07 Jun The ageing slow wave
Memory consolidation is dependent on slow wave spindle coupling during sleep. This study demonstrates that the loss of coupling is a proposed biomarker of cognitive decline, neurodegeneration and neurological disease. There are distinct subtypes of spindles that occur during slow wave sleep (SWS), throughout human development and ageing.
Slow waves occur during stages N2 and N3 of NREM sleep, and within this sleep stage slow waves are associated with global synchronisation of neuronal groups. Spindles are produced and potentiated via cortical-thalamic loops and the coordination of these is generated from the reticular nucleus of the thalamus. Spindles play a role in the regulation of global synaptic function. During normal aging there is a decline in slow waves and spindle activity and is highly associated with cognitive decline.
Spindle subtypes include “early-fast” spinldes, which occur commonly in stage N2 sleep and “late-fast” spindles, which are more commonly seen in stage N3 sleep. Each of these subtypes contain unique coupled-spindle timing and frequency, and these patterns change across the life-span.
It is indicated that the reactivation of memory circuits is activated by the co-ordination of slow wave spindles oscillation during SWS, where higher frequency oscillations or ripples, are imbedded within spindles and contain specific patterns of hippocampal memory reactivation. Slow waves, spindles and ripples combine to maintain a triple coupling relationship that supports synaptic plasticity and remodelling of cortical networks during sleep to promote memory consolidation.
Loss of spindle coupling integrity has been noted in young adults, where the timing of slow wave-spindle coupling is compromised and further deterioration in coupling is linked to brain atrophy and deficits in sleep dependent memory performance in older adults. The loss of slow wave-spindle coupling is identified as a possible biomarker to early pathogenesis of Alzheimer’s Disease. Understanding the pathophysiology of the abnormalities of spindle coupling may provide insights into the important role of sleep in protecting against neurodegenerative disease.
Full articles accessed via: https://doi.org/10.1093/sleep/zsab125
Brice V McConnell, Eugene Kronberg, Peter D Teale, Stefan H Sillau, Grace M Fishback, Rini I Kaplan, Angela J Fought, A Ranjitha Dhanasekaran, Brian D Berman, Alberto R Ramos, Rachel L McClure, Brianne M Bettcher, The aging slow wave: a shifting amalgam of distinct slow wave and spindle coupling subtypes define slow wave sleep across the human lifespan, Sleep, 2021;, zsab125, https://doi.org/10.1093/sleep/zsab125