Effects of ethosuximide upon psychomotor responses and electromyographic parameters of healthy individuals

The purpose of this paper was to investigate the effects of anticonvulsant ethosuximide upon physiological parameters, psychomotor reactions and electromyographic criteria. Ethosuximide increased the reaction times to flashes and the choice reaction time in most subjects, often provoked a greater amount of errors during choice reactions and decreased the average heart frequency. The functional activation during the tasks was diminished. The EEG showed no marked qualitative or quantitative changes. Ethosuximide reduced the maximum conduction velocity of the motor nerve and changed the action potential duration but not the action potential shape. There is no exact parallelism between the increase in reaction time and decrease of nerve conduction velocity. The drug effect upon psychomotor reactions seems to be caused by reduction of vigilance and an inhibitory effect upon the individual's motor responsiveness. Like other anticonvulsants, ethosuximide may alter the electrical properties of all excitable membranes and, by this ubiquitous site of action, exerts the described effects.