Causal evidence for the role of REM sleep theta rhythm in contextual memory consolidation
Let sleeping mice remember
The role of REM (rapid eye movement) sleep for memory consolidation has been discussed for a long time. Boyce et al. used optogenetics to inhibit theta oscillations in the mouse hippocampus during REM sleep (see the Perspective by Kocsis). Both object recognition memory and contextual fear memory were impaired. This consolidation mechanism occurred in a critical time window immediately after training. Disrupting the same system for similar durations during non-REM sleep or wakefulness had no effect on memory.
Abstract
Rapid eye movement sleep (REMS) has been linked with spatial and emotional memory consolidation. However, establishing direct causality between neural activity during REMS and memory consolidation has proven difficult because of the transient nature of REMS and significant caveats associated with REMS deprivation techniques. In mice, we optogenetically silenced medial septum γ-aminobutyric acid–releasing (MSGABA) neurons, allowing for temporally precise attenuation of the memory-associated theta rhythm during REMS without disturbing sleeping behavior. REMS-specific optogenetic silencing of MSGABA neurons selectively during a REMS critical window after learning erased subsequent novel object place recognition and impaired fear-conditioned contextual memory. Silencing MSGABA neurons for similar durations outside REMS episodes had no effect on memory. These results demonstrate that MSGABA neuronal activity specifically during REMS is required for normal memory consolidation.
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Supplementary Material
Summary
Materials and Methods
Figs. S1 to S8
Tables S1 to S9
Resources
File (boyce-sm.pdf)
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Information & Authors
Information
Published In
Science
Volume 352 • Issue 6287 • 13 May 2016
Pages: 812 - 816
History
Received: 9 October 2015
Accepted: 24 March 2016
Copyright
Copyright © 2016, American Association for the Advancement of Science.
RE: REM sleep theta rhythm and memory consolidation
To invoke an ongoing activity in the brain, especially during sleep, as serving a purpose to consolidate the past or previous day's information and for a future purpose is very troubling. One's survival is at stake during sleep, especially during REM sleep, as the antigravity muscles are paralysed. The brain and the cardiovascular and respiratory systems have to work harder to sustain one's life in REM sleep. This is not the time for the brain to 'dream' despite the common notion that we dream during REM sleep. This is also not the time for the brain to dwell in the past, nor to think of the future. When external stimuli are hard to come by the contents of a dream are possibly just one of the innumerable internal stimuli that drive the brain activity, the arousal system and the cardiovascular and respiratory system.
The function and purpose of the brain activity in REM sleep, including the theta rhythm, is possibly related to the existing postural, spatio-temporal, cardiovascular and respiratory challenges of REM sleep and to find the urgently needed solutions to sustain life during sleep. It would be a mistake to invoke the current activity of the brain during sleep, including the theta rhythm, as serving a purpose to consolidate information from the past, for a future purpose.