Physiological properties and pattern of projection of cortico-cortical connections from the anterior bank of the ansate sulcus to the motor cortex, area 4 gamma, in the cat.

The physiological properties of neurons in the postsigmoid gyrus lying along the anterior bank of the ansate sulcus and the pattern of projection of these neurons to the motor cortex, area 4 gamma, were investigated in the cat and the following results were obtained. (1) Neurons lying along the anterior bank of the ansate sulcus receive somatotopically organized afferent input from the skin and deep structures on the contralateral side of the body. (2) Short latency antidromic responses were recorded from all regions along the bank of the sulcus following intra-cortical microstimulation (ICMS) of area 4 gamma. (3) The projection of neurons to area 4 gamma was topographically organized. Neurons in the lateral portions projected to more lateral parts of 4 gamma, whereas neurons in the medial region of the postsigmoid gyrus sent axons to the more medial regions of the motor cortex. (4) In 50 cases, receptive fields were recorded from both the antidromically identified postsigmoid gyrus neuron and from neurons around the activation site in area 4 gamma. In 62% of these instances, both cortical sites received afferent input from within the same part of the periphery.