Dissociable motor roles of the rat's striatum conform to a somatotopic model.

The findings of this study indicate distinctive roles of different regions of the rostral striatum of rat in segmental motor control. In order to test the hypothesis of somatotopically organized motoric functions in the striatum, the effects of bilateral ibotenate-induced lesions of either the dorsomedial or the dorsolateral or the ventrolateral regions of the rostral striatum on reaching movements of the tongue and the forelimbs were examined. Lesions of the dorsolateral region chronically impaired reaching movements of the forelimbs but not of the tongue. Lesions of the ventrolateral region impaired initiation and execution of reaching movements of both the tongue and the forelimbs, with the impairment of forelimb reaching being somewhat less severe than that produced by dorsolateral lesions. Neuronal loss in the medial striatum had no chronic effects on either movements. The impairments of reaching performance reflected failures of motor synergisms between tongue and head and between limb and paw, as well as alterations in the scaling of movement amplitude. These findings support the hypothesis of a motor somatotopy in the lateral region of the rat's rostral striatum and of a critical role of the lateral striatum in initiation, scaling, and coordination of reaching movements.