Auditory evoked potentials from auditory cortex, medial geniculate nucleus, and inferior colliculus during sleep-wake states and spike-wave discharges in the WAG/Rij rat

Objective: Click auditory evoked potentials (AEP) were simultaneously recorded from the auditory cortex (ACx), the medial geniculate nucleus (MGN), and the inferior colliculus (IC) in the freely moving WAG/Rij rat, to investigate state-dependent changes of the AEP in different anatomical locations along the auditory pathway. Methods: AEPs obtained during active (AW) and passive wakefulness (PW), slow wave sleep (SWS), rapid-eye-movement sleep (REM) and generalized spike-wave discharges (SWD; a specific trait of the WAG/Rij rat, a genetic model for absence epilepsy), were compared. Results: The early components in ACx, MGN and IC were stable throughout the sleep-wake cycle and SWD, apart from a slight increase in the IC during SWD. At all three locations a prominent enlargement of a later component (i.e., N32 in IC, N33 in MGN and N44 in ACx) was found during SWS and SWD. Conclusions: The early AEP components are not modulated by the normal sleep-wake states, and are nor impaired during SWD. A strong state-dependent modulation of a later AEP component occurs at all three anatomical locations investigated This suggests that apart from the thalamic burst firing mode, additional mechanisms must exist for the enlargement of the AEP during EEG-synchronized states at the prethalamic and cortical level. (C) 2001 Elsevier Science B.V. All rights reserved.