Effects of stimulus parameters on seizure duration and ECS-induced retrograde amnesia

A selected electroconvulsive therapy stimulus dose can result from different combinations of pulse amplitude, pulse width, pulse frequency, and stimulus duration; however, the roles of these stimulus variables in the effects of the overall stimulus dose are not clearly understood. A series of studies on Wistar rats was therefore conducted to assess the effects of different stimulus compositions at constant stimulus charge. In the first two studies, two differently composed 60 mC charge unidirectional electroconvulsive shock (ECS) stimuli were administered once daily for 3 days, while in the third study three differently composed 120 mC charge unidirectional ECS stimuli were administered on a single occasion. At constant charge, a markedly longer stimulus duration was associated with ear burns and an approximately 12.5% longer seizure duration. At constant charge, however, different stimulus compositions were not associated with different degrees of impairment in two passive avoidance models of ECS-induced retrograde amnesia. These preliminary findings have implications for the choice of stimulus settings during dose titration and dose selection procedures. While the findings encourage further investigation, it appears that variations in stimulus duration are biologically significant, but minor variations in other stimulus elements may not influence the effects of electrically induced seizures very much.