Effects of surgical isolation and tetanization on prepyriform cortex in cats.

Abstract

The averaged evoked potential (AEP) of the normal prepyriform cortex closely resembles a damped sine wave. Local or general anesthesia, severance of the olfactory tract, or removal of the bulb will each reduce the AEP to a single negative peak, denoted the "open loop" response. The background unit and eeg activity are concomitantly suppressed, and induced unit activity occurs in response to single afferent volleys only near maximal stimulus intensity. Undercutting the cortex to sever central connections without damaging the olfactory tract does not alter the waveform, although it does alter the variability of the waveform. In each of the "open loop" conditions tetanizing the remaining olfactory tracts restores the AEP to its oscillatory form. The character of the oscillations closely resembles the normal AEP in relation to changing levels of test stimulus intensity and background input. The mechanism of the oscillatory AEP is entirely contained within the cortex and is subject to extracortical modulation and control. The disappearance of the oscillations following tract section or anesthesia is owing to the loss of normal background input, which can be replaced by tetanizing the remaining tract. It is not the result of opening a corticobulbar loop.