Although the medial temporal lobe is thought to be critical for recognition memory (RM), the specific role of the hippocampus in RM remains uncertain. We investigated the effects of transient unilateral hippocampal electrical stimulation (ES), subthreshold for afterdischarge, on delayed item RM in epilepsy patients implanted with bilateral hippocampal depth electrodes. RM was assessed using a novel computer-controlled test paradigm in which ES to left or right hippocampus was either absent (baseline) or synchronized with item presentation. Subsequent yes-no RM performance revealed a double dissociation between material-specific RM and the lateralization of ES. Left hippocampal ES produced word RM deficits, whereas right hippocampal ES produced face RM deficits. Our findings provide the first demonstration in humans that selective unilateral stimulation-induced hippocampal disruption is sufficient to produce impairments on delayed RM tasks and provide support for the material-specific laterality of hippocampal function with respect to RM.

Lamotrigine exhibits no clinically significant cognitive effects in adjunctive therapy for children with epilepsy.

The clinical use of depth-electrode recording in the hippocampus in people undergoing neurosurgical treatment for epilepsy has also facilitated exploration of hippocampal memory function though stimulation techniques. This chapter reviews the few studies that have used these techniques, combining them with synchronous memory testing. Early studies used techniques involving after-discharges, with the disadvantage of imprecise investigation of focal functionality. More progress was made when subthreshold stimulation techniques were adopted and this led to specific theories about left and right hippocampal involvement. The chapter also introduces an arguably more refined technique termed single-pulse electrical stimulation (SPES), which uses single 1-ms pulses to produce approximately 100–300 ms cortical responses. The SPES technique has produced results indicating a specific role for the hippocampus in episodic memory — encoding rather than retrieval — here termed the gateway theory of hippocampal function.

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