Neuronal activity evoked in cat precruciate cerebral cortex by cutaneous stimulation

Abstract

Extracellular recordings were made of the evoked activity of neurons in the precruciate forepaw cortex of the domestic cat after cutaneous stimulation of each limb. Neurons were classified according to the size of their excitatory receptive fields and whether or not their axons traversed the medullary pyramids. Neurons having bilateral receptive fields confined to the forelimbs and thoracic trunk region comprised 25% of the sample of 690 neurons; by contrast, only 6% of 1020 neurons from postcruciate arm cortex (gathered in a previous study) showed such fields. These neurons discharged with a short latency after stimulation of precruciate arm cortex of the opposite hemisphere; most other wide-field neurons but few small-field neurons responded to such interhemispheric activation. Many of the wide-field neurons responded to light or sound stimulation, or both, whereas few of the small-field neurons, including those with bilateral fields confined to the forelimb region, responded to such stimulation. Many wide-field neurons responded both to light touch and to hair-bending. Most pyramidal tract neurons had wide receptive fields. We concluded that the corticofugal elements in precruciate tissue receive information from cutaneous receptors of various types, distributed widely over the body surface, and that many of these elements are influenced by several modalities of sensory input. The “interneurons” of precruciate cortex, on the other hand, have sharply restricted input channels, and provide the most immediate and powerful modulation of corticofugal elements.