Convulsant and anticonvulsant properties of electroconvulsive therapy: towards a focal form of brain stimulation

Abstract

Electroconvulsive therapy is the most rapidly acting and effective antidepressant treatment. For decades it was believed that the generalized seizure provided the necessary and sufficient conditions for efficacy, while the type and quantity of electricity determined the magnitude of cognitive effects. A series of randomized, double-masked trials at the New York State Psychiatric Institute has disproved this view. By systematically varying electrode placement, electrical dosage, and stimulus waveform, this work demonstrated that efficacy and cognitive effects are highly dependent on current paths and the current density within those paths. Specifically, antidepressant effects are contingent on the recruitment of a sufficiently large neuronal population in prefrontal cortex in seizure initiation. The anticonvulsant properties of ECT are reviewed and it is hypothesized that the magnitude of surround inhibition in a PFC network is the critical feature underlying these effects on efficacy. Given this localization, new forms of brain stimulation that elicit focal PFC seizures should have superior benefit/risk ratios. Magnetic seizure therapy has shown promise, but its development may be hindered by technical problems in delivering a sufficiently powerful stimulus. A new alternative, focal electrically administered seizure therapy (FEAST), is described and early work with non-human primates indicate that FEAST achieves a degree of focality in seizure expression that is not possible with traditional ECT.