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[Responses of visual cortex neurons in the rabbit to direct stimulation by a current of varying intensity]
Abstract
Responses of 47 visual cortical neurons to intracortical electrical stimulation by single biphasic pulses of increasing intensities in the range of 150-2700 microA were investigated. Analysis of response components of each single neuron has demonstrated that their thresholds are similar and those for different neurons vary from 150 to 600 microA. With an increase of the current intensity different neuronal responses type are revealed (concerning the number of impulses in different response phases). They are stable, gradual and selective responses. An increase of the current intensity induces a decrease of the proportion of stable responses (from 26% to 11%) and a slight increase in the proportion of selective responses (from 21% to 32%) in cases of more remote phases of the neuronal response. The fact that selective responses can be detected in all intervals of the analysis indicates, probably, that there are optimal current values for maximal neuronal responses. Elongation of the inhibitory pause takes place in all neurons investigated. The results may be of practical use in researches of human visual prosthesis.
The dependence of neuronal reactions on the location of the stimulating electrode, and the intensity, frequency, and duration of stimulation was investigated in experiments on surviving sections of the neocortex of the guinea pig. The character of the response was maintained in the majority of the neurons only at a slightly suprathreshold intensity of stimulation, a quite low frequency of its presentation (0.1 imp/sec), and a limited duration of the series of stimuli (10-30) with a following 5-10 min break. More intense, high-frequency, or too prolonged stimulation led, as a rule, to a temporary suppression of impulse reactions. Excitation spread more readily in a radial direction, rather than a tangential direction, at identical linear distances to the points of stimulation.
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