Barbiturate sensitive components of visual ERPs in a reptile.

The selective effects of methohexital anesthesia were used to differentiate components of visual event-related brain potentials (ERPs) in pond turtles (Pseudemys scripta). Tectal and forebrain omitted stimulus potentials (OSPs) were found to be particularly sensitive to the barbiturate; they are reversibly abolished while the large early wave of the forebrain flash visual evoked potential (VEP; 110-120 ms) is reduced by only 27 +/- 11% and that of the tectal VEP (55-65 ms) is increased by 40 +/- 12%. Concurrent with the decline of the OSP is the loss of late slow wave components (ca. greater than 125 ms) of forebrain and tectal VEPs and the appearance of irregularities in the responses of 5 Hz repetitive flashing. The barbiturate effects on the VEP and recovery cycles are remarkably similar to those reported in mammals.