It’s all about timing…

 It’s all about timing…


“Old Brains Come Uncoupled in Sleep: Slow Wave-Spindle Synchrony, Brain Atrophy, and Forgetting” by Randolph F. Helfrich, Bryce A. Mander, William J. Jagust, Robert T. Knight, Matthew P. Walker. Published online December 14 2017 doi:10.1016/j.neuron.2017.11.020


This interesting report from UC Berkeley highlights age-related decreases in coupling between slow oscillations (SO) and sleep spindles during non-REM sleep, correlated with a reduction in the ability of forming new overnight memories. Although these interactions have been previously proposed as contributing factors to hippocampal memory consolidation, limited evidence exists presently for this theory.

To investigate the coupling between SOs and sleep spindles and their potential substrate, the group combined structural MRI, polysomnography and scalp EEG with the assessment of sleep-dependent hippocampal memory consolidation in young (in their 20s) and older adults (in their 70s). Analyses included non-linear directional cross-frequency coupling methods together with phase-dependent correlation measures to map dynamics underlying SO-spindle synchrony relationships.

The EEG showed that in the aging brain spindles peaked early and showed poor synchronization with the slow waves, while structural MRI showed grey matter atrophy in the medial frontal cortex of older adults.

According the authors, the results provide provide “the first demonstration that (1) the precisely coordinated timing between the cortical NREM SO upstate and the sleep spindle predicts successful hippocampus-dependent memory consolidation; (2) temporal disruption of this coordinated NREM oscillation coupling in older relative to young adults predicts impaired hippocampus-dependent overnight memory consolidation; and (3) one pathological mechanism associated with impairment in spatiotemporal coupling of the cortical SOs with sleep spindles in older adults is the severity of mPFC GM atrophy.”

Matthew Walker, one of the authors of this study stated in an interview for the Berkeley news that the group is not only looking at fundamental neurophysiologic mechanisms involved in overnight memory consolidation but also considering potential therapeutic interventions using electrical brain stimulation to the frontal lobe to amplify slow waves and get them into optimal sync with spindles.


By Monica Metea



Figure: Illustration of a spindle wave (top), artifically generated as the difference of a 19Hz and a 20Hz oscillation and the resulting "carrier" wave of 1 Hz (bottom).

Posted on 29 jan 2018


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