Figure 1.

Trace eyeblink conditioning requires forebrain input to a cerebellar circuit that mediates conditioning. Four forebrain circuits that interact via thalamic nuclei (shown in red text). The limbic, medial temporal circuit is outlined in dark green and is sensitive the effects of aging. The limbic forebrain circuit is outlined in magenta and is affected during schizophrenia. The basal ganglia circuit is outlined in tan and is affected during supranuclear palsy. The sensory circuit is outlined in light green (the somatosensory system is shown in this example). The cerebellar circuit is shown to the far right. The conditioning stimulus (CS) is conveyed to the cerebellum via mossy fibers originating in the pontine nuclei; the unconditioned stimulus (US) is conveyed via climbing fibers from the inferior olive. AT, anterior thalamus; cACC, caudal anterior cortex; Cd, caudate; DG, dentate gyrus; EC, entorhinal cortex; GPi, globus pallidus internal; MD, medial dorsal thalamus; MNs, motor neurons (facial and accessory abducens for blink conditioning); PFC, prefrontal cortex; PL, prelimbic cortex; PR, perirhinal cortex; rACC, rostral anterior cingulate cortex; rDAO, rostral dorsal accessory olive; RE, nucleus reuniens; RNm, magnocellular red nucleus; RS, retrosplenial cortex; SI, primary sensory cortex; SII, secondary sensory cortex; V, trigeminal nucleus; VA, ventral anterior thalamus; VPm, ventral posterior medial cortex; SNpc, Substantia Nigra pars compacta; SNpr, Substantia Nigra pars reticulata.