Figure 2.

Neuronal activity in V1 is shaped by behavioural-state and experience-dependent processes, mediated through the integration of nonvisual inputs. (a) Schematic representing the increased gain in neuronal responses to oriented gratings during locomotion (orange trace) versus stationary periods (black trace). Both additive (as illustrated) and multiplicative gain modulations were reported in V1 excitatory neurons [22^•]. Illustration is based on Ref. [10]. (b) Schematic of representations of reward timing in V1. After the learning of a task associating a visual cue (light bulb) and a reward (blue drop), neuronal responses in V1 predict the timing of reward events by sustaining either an increase or decrease in activity after a visual stimulus onset (grey dotted line) or peaking at the expected reward time (blue dotted line). Illustration is based on Refs. [37, 38]. (c) Schematic of V1 responses during the learning of a visually guided task. Example of a go/no-go task with two oriented gratings and only one grating is rewarded (blue drop). A schematic of the responses of a single neuron to the two presented stimuli show that neuronal discriminability between the rewarded (orange) and nonrewarded (grey) stimuli increases with task learning. On the population level (bottom panel), a higher proportion of neurons in V1 show increased selectivity to task-relevant gratings after learning (purple). Illustrations are based on Ref. [43]. (d) Schematic of responses to spatial expectation of visual stimuli in V1. Top panel: schematic of a paradigm where animals are presented with a sequence of visual cues along a virtual track. Traces illustrate neuronal responses to visual cues, before (black) and after (orange) repeated exposure to the same sequence. A population of V1 neurons show specific responses to a given visual stimulus (e.g. vertical grating) but also specific responses for a given stimulus at a particular spatial location (response to vertical grating at B2 location larger than B1). With experience, a population of neurons develop predictive responses, shifting the onset of their response to before the appearance of their preferred stimulus (orange trace). Bottom panel illustrates the effect of omitting an expected stimulus in a trained sequence. On the population level, when the stimulus is present there is an evoked response to the stimulus (black trace), but when the stimulus is un-expectantly omitted (orange trace), there is a large and delayed increase in activity. A subpopulation of neurons respond selectively to these omission events, and not to the initially expected stimulus. Illustration is based on Ref. [28^•]. (e) Schematic of the major cortico-cortical inputs to V1, including top-down influences from higher visual areas (V2), the retrosplenial cortex (RSC) and secondary motor regions (A24b/M2) as well as inputs from other sensory modalities such as the primary auditory cortex (A1) and the somatosensory cortex (SS). Inputs from higher visual areas (V2) include connections from lateral, medial and mediolateral secondary visual areas. (f) Schematic of neuromodulatory and thalamocortical inputs to V1 that have been shown to influence V1 activity in awake behaving mice. LP, Lateral posterior nucleus; dLGN, dorsal lateral geniculate nucleus; MLR, mesencephalic locomotor region.