palpebrae motor neurons. Thus, Purkinje cells that have pauses vs. increases in simple spike activity work cooperatively to facilitate expression of the CR through the interpositus nucleus (Figure 3).

Figure 3.

Figure 3

Open in a new tab

Diagram depicting how different plasticity mechanisms in Purkinje cells might influence expression of the conditioned response during eyeblink conditioning. Purkinje cells (Pc) that undergo long-term depression (LTD) decrease inhibition of type-A neurons in the interpositus nucleus (A) resulting in stronger excitatory output to the red nucleus (RN) and increased activity in the orbicularis oculi (OO) motor neurons, which causes eyelid closure. Purkinje cells that undergo long-term potentiation (LTP) and/or increases in intrinsic excitability (Excit) increase inhibition of type-B interpositus neurons (B) thereby decreasing excitatory output to the RN and downstream to the levator palpebrae (LP) motor neurons, facilitating eyelid closure. Inhibitory synapses are depicted by a flat ending. All other synapses are excitatory.

What are the mechanisms underlying the increase in Purkinje cell activity during eyeblink conditioning? Increased simple spike activity in these Purkinje cells might be the result of LTP at parallel fiber-Purkinje cell synapses or increased intrinsic excitability. Bernard Schreurs and colleagues were the first to show that eyeblink conditioning results in an increase in Purkinje cell excitability (Schreurs, Gusev, Tomsic, Alkon, & Shi, 1998; Schreurs, Sanchez-Andres, & Alkon, 1991; Schreurs, Tomsic, Gusev, & Alkon, 1997). These authors trained rabbits with eyeblink conditioning and then performed intracellular recordings from cerebellar cortical slices in vitro. Rabbits given paired CS-US training showed an increase in intrinsic excitability in Purkinje cell dendrites, whereas rabbits given unpaired CS and US presentations did not show changes in excitability. The increase in Purkinje cell excitability is caused, at least in part, by inactivation of IA K+ channels (Schreurs et al., 1998). More recent studies have shown that small-conductance Ca2+-activated K+ (SK2) channels are necessary for increased excitability in vitro and facilitate parallel fiber-Purkinje cell LTP (Belmeguenai et al., 2010; Hosy, Piochon, Teuling, Rinaldo, & Hansel, 2011; Ohtsuki, Piochon, Adelman, & Hansel, 2012). Downregulation of SK2 and IA channels as a result of eyeblink conditioning might, therefore, contribute to the facilitated spike firing in some of the Purkinje cells that influence levator palpebrae activity.

Pre-synaptic and post-synaptic LTP have been demonstrated for parallel fiber-Purkinje cell synapses (Hansel, Linden, & D’Angelo, 2001; Jorntell & Hansel, 2006; Salin, Malenka, & Nicoll, 1996). Moreover, reversible plasticity at these synapses has been proposed as crucial for extinction and other aspects of learning (Medina, Nores, & Mauk, 2002). Parallel-fiber LTP also causes increases in intrinsic excitability (Belmeguenai et al., 2010). A recent study found that mice with a Purkinje cell-specific knockout of protein-phosphatase-2B (L7-PP2B) had a severe deficit in LTP but no deficit in LTP in vitro (Schonewille et al., 2010). The L7-PP2B knockout mice were also impaired in acquisition of delay eyeblink conditioning (Schonewille et al., 2010). The findings of this study provide compelling evidence that an LTP-like mechanism at parallel fiber-Purkinje cell synapses may play a substantial role in eyeblink conditioning. This LTP-like mechanism could act on its own or in concert with increased excitability to increase Purkinje cell activity during the CS and inhibit type-B neurons in the anterior interpositus nucleus, thereby reducing input to the downstream levator palpebrae motor neurons during CRs (Figure 3).

It is possible that other types of plasticity mechanisms within the cerebellum (Hansel et al., 2001) play a role in eyeblink conditioning but relatively limited information on this topic is currently available. A more systematic approach examining the effects of genetic and pharmacological manipulations on specific plasticity mechanisms in animals trained on eyeblink conditioning is needed. This kind of systematic approach has been fruitful for examining the plasticity mechanisms underlying various forms of VOR adaptation (Gao, van Beugen, & De Zeeuw, 2012).

5. Purkinje cell entrainment of deep nucleus activity

Another recently discovered property of cerebellar circuitry that may play a role in learning is that deep nucleus neuronal firing can be entrained to synchronously active Purkinje cells (Person & Raman, 2012). In conditions where Purkinje cells are activated synchronously deep nucleus neurons are not tonically inhibited; rather, their activity is entrained to the Purkinje cell activity (Person & Raman, 2012). It is not clear how this property of cerebellar function affects the CR during eyeblink conditioning but it is possible that synchronously activated Purkinje cells, presumably via LTP or increased excitability, might entrain oscillations in interpositus nucleus activity and in turn cause oscillations in the kinematic properties of the CR (Gruart, Schreurs, del Toro, & Delgado-Garcia, 2000). Eyelid CRs show oscillations that differ in frequency across species (Gruart et al., 2000). These oscillations might be driven by synchronously activated Purkinje cells during the CS. The specific oscillation during the CR could be influenced by learning-related plasticity of SK2 channels since their function influences the temporal pattern of Purkinje cell spikes (Belmeguenai et al., 2010; Hosy et al., 2011). Purkinje cells synchronously activated by the CS might therefore play a role in the microstructure of the CR by producing oscillations in type-A neuronal activity as well as inhibiting type-B neurons in the interpositus nucleus during eyeblink conditioning.

6. Cerebellar interactions with the CS and US pathways

The neural pathways that transmit sensory information from the CS and US to the cerebellum during eyeblink conditioning have been identified (J. H. Freeman & Steinmetz, 2011; Mauk, Steinmetz, & Thompson, 1986; J. E. Steinmetz et al., 1987). These pathways are subcortical for delay eyeblink conditioning and provide the inputs necessary for establishing associative plasticity. The cerebellum is not simply a passive recipient of these sensory inputs; it interacts with the CS and US pathways to modulate its own inputs and learning mechanisms (Figure 4).

Figure 4.

Figure 4

Open in a new tab

Diagram depicting interactions between the cerebellum and the conditioned stimulus (CS) and unconditioned stimulus (US) pathways. Purkinje cells (Pc) and neurons in the interpositus nucleus (IP) received input from the CS and US pathways during eyeblink conditioning. As plasticity develops in the cerebellum and the conditioned response starts to be expressed cerebellar output through the interpositus nucleus sends inhibitory feedback to the US pathway at the level of the inferior olive and excitatory feedback to the CS pathway at the level of the pontine nuclei and the medial auditory thalamus. Inhibitory feedback to the inferior olive regulates climbing fiber activity and thereby prevents learning to redundant stimuli and maintains learning-related synaptic plasticity. Excitatory feedback to the CS pathway facilitates conditioning to stimuli that predict the US. Inhibitory synapses are depicted by a flat ending. All other synapses are excitatory.

6.1 The US pathway

Early models of cerebellar learning posited that the climbing fiber axons of the inferior olive could serve as the teaching or error detection input to the cerebellum. The US pathway was subsequently identified by a combination of several experimental approaches. Neuronal activity in the inferior olive or complex spike activity in Purkinje cells is synchronized to US presentations, typically firing 1–3 times following US onset (Jirenhed et al., 2007; Kim, Krupa, & Thompson, 1998; Nicholson & Freeman, 2000, 2003a, 2003b; Rasmussen, Jirenhed, & Hesslow, 2008). Lesions of the inferior olive following eyeblink conditioning cause a decrease in CRs across training trials that parallels extinction, suggesting that the loss of climbing fiber input to the cerebellum is functionally equivalent to omitting the US during extinction training (McCormick, Steinmetz, & Thompson, 1985). A critical experiment for identifying the climbing fiber pathway as the US input to the cerebellum used electrical stimulation of the inferior olive as a US paired with a tone CS (Mauk et al., 1986). This experiment found that stimulation of the inferior olive, if located properly, is sufficient for eyeblink conditioning. These findings and many others indicate that US information is transmitted to the cerebellum via the climbing fiber pathway.

6.2 Cerebellar feedback to the US pathway

The cerebellar nuclei send an inhibitory projection to the inferior olive (Andersson, Garwicz, & Hesslow, 1988; Bengtsson & Hesslow, 2006; Bengtsson, Svensson, & Hesslow, 2004; Hesslow & Ivarsson, 1996; Nicholson & Freeman, 2003a). This inhibitory pathway can be thought of as providing negative feedback, in the context of eyeblink conditioning. Cerebellar inhibitory feedback pathway has been shown to have a progressively stronger effect on the climbing fiber pathway during eyeblink conditioning as bursts of interpositus nucleus activity and the CR develop (Kim et al., 1998; Nicholson & Freeman, 2003a; Sears & Steinmetz, 1991). Learning-related inhibition of the US pathway is important for associative learning because it blocks redundant associations with other stimuli (Kim et al., 1998; Thompson, Thompson, Kim, Krupa, & Shinkman, 1998). Moreover, inhibitory regulation of the US pathway at the level of the inferior olive influences the maintenance of synaptic plasticity in Purkinje cells (Kenyon, Medina, & Mauk, 1998; Medina et al., 2002). Inhibitory feedback from the cerebellum is also necessary for the induction of plasticity mechanisms underlying extinction (Medina et al., 2002).

6.3 The CS pathway

The pontine mossy fiber projection is the most proximal part of the neural pathway that conveys CS input to the cerebellum. Pontine mossy fibers project through the middle cerebellar peduncle to the deep nuclei and the granule cell layer in the cortex. The parallel fiber axons of the granule cells then project to the molecular layer of the cortex. The pontine mossy fiber projection is necessary for eyeblink conditioning with auditory, visual, or tactile CSs (Lewis, Lo Turco, & Solomon, 1987). The auditory pathway is primarily within the lateral and dorsolateral nuclei (Halverson & Freeman, 2010a; J. E. Steinmetz et al., 1987). Lesions or inactivation of the lateral pontine nuclei impair eyeblink conditioning with an auditory CS (Halverson & Freeman, 2010a). Moreover, stimulation of the lateral pontine nuclei is a sufficient CS for eyeblink conditioning (J. H. Freeman, Jr. & Rabinak, 2004; J. H. Freeman, Jr., Rabinak, & Campolattaro, 2005; J. E. Steinmetz, Lavond, & Thompson, 1989; J. E. Steinmetz, Rosen, Chapman, Lavond, & Thompson, 1986; J. E. Steinmetz, Rosen, Woodruff-Pak, Lavond, & Thompson, 1986). Neuronal activity within the lateral pontine nuclei initially shows sensory responses to an auditory CS but then develops learning-related activity during conditioning that is similar to the learning-related activity in the anterior interpositus nucleus (Bao, Chen, & Thompson, 2000; Campolattaro et al., 2011; R. E. Clark, Gohl, & Lavond, 1997; McCormick, Lavond, & Thompson, 1983).

The lateral pontine nuclei receive input from the medial auditory thalamus (Campolattaro, Halverson, & Freeman, 2007; Halverson & Freeman, 2010a). The medial auditory thalamus is necessary for acquisition and retention of eyeblink conditioning with an auditory CS. Like the lateral pontine nuclei, neuronal activity in the medial auditory thalamus initially shows sensory elicited responses but then develops learning-related activity during subsequent training. Stimulation of the medial auditory thalamus is also an effective CS for eyeblink conditioning (Campolattaro et al., 2007). The medial auditory thalamus receives critical input from the inferior colliculus but thalamic input from the cochlear nucleus and superior olive also plays a role in eyeblink conditioning (J. H. Freeman, Halverson, & Hubbard, 2007). CS input is thus transmitted in parallel from brainstem auditory nuclei to the medial auditory thalamus and then to the lateral pontine nuclei.

The visual CS pathway is within the medial pontine nuclei (Halverson & Freeman, 2010b). Inactivation of the medial pontine nuclei severely impairs eyeblink conditioning and stimulation of this pathway is an effective CS (Halverson & Freeman, 2010b; Halverson, Hubbard, & Freeman, 2009). The medial pontine nuclei receive parallel input from the nucleus of the optic tract and ventral division of the lateral geniculate (Halverson & Freeman, 2010b; A. B. Steinmetz, Buss, & Freeman, 2013). The nucleus of the optic tract and ventral lateral geniculate receive direct retinal input. Neurons in the LGNv show learning-related plasticity, but it differs from the plasticity observed in the medial auditory thalamus. LGNv neurons initially show sensory responses to a visual CS and then show maintained responding during eyeblink conditioning relative to control conditions. Thus, the LGNv shows a lack of habituation during eyeblink conditioning rather than facilitation in responding to the CS.

6.4 Cerebellar feedback to the CS pathway

As mentioned above, neurons in the lateral pontine nuclei develop learning-related increases in activity during eyeblink conditioning that resembles the learning-related activity in the anterior interpositus nucleus (Bao et al., 2000; Campolattaro et al., 2011; J. H. Freeman, Jr. & Nicholson, 1999; McCormick et al., 1983). The learning-related activity in the pontine nuclei develops more slowly with training than cerebellar learning-related activity. Inactivation of the interpositus nucleus abolishes this learning-related pontine activity, suggesting that excitatory feedback from the cerebellum is driving the pontine learning-related activity (Bao et al., 2000; R. E. Clark et al., 1997). Medial auditory thalamic neurons also show learning-related activity that develops more slowly than learning-related activity in the anterior interpositus nucleus. The learning-related burst of activity in the medial auditory thalamic nuclei during the CS follows the burst of activity in the anterior interpositus nucleus within training trials (Halverson et al., 2010). These findings suggest that the cerebellum provides excitatory feedback to the medial auditory thalamus that drives the thalamic learning-related activity. A monosynaptic projection from the anterior interpositus nucleus to the medial auditory thalamus was identified, which may be the primary pathway for cerebellar feedback. The CS pathway therefore receives excitatory feedback at the level of the pontine nuclei and the medial auditory thalamus.

The precise role of cerebellar feedback to the CS pathway has not been determined but it is hypothesized that the cerebellum enhances its own input for significant stimuli; in the context of eyeblink conditioning, a significant stimulus is the best predictor of the US (Kim et al., 1998; Thompson et al., 1998). Good stimulus predictors of the US are thus amplified through excitatory feedback to the CS pathway to facilitate cerebellar plasticity, whereas plasticity mechanisms are suppressed for redundant stimuli through inhibitory feedback to the inferior olive (Kim et al., 1998).

7. Summary and Conclusions

Eyeblink conditioning has been studied for decades as a model system, resulting in a wealth of data regarding the neural circuitry and cellular mechanisms underlying associative learning. The standard view of the neural mechanisms underlying eyeblink conditioning is that there are two essential types of synaptic plasticity: 1) an LTD-like mechanism at parallel fiber-Purkinje cell synapses and 2) an LTP-like mechanism at mossy fiber-anterior interpositus nucleus synapses. The LTD-like mechanism causes pauses in Purkinje cell activity during the CS which releases the deep nuclei from tonic inhibition. The release of the anterior interpositus nucleus from Purkinje cell inhibition promotes the development of LTP which, combined with the reduction of Purkinje cell inhibition, causes a burst of firing in projection neurons that then activate the red nucleus and thereby activate motor neurons that produce the eyeblink CR. There is a substantial amount of evidence supporting the standard view but additional plasticity mechanisms might also play role in eyeblink conditioning. Increased Purkinje cell intrinsic excitability and parallel fiber-Purkinje cell LTP might contribute to eyeblink conditioning by suppressing activity of interpositus nucleus neurons that activate the levator palpebrae motor neurons. Purkinje cells with increased activity might also entrain deep nucleus neurons to produce oscillations in eyelid movements. The CS and US pathways that support LTD and LTP within the cerebellum have been identified. These pathways are not simply relays for sensory stimulation; they develop learning-related activity during eyeblink conditioning that is driven by feedback from the cerebellar nuclei. The cerebellum, therefore, regulates its own inputs to facilitate conditioning to stimuli that predict the US and to maintain plasticity when the learning situation has not changed. Tremendous progress has been made toward elucidating the mechanisms underlying eyeblink conditioning and cerebellar learning, but there is still much to be learned. Hypotheses presented in this review regarding the role of facilitated Purkinje cell activity and cerebellar feedback in eyeblink conditioning can only be addressed adequately by continuing the tradition of systematic investigation that was initiated by Thompson and colleagues in the 1970s (Thompson, 1976).

Figure 5.

Figure 5

Open in a new tab

Diagram of the neural circuitry underlying delay eyeblink conditioning. The cerebellar anterior interpositus nucleus (AIN) and Purkinje cells (Pc) in the cerebellar cortex receive convergent input from the conditioned stimulus (CS, green) and unconditioned stimulus (US, red) neural pathways. The CS pathway for an auditory CS includes the cochlear nuclei (CN), superior olive (not shown), lateral lemniscus (not shown), inferior colliculus (IC), medial auditory thalamus (MAT), basilar pontine nuclei (PN), mossy fiber (mf) projection to the AIN and cortical granule cells (Gc), and the parallel fiber (pf) projections to Purkinje cells. The US pathway includes the trigeminal nucleus (TN), dorsal accessory division of the inferior olive (IO), and the climbing fiber (cf) projection to the AIN and Pc. The output pathway for performance of the conditioned blink response (orange) includes the AIN projection to the red nucleus (RN) and its projection to facial motor nucleus (FN) which causes the eyelid closure conditioned response (CR). Feedback projections from the AIN to the PN, MAT, and IO regulate CS and US input to facilitate acquisition and maintain plasticity within the cerebellum. Inhibitory synapses are depicted by a flat ending. All other synapses are excitatory.

Highlights.

  • Eyeblink conditioning is a model system for examining cerebellar learning mechanisms

  • Eyeblink conditioning is mediated by LTD in parallel fiber-Purkinje cell synapses and LTP in mossy fiber-interpositus nucleus synapses

  • Purkinje cell LTP and increased excitability may also contribute to eyeblink conditioning

  • Cerebellar feedback to the CS and US input pathways influences learning and memory

Acknowledgments

This work was supported by NIH grants NS038890 and MH080005 to J.H.F.

Footnotes

Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

References

  1. Aiba A, Kano M, Chen C, Stanton ME, Fox GD, Herrup K, Tonegawa S. Deficient cerebellar long-term depression and impaired motor learning in mGluR1 mutant mice. Cell. 1994;79(2):377–388. [PubMed] [Google Scholar]
  2. Aizenman CD, Linden DJ. Rapid, synaptically driven increases in the intrinsic excitability of cerebellar deep nuclear neurons. Nat Neurosci. 2000;3(2):109–111. doi: 10.1038/72049. [DOI] [PubMed] [Google Scholar]
  3. Albus JS. A theory of cerebellar function. Mathematical Biosciences. 1971;10:25–61. [Google Scholar]
  4. Andersson G, Garwicz M, Hesslow G. Evidence for a GABA-mediated cerebellar inhibition of the inferior olive in the cat. Experimental brain research. 1988;72(3):450. doi: 10.1007/BF00250590. [DOI] [PubMed] [Google Scholar]
  5. Attwell PJ, Cooke SF, Yeo CH. Cerebellar function in consolidation of a motor memory. Neuron. 2002;34(6):1011. doi: 10.1016/s0896-6273(02)00719-5. [DOI] [PubMed] [Google Scholar]
  6. Bao S, Chen L, Thompson RF. Learning- and cerebellum-dependent neuronal activity in the lateral pontine nucleus. Behavioral neuroscience. 2000;114(2):254. doi: 10.1037//0735-7044.114.2.254. [DOI] [PubMed] [Google Scholar]
  7. Belmeguenai A, Hosy E, Bengtsson F, Pedroarena CM, Piochon C, Teuling E, Hansel C. Intrinsic plasticity complements long-term potentiation in parallel fiber input gain control in cerebellar Purkinje cells. J Neurosci. 2010;30(41):13630–13643. doi: 10.1523/JNEUROSCI.3226-10.2010. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Bengtsson F, Hesslow G. Cerebellar control of the inferior olive. Cerebellum. 2006;5(1):7. doi: 10.1080/14734220500462757. [DOI] [PubMed] [Google Scholar]
  9. Bengtsson F, Svensson P, Hesslow G. Feedback control of Purkinje cell activity by the cerebello-olivary pathway. The European journal of neuroscience. 2004;20(11):2999. doi: 10.1111/j.1460-9568.2004.03789.x. [DOI] [PubMed] [Google Scholar]
  10. Berthier NE, Moore JW. Cerebellar Purkinje cell activity related to the classically conditioned nictitating membrane response. Experimental brain research. 1986;63(2):341. doi: 10.1007/BF00236851. [DOI] [PubMed] [Google Scholar]
  11. Boele HJ, Koekkoek SK, De Zeeuw CI, Ruigrok TJ. Axonal sprouting and formation of terminals in the adult cerebellum during associative motor learning. J Neurosci. 2013;33(45):17897–17907. doi: 10.1523/JNEUROSCI.0511-13.2013. [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. Boyden ES, Katoh A, Raymond JL. Cerebellum-dependent learning: the role of multiple plasticity mechanisms. Annual Review of Neuroscience. 2004;27:581–609. doi: 10.1146/annurev.neuro.27.070203.144238. [DOI] [PubMed] [Google Scholar]
  13. Bracha V, Irwin KB, Webster ML, Wunderlich DA, Stachowiak MK, Bloedel JR. Microinjections of anisomycin into the intermediate cerebellum during learning affect the acquisition of classically conditioned responses in the rabbit. Brain Research. 1998;788(1–2):169–178. doi: 10.1016/s0006-8993(97)01535-7. S0006-8993(97)01535-7 [pii] [DOI] [PubMed] [Google Scholar]
  14. Campolattaro MM, Halverson HE, Freeman JH. Medial auditory thalamic stimulation as a conditioned stimulus for eyeblink conditioning in rats. Learning & memory. 2007;14(3):152. doi: 10.1101/lm.465507. [DOI] [PMC free article] [PubMed] [Google Scholar]
  15. Campolattaro MM, Kashef A, Lee I, Freeman JH. Neuronal correlates of cross-modal transfer in the cerebellum and pontine nuclei. The Journal of neuroscience. 2011;31(11):4051. doi: 10.1523/jneurosci.4142-10.2011. [DOI] [PMC free article] [PubMed] [Google Scholar]
  16. Chen C, Thompson RF. Temporal specificity of long-term depression in parallel fiber--Purkinje synapses in rat cerebellar slice. Learning & memory. 1995;2(3–4):185. doi: 10.1101/lm.2.3-4.185. [DOI] [PubMed] [Google Scholar]
  17. Chen G, Steinmetz JE. Intra-cerebellar infusion of NMDA receptor antagonist AP5 disrupts classical eyeblink conditioning in rabbits. Brain Research. 2000a;887(1):144–156. doi: 10.1016/s0006-8993(00)03005-5. S0006-8993(00)03005-5 [pii] [DOI] [PubMed] [Google Scholar]
  18. Chen G, Steinmetz JE. Microinfusion of protein kinase inhibitor H7 into the cerebellum impairs the acquisition but not the retention of classical eyeblink conditioning in rabbits. Brain Research. 2000b;856(1–2):193–201. doi: 10.1016/s0006-8993(99)02429-4. S0006-8993(99)02429-4 [pii] [DOI] [PubMed] [Google Scholar]
  19. Choi JS, Moore JW. Cerebellar neuronal activity expresses the complex topography of conditioned eyeblink responses. Behav Neurosci. 2003;117(6):1211–1219. doi: 10.1037/0735-7044.117.6.1211. [DOI] [PubMed] [Google Scholar]
  20. Clark GA, McCormick DA, Lavond DG, Thompson RF. Effects of lesions of cerebellar nuclei on conditioned behavioral and hippocampal neuronal responses. Brain research. 1984;291(1):125. doi: 10.1016/0006-8993(84)90658-9. [DOI] [PubMed] [Google Scholar]
  21. Clark RE, Gohl EB, Lavond DG. The learning-related activity that develops in the pontine nuclei during classical eye-blink conditioning is dependent on the interpositus nucleus. Learn Mem. 1997;3(6):532–544. doi: 10.1101/lm.3.6.532. [DOI] [PubMed] [Google Scholar]
  22. Clark RE, Zhang AA, Lavond DG. Reversible lesions of the cerebellar interpositus nucleus during acquisition and retention of a classically conditioned behavior. Behavioral neuroscience. 1992;106(6):879. doi: 10.1037//0735-7044.106.6.879. [DOI] [PubMed] [Google Scholar]
  23. Connor S, Bloomfield J, LeBoutillier JC, Thompson RF, Petit TL, Weeks AC. Eyeblink conditioning leads to fewer synapses in the rabbit cerebellar cortex. Behavioral neuroscience. 2009;123(4):856. doi: 10.1037/a0016370. [DOI] [PubMed] [Google Scholar]
  24. Cooke SF, Attwell PJ, Yeo CH. Temporal properties of cerebellar-dependent memory consolidation. The Journal of neuroscience. 2004;24(12):2934. doi: 10.1523/jneurosci.5505-03.2004. [DOI] [PMC free article] [PubMed] [Google Scholar]
  25. Deaux EB, Gormezano I. Eyeball retraction: classical conditioning and extinction in the albino rabbit. Science. 1963;141(3581):630. doi: 10.1126/science.141.3581.630. [DOI] [PubMed] [Google Scholar]
  26. Freeman JH, Halverson HE, Hubbard EM. Inferior colliculus lesions impair eyeblink conditioning in rats. Learning & memory. 2007;14(12):842. doi: 10.1101/lm.716107. [DOI] [PMC free article] [PubMed] [Google Scholar]
  27. Freeman JH, Jr, Halverson HE, Poremba A. Differential effects of cerebellar inactivation on eyeblink conditioned excitation and inhibition. The Journal of neuroscience. 2005;25(4):889. doi: 10.1523/jneurosci.4534-04.2005. [DOI] [PMC free article] [PubMed] [Google Scholar]
  28. Freeman JH, Jr, Nicholson DA. Neuronal activity in the cerebellar interpositus and lateral pontine nuclei during inhibitory classical conditioning of the eyeblink response. Brain research. 1999;833(2):225. doi: 10.1016/s0006-8993(99)01547-4. [DOI] [PubMed] [Google Scholar]
  29. Freeman JH, Jr, Nicholson DA. Developmental changes in eye-blink conditioning and neuronal activity in the cerebellar interpositus nucleus. The Journal of neuroscience. 2000;20(2):813. doi: 10.1523/JNEUROSCI.20-02-00813.2000. [DOI] [PMC free article] [PubMed] [Google Scholar]
  30. Freeman JH, Jr, Rabinak CA. Eyeblink conditioning in rats using pontine stimulation as a conditioned stimulus. Integrative physiological and behavioral science. 2004;39(3):180. doi: 10.1007/bf02734438. [DOI] [PMC free article] [PubMed] [Google Scholar]
  31. Freeman JH, Jr, Rabinak CA, Campolattaro MM. Pontine stimulation overcomes developmental limitations in the neural mechanisms of eyeblink conditioning. Learning & memory. 2005;12(3):255. doi: 10.1101/lm.91105. [DOI] [PMC free article] [PubMed] [Google Scholar]
  32. Freeman JH, Jr, Scharenberg AM, Olds JL, Schreurs BG. Classical conditioning increases membrane-bound protein kinase C in rabbit cerebellum. Neuroreport. 1998;9(11):2669–2673. doi: 10.1097/00001756-199808030-00045. [DOI] [PubMed] [Google Scholar]
  33. Freeman JH, Jr, Shi T, Schreurs BG. Pairing-specific long-term depression prevented by blockade of PKC or intracellular Ca2+ Neuroreport. 1998;9(10):2237. doi: 10.1097/00001756-199807130-00016. [DOI] [PubMed] [Google Scholar]
  34. Freeman JH, Steinmetz AB. Neural circuitry and plasticity mechanisms underlying delay eyeblink conditioning. Learning & memory. 2011;18(10):666. doi: 10.1101/lm.2023011. [DOI] [PMC free article] [PubMed] [Google Scholar]
  35. Gao Z, van Beugen BJ, De Zeeuw CI. Distributed synergistic plasticity and cerebellar learning. Nat Rev Neurosci. 2012;13(9):619–635. doi: 10.1038/nrn3312. [DOI] [PubMed] [Google Scholar]
  36. Gilbert PF, Thach WT. Purkinje cell activity during motor learning. Brain Research. 1977;128(2):309–328. doi: 10.1016/0006-8993(77)90997-0. 0006-8993(77)90997-0 [pii] [DOI] [PubMed] [Google Scholar]
  37. Gomi H, Sun W, Finch CE, Itohara S, Yoshimi K, Thompson RF. Learning induces a CDC2-related protein kinase, KKIAMRE. Journal of Neuroscience. 1999;19(21):9530–9537. doi: 10.1523/JNEUROSCI.19-21-09530.1999. [DOI] [PMC free article] [PubMed] [Google Scholar]
  38. Gormezano I, Schneiderman N, Deaux E, Fuentes I. Nictitating membrane: classical conditioning and extinction in the albino rabbit. Science. 1962;138(3536):33. doi: 10.1126/science.138.3536.33. [DOI] [PubMed] [Google Scholar]
  39. Gould TJ, Steinmetz JE. Multiple-unit activity from rabbit cerebellar cortex and interpositus nucleus during classical discrimination/reversal eyelid conditioning. Brain research. 1994;652(1):98. doi: 10.1016/0006-8993(94)90322-0. [DOI] [PubMed] [Google Scholar]
  40. Gould TJ, Steinmetz JE. Changes in rabbit cerebellar cortical and interpositus nucleus activity during acquisition, extinction, and backward classical eyelid conditioning. Neurobiology of learning and memory. 1996;65(1):17. doi: 10.1006/nlme.1996.0003. [DOI] [PubMed] [Google Scholar]
  41. Green JT, Steinmetz JE. Purkinje cell activity in the cerebellar anterior lobe after rabbit eyeblink conditioning. Learning & memory. 2005;12(3):260. doi: 10.1101/lm.89505. [DOI] [PMC free article] [PubMed] [Google Scholar]
  42. Gruart A, Schreurs BG, del Toro ED, Delgado-Garcia JM. Kinetic and frequency-domain properties of reflex and conditioned eyelid responses in the rabbit. Journal of neurophysiology. 2000;83(2):836. doi: 10.1152/jn.2000.83.2.836. [DOI] [PubMed] [Google Scholar]
  43. Halverson HE, Freeman JH. Medial auditory thalamic input to the lateral pontine nuclei is necessary for auditory eyeblink conditioning. Neurobiology of learning and memory. 2010a;93(1):92. doi: 10.1016/j.nlm.2009.08.008. [DOI] [PMC free article] [PubMed] [Google Scholar]
  44. Halverson HE, Freeman JH. Ventral lateral geniculate input to the medial pons is necessary for visual eyeblink conditioning in rats. Learning & memory. 2010b;17(2):80. doi: 10.1101/lm.1572710. [DOI] [PMC free article] [PubMed] [Google Scholar]
  45. Halverson HE, Hubbard EM, Freeman JH. Stimulation of the lateral geniculate, superior colliculus, or visual cortex is sufficient for eyeblink conditioning in rats. Learning & memory. 2009;16(5):300. doi: 10.1101/lm.1340909. [DOI] [PMC free article] [PubMed] [Google Scholar]
  46. Halverson HE, Lee I, Freeman JH. Associative plasticity in the medial auditory thalamus and cerebellar interpositus nucleus during eyeblink conditioning. The Journal of neuroscience. 2010;30(26):8787. doi: 10.1523/jneurosci.0208-10.2010. [DOI] [PMC free article] [PubMed] [Google Scholar]
  47. Hansel C, Linden DJ, D’Angelo E. Beyond parallel fiber LTD: the diversity of synaptic and non-synaptic plasticity in the cerebellum. Nat Neurosci. 2001;4(5):467–475. doi: 10.1038/87419. [DOI] [PubMed] [Google Scholar]
  48. Hauge SA, Tracy JA, Baudry M, Thompson RF. Selective changes in AMPA receptors in rabbit cerebellum following classical conditioning of the eyelid-nictitating membrane response. Brain research. 1998;803(1–2):9. doi: 10.1016/s0006-8993(98)00525-3. [DOI] [PubMed] [Google Scholar]
  49. Hesslow G, Ivarsson M. Suppression of cerebellar Purkinje cells during conditioned responses in ferrets. Neuroreport. 1994;5(5):649. doi: 10.1097/00001756-199401000-00030. [DOI] [PubMed] [Google Scholar]
  50. Hesslow G, Ivarsson M. Inhibition of the inferior olive during conditioned responses in the decerebrate ferret. Experimental brain research. 1996;110(1):36. doi: 10.1007/BF00241372. [DOI] [PubMed] [Google Scholar]
  51. Hosy E, Piochon C, Teuling E, Rinaldo L, Hansel C. SK2 channel expression and function in cerebellar Purkinje cells. J Physiol. 2011;589(Pt 14):3433–3440. doi: 10.1113/jphysiol.2011.205823. [DOI] [PMC free article] [PubMed] [Google Scholar]
  52. Ichise T, Kano M, Hashimoto K, Yanagihara D, Nakao K, Shigemoto R, Aiba A. mGluR1 in cerebellar Purkinje cells essential for long-term depression, synapse elimination, and motor coordination. Science. 2000;288(5472):1832–1835. doi: 10.1126/science.288.5472.1832. 8574 [pii] [DOI] [PubMed] [Google Scholar]
  53. Ito M, Kano M. Long-lasting depression of parallel fiber-Purkinje cell transmission induced by conjunctive stimulation of parallel fibers and climbing fibers in the cerebellar cortex. Neuroscience Letters. 1982;33(3):253–258. doi: 10.1016/0304-3940(82)90380-9. [DOI] [PubMed] [Google Scholar]
  54. Jirenhed DA, Bengtsson F, Hesslow G. Acquisition, extinction, and reacquisition of a cerebellar cortical memory trace. The Journal of neuroscience. 2007;27(10):2493. doi: 10.1523/jneurosci.4202-06.2007. [DOI] [PMC free article] [PubMed] [Google Scholar]
  55. Jirenhed DA, Hesslow G. Learning stimulus intervals--adaptive timing of conditioned purkinje cell responses. Cerebellum. 2011;10(3):523. doi: 10.1007/s12311-011-0264-3. [DOI] [PubMed] [Google Scholar]
  56. Jorntell H, Hansel C. Synaptic memories upside down: bidirectional plasticity at cerebellar parallel fiber-Purkinje cell synapses. Neuron. 2006;52(2):227–238. doi: 10.1016/j.neuron.2006.09.032. [DOI] [PubMed] [Google Scholar]
  57. Katz DB, Steinmetz JE. Single-unit evidence for eye-blink conditioning in cerebellar cortex is altered, but not eliminated, by interpositus nucleus lesions. Learning & memory. 1997;4(1):88. doi: 10.1101/lm.4.1.88. [DOI] [PubMed] [Google Scholar]
  58. Kenyon GT, Medina JF, Mauk MD. A mathematical model of the cerebellar-olivary system I: self-regulating equilibrium of climbing fiber activity. Journal of computational neuroscience. 1998;5(1):17. doi: 10.1023/a:1008874209991. [DOI] [PubMed] [Google Scholar]
  59. Kim JJ, Krupa DJ, Thompson RF. Inhibitory cerebello-olivary projections and blocking effect in classical conditioning. Science. 1998;279(5350):570. doi: 10.1126/science.279.5350.570. [DOI] [PubMed] [Google Scholar]
  60. Kishimoto Y, Fujimichi R, Araishi K, Kawahara S, Kano M, Aiba A, Kirino Y. mGluR1 in cerebellar Purkinje cells is required for normal association of temporally contiguous stimuli in classical conditioning. European Journal of Neuroscience. 2002;16(12):2416–2424. doi: 10.1046/j.1460-9568.2002.02407.x. 2407 [pii] [DOI] [PubMed] [Google Scholar]
  61. Kleim JA, Freeman JH, Jr, Bruneau R, Nolan BC, Cooper NR, Zook A, Walters D. Synapse formation is associated with memory storage in the cerebellum. Proceedings of the National Academy of Sciences of the United States of America. 2002;99(20):13228–13231. doi: 10.1073/pnas.202483399202483399. [pii] [DOI] [PMC free article] [PubMed] [Google Scholar]
  62. Krupa DJ, Thompson JK, Thompson RF. Localization of a memory trace in the mammalian brain. Science. 1993;260(5110):989. doi: 10.1126/science.8493536. [DOI] [PubMed] [Google Scholar]
  63. Krupa DJ, Thompson RF. Inactivation of the superior cerebellar peduncle blocks expression but not acquisition of the rabbit’s classically conditioned eye-blink response. Proceedings of the National Academy of Sciences of the United States of America. 1995;92(11):5097. doi: 10.1073/pnas.92.11.5097. [DOI] [PMC free article] [PubMed] [Google Scholar]
  64. Krupa DJ, Weng J, Thompson RF. Inactivation of brainstem motor nuclei blocks expression but not acquisition of the rabbit’s classically conditioned eyeblink response. Behavioral neuroscience. 1996;110(2):219. doi: 10.1037//0735-7044.110.2.219. [DOI] [PubMed] [Google Scholar]
  65. Lavond DG, Hembree TL, Thompson RF. Effect of kainic acid lesions of the cerebellar interpositus nucleus on eyelid conditioning in the rabbit. Brain research. 1985;326(1):179. doi: 10.1016/0006-8993(85)91400-3. [DOI] [PubMed] [Google Scholar]
  66. Lee KH, Chatila TA, Ram RA, Thompson RF. Impaired memory of eyeblink conditioning in CaMKIV KO mice. Behavioral neuroscience. 2009;123(2):438. doi: 10.1037/a0014724. [DOI] [PubMed] [Google Scholar]
  67. Lewis JL, Lo Turco JJ, Solomon PR. Lesions of the middle cerebellar peduncle disrupt acquisition and retention of the rabbit’s classically conditioned nictitating membrane response. Behavioral neuroscience. 1987;101(2):151. doi: 10.1037//0735-7044.101.2.151. [DOI] [PubMed] [Google Scholar]
  68. Lincoln JS, McCormick DA, Thompson RF. Ipsilateral cerebellar lesions prevent learning of the classically conditioned nictitating membrane/eyelid response. Brain research. 1982;242(1):190. doi: 10.1016/0006-8993(82)90510-8. [DOI] [PubMed] [Google Scholar]
  69. Linden DJ. Long-term synaptic depression in the mammalian brain. Neuron. 1994;12(3):457–472. doi: 10.1016/0896-6273(94)90205-4. 0896-6273(94)90205-4 [pii] [DOI] [PubMed] [Google Scholar]
  70. Linden DJ, Connor JA. Participation of postsynaptic PKC in cerebellar long-term depression in culture. Science. 1991;254(5038):1656–1659. doi: 10.1126/science.1721243. [DOI] [PubMed] [Google Scholar]
  71. Linden DJ, Connor JA. Long-term synaptic depression. Annual Review of Neuroscience. 1995;18:319–357. doi: 10.1146/annurev.ne.18.030195.001535. [DOI] [PubMed] [Google Scholar]
  72. Linden DJ, Dickinson MH, Smeyne M, Connor JA. A long-term depression of AMPA currents in cultured cerebellar Purkinje neurons. Neuron. 1991;7(1):81–89. doi: 10.1016/0896-6273(91)90076-c. 0896-6273(91)90076-C [pii] [DOI] [PubMed] [Google Scholar]
  73. Marr D. A theory of cerebellar cortex. Journal of Physiology. 1969;202:437–470. doi: 10.1113/jphysiol.1969.sp008820. [DOI] [PMC free article] [PubMed] [Google Scholar]
  74. Mauk MD, Donegan NH. A model of Pavlovian eyelid conditioning based on the synaptic organization of the cerebellum. Learning & memory. 1997;4(1):130. doi: 10.1101/lm.4.1.130. [DOI] [PubMed] [Google Scholar]
  75. Mauk MD, Steinmetz JE, Thompson RF. Classical conditioning using stimulation of the inferior olive as the unconditioned stimulus. Proceedings of the National Academy of Sciences of the United States of America. 1986;83(14):5349. doi: 10.1073/pnas.83.14.5349. [DOI] [PMC free article] [PubMed] [Google Scholar]
  76. McCormick DA, Clark GA, Lavond DG, Thompson RF. Initial localization of the memory trace for a basic form of learning. Proceedings of the National Academy of Sciences of the United States of America. 1982;79(8):2731. doi: 10.1073/pnas.79.8.2731. [DOI] [PMC free article] [PubMed] [Google Scholar]
  77. McCormick DA, Lavond DG, Thompson RF. Neuronal responses of the rabbit brainstem during performance of the classically conditioned nictitating membrane (NM)/eyelid response. Brain research. 1983;271(1):73. doi: 10.1016/0006-8993(83)91366-5. [DOI] [PubMed] [Google Scholar]
  78. McCormick DA, Steinmetz JE, Thompson RF. Lesions of the inferior olivary complex cause extinction of the classically conditioned eyeblink response. Brain research. 1985;359(1–2):120. doi: 10.1016/0006-8993(85)91419-2. [DOI] [PubMed] [Google Scholar]
  79. McCormick DA, Thompson RF. Cerebellum: essential involvement in the classically conditioned eyelid response. Science. 1984a;223(4633):296. doi: 10.1126/science.6701513. [DOI] [PubMed] [Google Scholar]
  80. McCormick DA, Thompson RF. Neuronal responses of the rabbit cerebellum during acquisition and performance of a classically conditioned nictitating membrane-eyelid response. The Journal of neuroscience. 1984b;4(11):2811. doi: 10.1523/JNEUROSCI.04-11-02811.1984. [DOI] [PMC free article] [PubMed] [Google Scholar]
  81. Medina JF, Lisberger SG. Links from complex spikes to local plasticity and motor learning in the cerebellum of awake-behaving monkeys. Nature Neuroscience. 2008;11(10):1185–1192. doi: 10.1038/nn.2197. nn.2197 [pii] [DOI] [PMC free article] [PubMed] [Google Scholar]
  82. Medina JF, Mauk MD. Simulations of cerebellar motor learning: computational analysis of plasticity at the mossy fiber to deep nucleus synapse. The Journal of neuroscience. 1999;19(16):7140. doi: 10.1523/JNEUROSCI.19-16-07140.1999. [DOI] [PMC free article] [PubMed] [Google Scholar]
  83. Medina JF, Nores WL, Mauk MD. Inhibition of climbing fibres is a signal for the extinction of conditioned eyelid responses. Nature. 2002;416(6878):330. doi: 10.1038/416330a. [DOI] [PubMed] [Google Scholar]
  84. Mojtahedian S, Kogan DR, Kanzawa SA, Thompson RF, Lavond DG. Dissociaton of conditioned eye and limb responses in the cerebellar interpositus. Physiology & Behavior. 2007;91(1):9. doi: 10.1016/j.physbeh.2007.01.006. [DOI] [PubMed] [Google Scholar]
  85. Nicholson DA, Freeman JH., Jr Developmental changes in eye-blink conditioning and neuronal activity in the inferior olive. The Journal of neuroscience. 2000;20(21):8218. doi: 10.1523/JNEUROSCI.20-21-08218.2000. [DOI] [PMC free article] [PubMed] [Google Scholar]
  86. Nicholson DA, Freeman JH., Jr Addition of inhibition in the olivocerebellar system and the ontogeny of a motor memory. Nature neuroscience. 2003a;6(5):532. doi: 10.1038/nn1042. [DOI] [PMC free article] [PubMed] [Google Scholar]
  87. Nicholson DA, Freeman JH., Jr Developmental changes in evoked Purkinje cell complex spike responses. Journal of neurophysiology. 2003b;90(4):2349. doi: 10.1152/jn.00481.2003. [DOI] [PubMed] [Google Scholar]
  88. Nicholson DA, Freeman JH., Jr Developmental changes in eyeblink conditioning and simple spike activity in the cerebellar cortex. Developmental psychobiology. 2004;44(1):45. doi: 10.1002/dev.10149. [DOI] [PubMed] [Google Scholar]
  89. Nordholm AF, Thompson JK, Dersarkissian C, Thompson RF. Lidocaine infusion in a critical region of cerebellum completely prevents learning of the conditioned eyeblink response. Behavioral neuroscience. 1993;107(5):882. doi: 10.1037//0735-7044.107.5.882. [DOI] [PubMed] [Google Scholar]
  90. Norris SA, Hathaway EN, Taylor JA, Thach WT. Cerebellar inactivation impairs memory of learned prism gaze-reach calibrations. Journal of Neurophysiology. 2011;105(5):2248–2259. doi: 10.1152/jn.01009.2010. jn.01009.2010 [pii] [DOI] [PMC free article] [PubMed] [Google Scholar]
  91. Ohtsuki G, Piochon C, Adelman JP, Hansel C. SK2 channel modulation contributes to compartment-specific dendritic plasticity in cerebellar Purkinje cells. Neuron. 2012;75(1):108–120. doi: 10.1016/j.neuron.2012.05.025. [DOI] [PMC free article] [PubMed] [Google Scholar]
  92. Ohyama T, Nores WL, Medina JF, Riusech FA, Mauk MD. Learning-induced plasticity in deep cerebellar nucleus. The Journal of neuroscience. 2006;26(49):12656. doi: 10.1523/jneurosci.4023-06.2006. [DOI] [PMC free article] [PubMed] [Google Scholar]
  93. Person AL, Raman IM. Purkinje neuron synchrony elicits time-locked spiking in the cerebellar nuclei. Nature. 2012;481(7382):502–505. doi: 10.1038/nature10732. [DOI] [PMC free article] [PubMed] [Google Scholar]
  94. Rasmussen A, Jirenhed DA, Hesslow G. Simple and complex spike firing patterns in Purkinje cells during classical conditioning. Cerebellum. 2008;7(4):563. doi: 10.1007/s12311-008-0068-2. [DOI] [PubMed] [Google Scholar]
  95. Raymond JL, Lisberger SG, Mauk MD. The cerebellum: a neuronal learning machine? Science. 1996a;272(5265):1126–1131. doi: 10.1126/science.272.5265.1126. [DOI] [PubMed] [Google Scholar]
  96. Raymond JL, Lisberger SG, Mauk MD. The cerebellum: a neuronal learning machine? Science. 1996b;272(5265):1126. doi: 10.1126/science.272.5265.1126. [DOI] [PubMed] [Google Scholar]
  97. Salin PA, Malenka RC, Nicoll RA. Cyclic AMP mediates a presynaptic form of LTP at cerebellar parallel fiber synapses. Neuron. 1996;16(4):797–803. doi: 10.1016/s0896-6273(00)80099-9. [DOI] [PubMed] [Google Scholar]
  98. Sanchez-Campusano R, Gruart A, Fernandez-Mas R, Delgado-Garcia JM. An agonist-antagonist cerebellar nuclear system controlling eyelid kinematics during motor learning. Front Neuroanat. 2012;6:8. doi: 10.3389/fnana.2012.00008. [DOI] [PMC free article] [PubMed] [Google Scholar]
  99. Schneiderman N, Fuentes I, Gormezano I. Acquisition and extinction of the classically conditioned eyelid response in the albino rabbit. Science. 1962;136(3516):650. doi: 10.1126/science.136.3516.650. [DOI] [PubMed] [Google Scholar]
  100. Schonewille M, Belmeguenai A, Koekkoek SK, Houtman SH, Boele HJ, van Beugen BJ, De Zeeuw CI. Purkinje cell-specific knockout of the protein phosphatase PP2B impairs potentiation and cerebellar motor learning. Neuron. 2010;67(4):618–628. doi: 10.1016/j.neuron.2010.07.009. [DOI] [PMC free article] [PubMed] [Google Scholar]
  101. Schreurs BG, Alkon DL. Rabbit cerebellar slice analysis of long-term depression and its role in classical conditioning. Brain Res. 1993;631(2):235–240. doi: 10.1016/0006-8993(93)91540-9. [DOI] [PubMed] [Google Scholar]
  102. Schreurs BG, Gusev PA, Tomsic D, Alkon DL, Shi T. Intracellular correlates of acquisition and long-term memory of classical conditioning in Purkinje cell dendrites in slices of rabbit cerebellar lobule HVI. J Neurosci. 1998;18(14):5498–5507. doi: 10.1523/JNEUROSCI.18-14-05498.1998. [DOI] [PMC free article] [PubMed] [Google Scholar]
  103. Schreurs BG, Oh MM, Alkon DL. Pairing-specific long-term depression of Purkinje cell excitatory postsynaptic potentials results from a classical conditioning procedure in the rabbit cerebellar slice. J Neurophysiol. 1996;75(3):1051–1060. doi: 10.1152/jn.1996.75.3.1051. [DOI] [PubMed] [Google Scholar]
  104. Schreurs BG, Sanchez-Andres JV, Alkon DL. Learning-specific differences in Purkinje-cell dendrites of lobule HVI (Lobulus simplex): intracellular recording in a rabbit cerebellar slice. Brain Res. 1991;548(1–2):18–22. doi: 10.1016/0006-8993(91)91100-f. [DOI] [PubMed] [Google Scholar]
  105. Schreurs BG, Tomsic D, Gusev PA, Alkon DL. Dendritic excitability microzones and occluded long-term depression after classical conditioning of the rabbit’s nictitating membrane response. J Neurophysiol. 1997;77(1):86–92. doi: 10.1152/jn.1997.77.1.86. [DOI] [PubMed] [Google Scholar]
  106. Sears LL, Steinmetz JE. Dorsal accessory inferior olive activity diminishes during acquisition of the rabbit classically conditioned eyelid response. Brain research. 1991;545(1–2):114. doi: 10.1016/0006-8993(91)91276-7. [DOI] [PubMed] [Google Scholar]
  107. Shibuki K, Gomi H, Chen L, Bao S, Kim JJ, Wakatsuki H, Itohara S. Deficient cerebellar long-term depression, impaired eyeblink conditioning, and normal motor coordination in GFAP mutant mice. Neuron. 1996;16(3):587. doi: 10.1016/s0896-6273(00)80078-1. [DOI] [PubMed] [Google Scholar]
  108. Steinmetz AB, Buss EW, Freeman JH. Inactivation of the ventral lateral geniculate and nucleus of the optic tract impairs retention of visual eyeblink conditioning. Behavioral neuroscience. 2013;127(5):690. doi: 10.1037/a0033729. [DOI] [PMC free article] [PubMed] [Google Scholar]
  109. Steinmetz JE, Lavond DG, Thompson RF. Classical conditioning in rabbits using pontine nucleus stimulation as a conditioned stimulus and inferior olive stimulation as an unconditioned stimulus. Synapse. 1989;3(3):225. doi: 10.1002/syn.890030308. [DOI] [PubMed] [Google Scholar]
  110. Steinmetz JE, Logan CG, Rosen DJ, Thompson JK, Lavond DG, Thompson RF. Initial localization of the acoustic conditioned stimulus projection system to the cerebellum essential for classical eyelid conditioning. Proceedings of the National Academy of Sciences of the United States of America. 1987;84(10):3531. doi: 10.1073/pnas.84.10.3531. [DOI] [PMC free article] [PubMed] [Google Scholar]
  111. Steinmetz JE, Rosen DJ, Chapman PF, Lavond DG, Thompson RF. Classical conditioning of the rabbit eyelid response with a mossy-fiber stimulation CS: I. Pontine nuclei and middle cerebellar peduncle stimulation. Behavioral neuroscience. 1986;100(6):878. doi: 10.1037//0735-7044.100.6.878. [DOI] [PubMed] [Google Scholar]
  112. Steinmetz JE, Rosen DJ, Woodruff-Pak DS, Lavond DG, Thompson RF. Rapid transfer of training occurs when direct mossy fiber stimulation is used as a conditioned stimulus for classical eyelid conditioning. Neuroscience research. 1986;3(6):606. doi: 10.1016/0168-0102(86)90057-x. [DOI] [PubMed] [Google Scholar]
  113. Thompson RF. The search for the engram. Am Psychol. 1976;31(3):209–227. doi: 10.1037//0003-066x.31.3.209. [DOI] [PubMed] [Google Scholar]
  114. Thompson RF, Thompson JK, Kim JJ, Krupa DJ, Shinkman PG. The nature of reinforcement in cerebellar learning. Neurobiology of learning and memory. 1998;70(1–2):150. doi: 10.1006/nlme.1998.3845. [DOI] [PubMed] [Google Scholar]
  115. Voneida TJ. The effect of brachium conjunctivum transection on a conditioned limb response in the cat. Behavioural brain research. 2000;109(2):167. doi: 10.1016/s0166-4328(99)00169-2. [DOI] [PubMed] [Google Scholar]
  116. Weeks AC, Connor S, Hinchcliff R, LeBoutillier JC, Thompson RF, Petit TL. Eye-blink conditioning is associated with changes in synaptic ultrastructure in the rabbit interpositus nuclei. Learning and Memory. 2007;14(6):385–389. doi: 10.1101/lm.348307. 14/6/385 [pii] [DOI] [PMC free article] [PubMed] [Google Scholar]
  117. Yeo CH, Hardiman MJ, Glickstein M. Classical conditioning of the nictitating membrane response of the rabbit. I. Lesions of the cerebellar nuclei. Experimental brain research. 1985;60(1):87. doi: 10.1007/BF00237022. [DOI] [PubMed] [Google Scholar]

RESOURCES