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Comparative Study
. 2008:2008:563028.
doi: 10.1155/2008/563028.

Enhancement of neocortical-medial temporal EEG correlations during non-REM sleep

Nikolai Axmacher  1 , Christoph Helmstaedter, Christian E Elger, Juergen Fell
Affiliations
Comparative Study

Enhancement of neocortical-medial temporal EEG correlations during non-REM sleep

Nikolai Axmacher et al. Neural Plast. 2008.

Abstract

Interregional interactions of oscillatory activity are crucial for the integrated processing of multiple brain regions. However, while the EEG in virtually all brain structures passes through substantial modifications during sleep, it is still an open question whether interactions between neocortical and medial temporal EEG oscillations also depend on the state of alertness. Several previous studies in animals and humans suggest that hippocampal-neocortical interactions crucially depend on the state of alertness (i.e., waking state or sleep). Here, we analyzed scalp and intracranial EEG recordings during sleep and waking state in epilepsy patients undergoing presurgical evaluation. We found that the amplitudes of oscillations within the medial temporal lobe and the neocortex were more closely correlated during sleep, in particular during non-REM sleep, than during waking state. Possibly, the encoding of novel sensory inputs, which mainly occurs during waking state, requires that medial temporal dynamics are rather independent from neocortical dynamics, while the consolidation of memories during sleep may demand closer interactions between MTL and neocortex.

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Figures

Figure 1
Figure 1
Time course of γ 2 and δ band activity in scalp EEG and in the anterior hippocampus and sleep stages during one night in one exemplary subject. S1: sleep stage 1, S2: sleep stage 2, SWS: slow wave sleep.
Figure 2
Figure 2
Pearson's correlation coefficient (Fisher z-transformed) between power densities in scalp EEG (C3/C4) versus medial temporal locations; averages across subjects are depicted. Both in the δ and in higher (α and γ 2) frequency range, correlation values were maximal during NREM sleep.
Figure 3
Figure 3
Power values (mean and standard deviation across epochs) in scalp EEG and medial temporal locations. Please note that to improve visibility of effect of sleep stage, ordinate scaling differs for low- (δ to β 1) and high- (β 2 to γ 3) frequency bands. In contrast to the effect of sleep on power correlations (see Figure 2), power values in the high-frequency band were maximal during waking state.
See this image and copyright information in PMC

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