The origins of thalamic inputs to grasp zones in frontal cortex of macaque monkeys
The hand representation in primary motor cortex (M1) is instrumental to manual dexterity in primates. In Old World monkeys, rostral and caudal aspects of the hand representation are located in the precentral gyrus and the anterior bank of the central sulcus, respectively. We previously reported the organization of the cortico-cortical connections of the grasp zone in rostral M1. Here we describe the organization of thalamocortical connections that were labeled from the same tracer injections. Thalamocortical connections of a grasp zone in ventral premotor cortex (PMv) and the M1 orofacial representation are included for direct comparison. The M1 grasp zone was primarily connected with ventral lateral divisions of motor thalamus. The largest proportion of inputs originated in the posterior division (VLp) followed by the medial and the anterior divisions. Thalamic inputs to the M1 grasp zone originated in more lateral aspects of VLp as compared to the origins of thalamic inputs to the M1 orofacial representation. Inputs to M1 from thalamic divisions connected with cerebellum constituted three fold the density of inputs from divisions connected with basal ganglia, whereas the ratio of inputs was more balanced for the grasp zone in PMv. Privileged access of the cerebellothalamic pathway to the grasp zone in rostral M1 is consistent with the connection patterns previously reported for the precentral gyrus. Thus, cerebellar nuclei are likely more involved than basal ganglia nuclei with the contributions of rostral M1 to manual dexterity.
KeywordsIntracortical electrical stimulation Motor cortex Ventral premotor cortex Thalamocortical Cerebellum Basal ganglia
The work was supported by grants from the National Institutes of Health (EY2686 to J.H.K, NS055843 to I.S.). O.A.G was supported by a postdoctoral fellowship from the Canadian Institutes of Health Research followed by a career development award from the National Institutes of Health (K99 NS079471). We are grateful to Drs. Nicole Young, Mary Baldwin, Pooja Balaram, and Barbara O’Brien, for assistance with motor mapping. Laura Trice provided excellent support for histology and Mary Feurtado was instrumental to pre- and post-operative animal care.
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