, 2010). After passing the internal capsule, the descending corticothalamic axons send off branches into the thalamic reticular nucleus, which contain GABAergic neurons that in turn project strongly to thalamic relay nuclei, see more including VPM and POM (Pinault et al., 1995; Cox et al., 1997; Crabtree et al., 1998). In addition, the cortex also projects to diencephalic GABAergic neurons in the zona incerta (Mitrofanis & Mikuletic, 1999; Barthóet al., 2007) and the anterior pretectal nucleus (Fig. 6D; Wise & Jones, 1977a; Foster et al., 1989). Neurons in the zona incerta and anterior pretectal nucleus also exert a strong GABAergic inhibition of

thalamocortical neurons in higher order thalamic nuclei, including POM (Barthóet al., 2002; Bokor et al., 2005), with functionally different properties to that arising from the thalamic reticular nucleus (Wanaverbecq BMS-734016 et al., 2008). There are thus multiple pathways providing negative feedback control loops for the corticothalamocortical system. Another prominent region of profuse axonal arborization originating from neurons with soma located in the C2 barrel column of S1 is found in the dorsolateral striatum (caudate–putamen; Fig. 7; Wright et al., 1999; Alloway et al., 1999; Hoover et al., 2003; Alloway et al., 2006). Corticostriatal projections are predominantly

from infragranular layers, but supragranular pyramidal neurons also provide input to the striatum (Royce, 1982; Gerfen, 1989; Cowan & Wilson, 1994). Excitatory input from S1 to the dorsal striatum forms an important pathway for cortex to influence the operation of the basal ganglia, which are thought to be important for motor control and action selection. Unlike the corticocortical and corticothalamic connections, no retrograde labelling by FG or AAV6-cre was observed in the striatum, suggesting a one-way flow of information. Neurons in the caudate–putamen interact with FAD the more

medially located neurons in the globus pallidus. The pallidal neurons in turn influence the thalamus, which of course interacts strongly with cortex, thus completing a long subcortical loop back to the neocortex. Further posteriorly, the S1 axons of infragranular pyramidal neurons make dense termination fields in the deep layers of the superior colliculus (Fig. 8A and B), pons (Fig. 8C and D), red nucleus and spinal trigeminal nuclei (Fig. 8E and F). The superior colliculus (also known as the tectum) is thought to play a prominent role in spatial orientation, for example contributing to saccadic eye movements in the visual system. In the whisker sensorimotor system, the superior colliculus might well contribute to orienting whisker movements to palpate objects and surfaces that have attracted the animal’s attention. Corticotectal neurons projecting from S1 to the superior colliculus (Fig. 8A and B; Wise & Jones, 1977b) might therefore signal the presence of interesting sensory information (Cohen et al.