Origins of multisynaptic projections from the basal ganglia to the forelimb region of the ventral premotor cortex in macaque monkeys

Abstract

The ventral premotor cortex (PMv), occupying the ventral aspect of area 6 in the frontal lobe, has been implicated in action planning and execution based on visual signals. Although the PMv has been characterized by cortico-cortical connections with specific subregions of the parietal and prefrontal cortical areas, a topographical input/output organization between the PMv and the basal ganglia (BG) still remains elusive. In the present study, retrograde transneuronal labelling with the rabies virus was employed to identify the origins of multisynaptic projections from the BG to the PMv. The virus was injected into the forelimb region of the PMv, identified in the ventral aspect of the genu of the arcuate sulcus, in macaque monkeys. The survival time after the virus injection was set to allow either the second- or third-order neuron labelling across two or three synapses. The second-order neurons were observed in the ventral portion (primary motor territory) and the caudodorsal portion (higher-order motor territory) of the internal segment of the globus pallidus. Subsequently, the third-order neurons were distributed in the putamen caudal to the anterior commissure, including both the primary and the higher-order motor territories, and in the ventral striatum (limbic territory). In addition, they were found in the dorsolateral portion (motor territory) and ventromedial portion (limbic territory) of the subthalamic nucleus, and in the external segment of the globus pallidus including both the limbic and motor territories. These findings indicate that the PMv receives diverse signals from the primary motor, higher-order motor and limbic territories of the BG.