Sleep problems linked to age-related cognitive problems

  • A very large Canadian study found that older adults with chronic insomnia performed significantly worse on cognitive tests.
  • A small study links older adults' increasing difficulties with consolidating memories to poorer synchronization of brainwaves during sleep.
  • A fruitful study shows that oxidative stress drives sleep, and that this is regulated by a specific molecule that monitors the degree of oxidative stress.

Chronic insomnia linked to memory problems

Data from 28,485 older Canadians (45+) found that those with chronic insomnia performed significantly worse on cognitive tests than those who had symptoms of insomnia without any noticable impact on their daytime functioning and those with normal sleep quality. The main type of memory affected was declarative memory (memory of concepts, events and facts).

Chronic insomnia is characterized by trouble falling asleep or staying asleep at least three nights a week for over three months with an impact on daytime functioning (mood, attention, and daytime concentration).

https://www.eurekalert.org/pub_releases/2019-05/cu-cia051519.php

Poor brainwave syncing behind older adults failure to consolidate memories

We know that memories are consolidated during sleep, and that for some reason this consolidation becomes more difficult with age. Now a new study shows why.

To consolidate memories (move them into long-term storage), low and speedy brain waves have to sync up at exactly the right moment during sleep. These brain rhythms synchronize perfectly in young adults, but in old age, it seems, slow waves during non-rapid eye movement (NREM) sleep are not so good at making timely contact with the speedy electrical bursts known as “spindles.”

These difficulties are thought to be due to atrophy of the gray matter in the medial frontal cortex.

The study compared the overnight memory of 20 healthy young adults to that of 32 healthy older adults (mostly in their 70s). Before going to sleep, participants learned and were then tested on 120 word sets. They were tested again in the morning. EEG results from their sleeping brains showed that in older people, the spindles consistently peaked early in the memory-consolidation cycle and missed syncing up with the slow waves.

http://www.futurity.org/memories-sleep-older-adults-1633432/

https://www.eurekalert.org/pub_releases/2017-12/uoc--obd121417.php

Oxidative stress governs sleep

A fruitfly study has shown how oxidative stress leads to sleep. Fruitflies (and, it is believed, humans) have sleep-control neurons that act like an on-off switch: if the neurons are electrically active, the fly is asleep; when they are silent, the fly is awake. The switch is triggered, it appears, by an electrical current that flows through two ion channels, and this, it now appears, is regulated by a small molecule called NADPH.

The state of NADPH reflects the degree of oxidative stress. Sleeplessness causes oxidative stress, driving the behavior of NADPH.

I'm wildly speculating here, but is it possible that increased sleep problems often found with age are linked to a growing inability of this molecule to sensitively monitor the degree of oxidative stress, perhaps due to high levels of oxidative stress??

https://www.eurekalert.org/pub_releases/2019-03/uoo-saa032119.php

Reference: 

[4475] Cross, N. E., Carrier J., Postuma R. B., Gosselin N., Kakinami L., Thompson C., et al.
(2019).  Association between insomnia disorder and cognitive function in middle-aged and older adults: a cross-sectional analysis of the Canadian Longitudinal Study on Aging.
Sleep. 42(zsz114), 

[4477] Helfrich, R. F., Mander B. A., Jagust W. J., Knight R. T., & Walker M. P.
(Submitted).  Old Brains Come Uncoupled in Sleep: Slow Wave-Spindle Synchrony, Brain Atrophy, and Forgetting: Neuron.

[4476] Kempf, A., Song S. M., Talbot C. B., & Miesenböck G.
(2019).  A potassium channel β-subunit couples mitochondrial electron transport to sleep.
Nature. 568(7751), 230 - 234.

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