Chapter

Interrelationships between epilepsy, sleep, and memory

Nikolai Axmacher

in Epilepsy and Memory

Published in print June 2012 | ISBN: 9780199580286
Published online September 2012 | e-ISBN: 9780191739408 | DOI: http://dx.doi.org/10.1093/acprof:oso/9780199580286.003.0021
Interrelationships between epilepsy, sleep, and memory

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This chapter first summarizes data on the neural correlate of the initial step of declarative memory formation, i.e., of encoding which either leads to a feeling of familiarity or to conscious recollection. It summarizes evidence showing that the relationship between the blood oxygenation level-dependent (BOLD) signal (recorded with fMRI) and the underlying neural activity appears to be particularly ambiguous in the medial temporal lobe (MTL); in particular, the BOLD signal does not convey clear information about the level of excitation or inhibition in this brain region. The chapter focuses on electrophysiological recordings in animals and intracranial EEG data from epilepsy patients. It argues that memory formation relies on an inhibitory signal in the medial temporal lobe, which renders hippocampal and neocortical stimulus representations sparser, and on oscillatory activity in the gamma and theta frequency ranges. The second part of the chapter discusses the relationship of these phenomena to epileptiform activity and to memory impairments in epilepsy patients. It gives a brief overview on the neural patterns underlying the second step of memory formation, consolidation. It then describes overlapping neural phenomena during consolidation and epilepsy, such as sharp waves and ripples/fast ripples.

Keywords: declarative memory formation; encoding; blood oxygenation level-dependent signal; medial temporal lobe; epileptiform activity; memory impairment; consolidation

Chapter.  5883 words.  Illustrated.

Subjects: Neuroscience

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