An analysis of variability in somatosensory cortical neuron discharge

Publisher Website
Google Scholar
Abstract
The spike trains of individual somatosensory cerebral cortical neurons were recorded with extracellular microelectrodes in the absence of general anesthesia. Young adult monkeys (Macaca mulatta) served as experimental subjects. Estimates of neuronal variability were computed from the impulse activity contained within periods (time segments) of stationary activity evoked by constant-velocity tactile stimuli. The variability (as estimated by the SD of the interspike-interval distribution) computed for weakly stationary time segments of stimulus-evoked discharge activity was independent of stimulus parameters. For each of the 165 cortical neurons which were studied, the SD of discharge activity decreased as the mean rate of firing increased, and the relationship between SD and the mean interspike interval (MI) was of the form SD = m .cntdot. MI + b (where m = slope and b = y intercept). In both area 3-1 of S-I and in S-II/r the neuron population which represents the hairy skin of the proximal fore- or hindlimb was heterogeneous; i.e., in each area these neurons can be subdivided into 3 subpopulations, on the basis of the y intercept of the linear relationship between SD and MI for stimulus-evoked discharge activity. Neurons with different y intercept and slope parameters exhibited different discharge patterns as reflected by the shape of the hazard function. The differences in the SD-MI relationship, exhibited by the different subpopulations of somatosensory cortical neurons, may enable the somatosensory cortex to reflect subtle differences in tactile stimulation over a larger range of stimulus intensities than would be possible if all neurons exhibited similar SD-MI relationships.