Behavior-dependent and drug-induced changes of rat visual evoked potential: relation to the EEG spectral power.

The relation between EEG spectral power and alterations of the visual evoked potential (VEP) during different behavioral states and after intraperitoneal application of neuroactive drugs have been investigated in Long-Evans rats. FFT power and field potential maps were made in five behavioral states of the unrestrained rat: exploratory sniffing, face washing, relaxed waking immobility, slow wave sleep, and during cortical high-voltage spindling. Fourteen epidural electrodes were implanted in the bulbus olfactorius, in the frontal areas Fr2 and Fr1, in the visual areas 18 and 17, and in the cerebellum of the right hemisphere. Two regions in the investigated cortex were found to be the probable origins of slow delta and theta waves: the frontal cortex and the anterior area 18. Area 17 does not express prominent EEG frequencies that contribute to the cortical EEG in any of the investigated behavioral states. The VEP was found to originate in area 17. The neural activity of the occipital cortex is reflected in the VEP whereas the occipital EEG possibly reflects the hippocampal activity in some behavioral states. This may be a reason for partly independent changes of VEP and EEG during different behavioral states and after application of neuroactive drugs.