Representation of the body by single neurons in the dorsolateral striatum of the awake, unrestrained rat
Authors: Carelli Regina M. , West Mark O. 
Published: January 2005

Single cell recordings in awake monkeys and cats have demonstrated that individual body parts are represented within striatal subregions receiving projections from somatic sensorimotor cortex. Literature indicating that the lateral striatum of the rat receives similar cortical inputs and subserves sensorimotor functions prompted a study of whether this subregion contains similar representations of the body. Single cell recordings were obtained from 923 neurons of 24 awake, unrestrained rats. Of 788 neurons categorized according to body part, 264 (34%) discharged in relation to active movement, passive manipulation, and/or cutaneous stimulation of a particular part of the body; the remainder were related to global, whole body movement (38%) or were unresponsive (28%). Neurons related to individual body parts were recorded throughout the entire anterior‐posterior extent of the dorsolateral striatum (+ 1.60 to –2.12 mm A‐P, from bregma), intermingled among each other in all 3 dimensions. Two topographic arrangements were observed. First, neurons that fired rhythmically, in phase with low frequency (5–6 Hz) whisking of the vibrissae were segregated in the caudal striatum (–0.2 to –2.12 mm A‐P) from neurons related to other body parts, which were distributed from + 1.6 to –0.8 mm A‐P. Second, representations of the head and face were located ventral to those of the limbs, despite substantial overlap in their overall distributions. A prominent feature of individual electrode tracks was the clustering together of cells related to the same body part.

Neurons related to body parts exhibited substantial diversity, which took several distinct forms. Some neurons fired during movement or sensory stimulation in any direction, whereas others showed selectivity for a particular direction. Certain neurons responded to sensory stimulation of a large unilateral region of the body (e.g., all vibrissae or the entire forelimb), whereas others responded to stimulation of highly restricted regions (e.g., a single vibrissa or a single forepaw digit). Finally, neurons differed in the extent to which they exhibited active and passive properties. Among vibrissae‐related neurons, one group fired rhythmically during whisking but did not respond to sensory stimulation of the vibrissae; a second group responded to sensory stimulation of the vibrissae but did not fire rhythmically during whisking; a third group showed both properties. Among limb‐related neurons, firing during active movement was a property of every cell; none showed sensory responsiveness without showing a relation to active movement of one limb. Of the limb‐related neurons, 89% tested responded to passive manipulation of the limb to which the neuron was actively related, and 71% also responded to cutaneous stimulation. Such differences represent a range of striatal mechanisms that presumably reflect various aspects of this structure's participation in movement.

Taken together with studies showing a relative lack of individual body part representations in more medial striatal subregions, these findings support the notion that medial and lateral subdivisions of the rat striatum differ functionally. Regardless of the lack of a compact internal capsule in the rat, numerous important similarities between the lateral striatum of the rat and the putamen of other species suggest that the two regions are homologous. Thus “caudate nucleus” as often used to describe the rat caudate‐putamen, is a misnomer.