14 September 2012

Sleep and Memory

Welcome back. You’ll guess from the title that I’m about to go on about how sleep affects memory or, maybe, how memory affects sleep. Considered separately, these are not new topics for this blog. In one of my earliest posts, I discussed sleep--mainly, that I don’t get much. Last March, I reviewed a study that linked forgetting to walking through doorways. You’ve probably forgotten.

Why am I on these topics again? Because I saw the review of a study that stated sleep improved the memory of young adults but did not improve the memory of older folks like me. After leaning back and uttering, “Hmmm,” I decided to look closer.


Pillows. (www.rachelphilipson.com)
Slow-Wave Sleep and Word Retention

The study was from the Emory University School of Medicine, in Atlanta. The researcher enlisted young and old adults, gave them pairs of words and, after 12 hours, tested how well they remembered the second word given the first. The subjects of interest here were tested after a good night’s sleep. Well, as good as it could be wearing a head device that monitored brain waves.

Although young and old got about the same length of total sleep, the monitors indicated that the older adults got only about half as much slow-wave sleep. (Permit me to abbreviate slow-wave sleep as SWS.) SWS is, in essence, deep sleep, and it’s reportedly important for retaining memories (aka, memory storage or consolidation).

When the researcher compared word retention to the amount of SWS, he found a positive correlation for the young adults--the more SWS, the more words they remembered. Not so for the older adults, who scored about the same on word retention regardless of the amount of SWS.

Although I wondered, “But couldn’t it be…” and...”Did you consider…,” it would be presumptuous of me to say much about the results having only seen a review and the pre-publication abstract of the research. So, of course, I will.

Other Studies

Before deciding whether it’s good or bad that we need less SWS as we age to retain memories, I focused on the little I knew about the study. I didn’t know the actual correlations, but correlation measures how closely one factor changes with another, not cause and effect. This study isolated SWS, presumably with good reason, yet I found a slightly earlier study that had different results with total sleep.

Instead of testing with word pairs, researchers from the University of Toronto assessed memories of stories and personal events, comparing retention following sleep and wakefulness. Young and old adults both did better after sleeping than after wakefulness. And…ready?... total sleep correlated highly with memory retention in older adults.

So what’s going on here? Is this really SWS versus total sleep, or is it one of those US versus Canadian things? Wait! There’s a recent study from Italy that found: regular consumption of cocoa flavanols--a chocolate drink--might be effective in improving cognitive function in elderly subjects with mild cognitive impairment.

Forget that the Italian study was funded by the MARS candy company. Did the other studies monitor the hot chocolate their older adults drank before bedding down? Gee, I wonder what the college students drank.

Wrap Up

More work is needed. Yes, that’s one of the primary conclusions of most investigations, but that’s how research proceeds, step by step, some big, some not so big. I just hope they get this straight before they strap a brain-wave monitor on my head. Hot chocolate would be ok. Thanks for stopping by

P.S.

Review and abstract of Emory University memory study:
http://www.myhealthnewsdaily.com/2916-sleep-memory-storage-older-adults.html
http://www.ncbi.nlm.nih.gov/pubmed/22708533
Abstract of University of Toronto memory study:
http://www.ncbi.nlm.nih.gov/pubmed/20182945
Review and abstract of memory study from Italy:
http://www.myhealthnewsdaily.com/2950-chocolate-cognitive-function.html
http://hyper.ahajournals.org/content/60/3/794.abstract?sid=e67ec66a-279a-4a44-8245-23aad005765f

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