Intracellular study of the cat's primary auditory cortex

Abstract

Intracellular recordings were obtained from 139 neurons in unanesthetized muscle-relaxed cat's primary auditory cortex. Patterns of nerve spike activity evoked by tone bursts, noise bursts, and clicks were similar to those observed extracellularly. Transmembrane recordings exhibited both excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs). For cells which had high or moderate rates of spontaneous spike activity, there was always a close relationship between synaptic input reflected in the average evoked membrane potential and the pattern of spike responses shown in the poststimulus time histogram. Active inhibition had an important role in the determination of patterns of spike activity. Acoustically evoked suppression of spike activity was always accompanied by evoked IPSPs. For cells which had low spontaneous spike activity, evoked IPSPs and subthreshold EPSPs were observed which did not apparently change the pattern of spikes from the cell. Thus evoked PSPs were obtained for a larger set of acoustic stimuli than evoked patterns of spikes. Quantitative data concerning patterns of response evoked by tone bursts, noise bursts, and clicks are given. Records were obtained from 28 ‘idle’ cells. These were presumably neuroglia. Resting potentials of these cells were not modified by acoustic stimuli.