Alteration by enflurane of Electrophysiologic correlates of search in short-term memory

Effects of controlled subanesthetic concentrations of enflurane on short-term memory functions and associated scalp evoked potentials were studied in eight male volunteers. Short-term memory processes were assessed through a search task. A series of digits (one, three, five, seven, nine, or 11 digits in each series) was presented visually, followed by a test digit, which in half of the trials was part of the series, and in half of the trials was not. The subject responded by pressing one of two switches, signalling "yes" or "no" accordingly. Averaged evoked potentials elicited by the test digit were obtained from seven sites on the scalp. End-tidal enflurane concentrations between 0.12 and 0.25 per cent increased significantly by 30-40 msec the latency of the components of the evoked potentials reflecting sensory processing, but did not affect their amplitude significantly. This increase could not explain the 287-msec increase in reaction time. Amplitude of late components of the averaged potential reflecting information processing was markedly decreased, which the authors interpret as indicating increased trial-to-trial variation in latency of the late component. The authors conclude that enflurane delays and introduces variance into the short-term memory processes and subsequent decision processes that preced overt responses.