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J Neurosci. 2018 Aug 22;38(34):7428-7439. doi: 10.1523/JNEUROSCI.2928-17.2018. Epub 2018 Jul 16.

Temporal Expectation Modulates the Cortical Dynamics of Short-Term Memory.

Author information

1
Max Planck Research Group Auditory Cognition, Max Planck Institute for Human Cognitive and Brain Sciences, 04103 Leipzig, Germany, anna.wilsch@gmail.com jonas.obleser@uni-luebeck.de.
2
Experimental Psychology Laboratory, Center for Excellence Hearing4all, European Medical School, University of Oldenburg, 26111 Oldenburg, Germany.
3
Max Planck Research Group Auditory Cognition, Max Planck Institute for Human Cognitive and Brain Sciences, 04103 Leipzig, Germany.
4
Department of Psychology, Brain and Mind Institute, University of Western Ontario, London, Ontario, N6A 3K7 Canada, and.
5
Department of Psychology, University of Lübeck, 23562 Lübeck, Germany.

Abstract

Increased memory load is often signified by enhanced neural oscillatory power in the alpha range (8-13 Hz), which is taken to reflect inhibition of task-irrelevant brain regions. The corresponding neural correlates of memory decay, however, are not yet well understood. In the current study, we investigated auditory short-term memory decay in humans using a delayed matching-to-sample task with pure-tone sequences. First, in a behavioral experiment, we modeled memory performance over six different delay-phase durations. Second, in a MEG experiment, we assessed alpha-power modulations over three different delay-phase durations. In both experiments, the temporal expectation for the to-be-remembered sound was manipulated so that it was either temporally expected or not. In both studies, memory performance declined over time, but this decline was weaker when the onset time of the to-be-remembered sound was expected. Similarly, patterns of alpha power in and alpha-tuned connectivity between sensory cortices changed parametrically with delay duration (i.e., decrease in occipitoparietal regions, increase in temporal regions). Temporal expectation not only counteracted alpha-power decline in heteromodal brain areas (i.e., supramarginal gyrus), but also had a beneficial effect on memory decay, counteracting memory performance decline. Correspondingly, temporal expectation also boosted alpha connectivity within attention networks known to play an active role during memory maintenance. The present data show how patterns of alpha power orchestrate short-term memory decay and encourage a more nuanced perspective on alpha power across brain space and time beyond its inhibitory role.SIGNIFICANCE STATEMENT Our sensory memories of the physical world fade quickly. We show here that this decay of short-term memory can be counteracted by so-called temporal expectation; that is, knowledge of when to expect a sensory event that an individual must remember. We also show that neural oscillations in the "alpha" (8-13 Hz) range index both the degree of memory decay (for brief sound patterns) and the respective memory benefit from temporal expectation. Spatially distributed cortical patterns of alpha power show opposing effects in auditory versus visual sensory cortices. Moreover, alpha-tuned connectivity changes within supramodal attention networks reflect the allocation of neural resources as short-term memory representations fade.

KEYWORDS:

alpha; attention; magnetoencephalography; neural oscillations; sensory memory; temporal expectations

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