Duration of Sodium Amytal Effect: Behavioral and EEG Measures

Summary: In performance of an intracarotid sodium amytal test duration of action is a critical factor since measurements obtained after cessation of action are invalid. Duration of action is often monitored by measuring handstrength contralateral to injection or by visual inspection of amytal-induced EEG slow waves ipsilateral to injection. We describe new objective methods of monitoring drug effect: quantified EEG and sensory discrimination. In a first study of patients with scalp electrodes, the two traditional and the two new measures were compared in 40 injections. Results indicated that the two EEG measures did not differ significantly and estimated a shorter drug effect than the two behavioral measures, which were also not significantly different. The two new measures had a smaller SD, indicating that they may be less erratic. In a second study of 14 patients, using intracerebral electrodes, we showed that slow waves in the frontocentral region lasted as long as the motor and sensory effects, but also that slow waves in the medial temporal region dissipated earlier than the motor and sensory deficits. Our results suggest that motor and sensory measures may overestimate the time in which valid testing can occur if hippocampal function is at issue.