RESPONSE PROPERTIES OF NEURONS OF CAT'S SOMATIC SENSORY CORTEX TO PERIPHERAL STIMULI

Abstract

A description is given of a method of recording from single neurons of the first somatic sensory area of the cat''s cerebral cortex; by it the circulatory and respiratory movements of the brain are eliminated. A quantitative criterion of considerable aid in identifying a population of action potentials as those discharged by the same single unit is evolved from measurements of spike amplitudes. Initially negative and initially positive single-unit discharges, both recorded extracellularly, are examined from the standpoint of reliability and degree of cell injury. It is concluded that the former are recorded from cells the less likely to be damaged by the recording electrode, and are more suitable for studies of the functional organization of the cortex. The typical discharge patterns of a neuron of the first somatic cortical area in response to a brief stimulus to its peripheral receptive field is a short train of impulses at high frequency. This repetitive train is a normal event. Its latency, frequency, and number of impulses per response are sensitively dependent upon the properties of the peripheral stimulus. Some complex response patterns, rearely seen under anesthesia, are described. The distribution in depth of the neurons studied corresponds to layers II through VI of the somatic cortex. It is concluded from various lines of evidence that in the normal waking animal cells of all these layers are mediately open to activation by sensory stimuli. The spatial distribution of the potential field developed about an active cortical cell was measured. Its extent, when compared with the degree of interlocking of the dendritic fields of cortical cells, makes ephaptic interaction between those cells possible. A study of the surface-positive, deep-negative primary evoked potential of the cortex was made, as well as of its relation to the evoked discharges of single cortical cells. It is suggested that this wave is the integrated sign of the local postsynaptic responses of large numbers of cortical neurons. The properties of a local spontaneous slow wave event of limited spatial extent within the cortex are described.