Neuropsychological studies indicate that hippocampal formation in the human medial temporal lobe (MTL) plays a crucial role in the formation and retrieval of memories for recent events. We have found that components of neural activity recorded from the MTL during recognition memory testing discriminate between repeated and nonrepeated words. Such recordings are made possible via intracranial electrodes implanted for the isolation of seizure foci in epileptic patients. Similar activity can be elicited during lexical decision tasks, where it is also sensitive to stimulus repetition. It has been suggested that repetition effects on lexical decision performance measures are a reflection of procedural learning, unlike the type of learning that underlies recognition memory performance, does not involve the MTL. However similar changes in the MTL response during both lexical decision and recognition memory suggests that a common mechanism contributes to repetition effects across tasks. These potentials provide a juncture for studies at both the psychological and synaptic levels of analysis.
