CORTICAL AND THALAMIC VISUAL-EVOKED POTENTIALS DURING SLEEP-WAKE STATES AND SPIKE-WAVE DISCHARGES IN THE RAT

Flash visual evoked potentials (VEP) were simultaneously recorded from the primary visual cortex and the dorsal lateral geniculate nucleus i n freely-moving WAG/Rij rats, to investigate whether the thalamic VEP shows the same state-dependent alterations as the cortical VEP. VEPs o btained during active and passive wakefulness (AW and PW), slow-wave s leep (SWS). REM sleep and during the occurrence of spike-wave discharg es (SWD), a specific trait of the genetically epileptic WAG/Rij rat, w ere compared. The general architecture of the thalamic VEP resembles t he cortical VEP, although its polarity is reversed. This facilitated t he interpretation of components in terms of underlying neuronal events . The primary excitation peak is differently modulated in cortex and t halamus. Whereas the thalamic component (P30) is not affected by brain -state, the cortical component (N1) shows a strong increase in latency during SWS and SWD. In contrast, the modulation of later components i s highly similar for cortex and thalamus. VEPs obtained during AW and REM resemble each other. During SWS and SWD there is a considerable, a nd during PW a moderate, enlargement of primarily inhibitory component s. After-discharges are enhanced during SWS, SWD and REM. No evidence is found for a major impairment of sensory transmission during SWD. (C ) 1998 Elsevier Science Ireland Ltd.