Peculiarities of inhibition in cat auditory cortex neurons evoked by tonal stimuli of various durations.

The extra- and intracellular responses of 262 neurons in A1 to tones of best frequency with durations ranging from 10 ms to 1.2 min were studied acute experiments on ketamine-anesthetized cats. Following the generation of action potentials in response to the tone stimulus, inhibition of both the background and the auditory stimulus-evoked spike activity were observed in 91% of the investigated neurons. The duration of this inhibition corresponded to the stimulus duration. For the remaining neurons (9%) an inhibition of the stimulus-evoked spike activity alone was seen, also corresponding to the stimulus duration. Maximal inhibition of the spike activity occurred for the first 100-200 ms of the inhibitory response (the period which equalled the time of development of an IPSP in a cell). During this period of IPSP development, the membrane resistance of the neuron was reduced to 60-90% of its initial value. Varying the duration of the acoustic signal within a range of 10-200 ms was accompanied by a change in the IPSP duration and inhibition of the spike activity of the neuron. Whenever the tone lasted more than 200 ms, the membrane potential of the neuron was restored to the resting potential. However, during this period, the responsiveness of the neuron was lower than that initially observed. Measurement of the membrane resistance during the inhibitory pause that was not accompanied by hyperpolarization produced an index with an average 17% lower than the initial value for 87% of the neurons.(ABSTRACT TRUNCATED AT 250 WORDS)