After-effects of intracellular polarization of single cortical neurons

Abstract

Intracellular and “partially intracellular” recordings from neurons of the sensorimotor cortex of unanesthetized rabbits were used to study after-changes in firing rate arising after stopping a current passing through the recording microelectrode. Against the background of current action, slow, adaptive changes in firing rate were observed. After stopping a depolarizing current, in all intracellularly recorded neurons afterinhibition developed, while stopping a hyperpolarizing current was followed by afteractivation. The duration of after-effects increased with an increase in duration and strength of the current, to reach 10 sec for intracellular recordings. No significant changes in membrane potential level or changes in synaptic bombardment were found which could satisfactorily explain the after-effects. In most cells, during the inhibitory after-effect, large depolarization waves were observed, which did not produce discharges although they exceeded the threshold level (EK) observed before polarization. Sometimes direct measurements show changes in EK to correspond to the after-effect. It is concluded that after-effects described above are not due to interaction between polarized neurons and their neighbors, but to adaptive properties of cortical cell membranes.