The effects of electroconvulsive shock on the primary cortical auditory potential

Background: Recording of evoked potentials provides an ideal method of quantifying the acute changes in neurophysiological activity that occur following the administration of electroconvulsive shock (ECS) or electroconvulsive therapy. Methods: Serial recordings of the primary cortical auditory evoked potential (PCAEP) were made from 20 adult male albino rats starting immediately after the induction of generalized seizure activity by ECS. Results: Directly after ECS, the PCAEP was abolished; however an auditory potential that superficially resembled an abnormal PCAEP was invariably present during this period On analysis, it was shown that this response was of probable thalamic origin, which had become unmasked due to the temporary absence of the normally dominant cortical potential, Within 1 min, the genuine PCAEP had begun to reappear and its normal morphology was then rapidly restored. Conclusions: It was concluded that the principal site of action of ECS on the PCAEP may lie quite discretely within the cortex, while auditory activity generated in brain stem and subcortical locations is largely immune to its effects, It is suggested that the loss of the cortical waveform following ECS may be due to epileptogenic events responsible for the development of the paroxysmal depolarization shift, which temporarily block the formation of the postsynaptic PCAEP. The relevance of these findings for an understanding of the therapeutic efficacy of electroconvulsive therapy is discussed. (C) 1998 Society of Biological Psychiatry.