Some Factors Governing Sensory Convergence in the Cat’s Motor Cortex

Abstract

The cat’s motor cortex contains neurones whose axons descend in the pyramidal and extrapyramidal corticofugal paths. We have been studying the sensory activation of the pyramidal system as an example of an integrative pathway. Our method has been that of recording extracellular responses from cells in the anterior sigmoid gyrus and in the postcruciate strip, rostral to the postcruciate dimple. The rest of the posterior sigmoid gyrus constitutes the primary somatic receiving area (SI). Neurones in both areas respond to stimulation of skin and joints (Mountcastle 1961; Brooks 1963), but the motor cortex also receives proprioceptive (Oscarsson and Rosen 1963), as well as auditory and visual inputs (Buser and Imbert 1961; Patton, Towe and Kennedy 1962; Brooks 1963; Jung, Kornhuber and Da Fonseca 1963). Another difference between motor and sensory cortex involves the spatial origins of adequate peripheral somesthetic and kinesthetic stimuli. The sensory cortex overwhelmingly receives somatotopic representation of the contralateral body, i. e., impulses from receptors in circumscribed, continuous parts of the body are relayed to a definite part of the contralateral sensory cortex. The sizes of receptive fields of neurones in sensory cortex reflect density of peripheral sensory endings. Fields in densely innervated skin, such as the paws, are smaller than those from proximal, relatively sparsely innervated parts of a limb (Mountcastle 1961).