Memory recall dependent on gene influencing hippocampus-based circadian clock | Hacker News Reader

Memory recall dependent on gene influencing hippocampus-based circadian clock

nature.com

55 pointsbookofjoe13 comments

Perhaps my thinking is flawed and grossly oversimplified here. Doesn't this just seem to line up with brain chemistry and how everything seems to work in the brain? When I drink a coffee, caffeine inhibits adenosine from accumulating in the brain which makes me feel more "awake". Eventually that chemical wears off and I start to get sleepy. I would imagine much like mood memory recall is dependent on some chemical in the brain, of which there is a limited supply. Sleep allows for cleaning and regeneration of said supplies.

What if its not because of the time of day, its just that once you've been awake for a certain number of hours your brain is running on empty until you sleep again? If you had folks working(and acclimated to) the graveyard shift I would expect similar results on memory recall but in the morning hours.

>If you had folks working(and acclimated to) the graveyard shift I would expect similar results on memory recall but in the morning hours.

Only anecdotal, but I had a friend that worked graveyard shift for a few months and when she could get proper sleep during the day it was pretty much like that. She'd be awake and energetic around 10 or 11 pm, worked through her shift, would go through that same early 'morning' productive push and that after 'lunch' slump and by morning she'd be tired and kind of hazy before she went to sleep. It just ended up being she'd never get proper sleep during the day to the point she was tired and hazy all the time and couldn't take it any more and had to quit.

During the beginning though, her memory for things was definitely better at night when she first got up. She'd forget things from conversations we'd have in thr morning or sometimes she wouldn't remember them at all and her memory is usually pretty good, sometimes better than mine, with things or wouldn't really be that coherent about what was going on.

Generally, people working night shifts in "normal" settings have worse health and cognitive outcomes than people on equivalent day shifts. (Swing shifts are evil, and do far more damage than either.)

There seem to be two main factors driving that. One is simply that we arrange the world for being awake in the day: night-shift workers get less sleep due to daytime tasks (e.g. going to the bank), and worse sleep because isolating from light and noise is much harder during the day. The other is a bit more subtle: even with a bright office and blackout curtains, nightshift workers get hammered with conflicting time/light signals every time they commute home or go near a window. It's like a vastly worse version of checking staring into a computer screen right before bed.

There are other impacts, too - I've heard of nightshift workers getting something like SAD, and Vitamin D deficiencies are probably common. But all of that applies to people in wholly-artificial light cycles (e.g. submarines or the Arctic), and yet those people seem to cope far better than 'regular' nightshift workers.

As far as "memory recall is dependent on some chemical in the brain", I think you're right. On that front, the study is interesting as "we found a chemical mechanism that's wearing out late in the day". There are obviously a host of chemicals involved in memory recall, and a variety of possible time links (e.g. "we forget over time", "we remember things better in the same context we learned them"), so it's interesting to find chemical channels that respond specifically to time of day and not those other factors.

As far as "What if its not because of the time of day, just hours awake?", the study doesn't seem to have directly distinguished the two possibilities, which is a bit surprising. The study did show that tasks learned at "night" and tested in the morning performed better than the reverse, so it's not all-around tiredness, but it doesn't seem to distinguish whether rhythm or tiredness affected memory. (The day/night cycle was 12-hour, and the tasks were conducted at 4 and 10 hours into light, so the mice weren't "up late", but it was an analogue of 8-9PM.)

I suspect the study avoided differentiating these factors because we're not entirely sure where the differences lie. Broadly, we know at least three components to "tiredness" exist. Adenosine levels rise while awake and fall when sleeping: it's the "awake too long" part of tiredness. Melatonin is produced and broken down rapidly, but looking at (blue) light inhibits its production: that's the "dark out" part of tiredness. But "circadian rhythm" includes more factors we don't totally understand: abruptly adjusting both light and time awake still requires acclimation, and blindfolded people with control over their sleep schedule still respond to light cycles.

So for the mice, all of that was piled together to say "late in a normal day, for whatever reason, these chemical factors impede memory recall". Trying to break out the key elements would be fascinating. I'd love to know what happens with different light cycles, or with the abrupt adjustments like waking the mice up early/late on the day of the test, or after giving the mice caffeine or melatonin. And for the graveyard shift, I suspect it's just a mess all around: people in submarines or Antarctica can have wholly-shifted schedules like these mice, but most night-shift workers operate on shifted sleep schedules and an awful mix of imperfectly-adjusted day/night cycles.

(Hmm... Now I also wonder what happens to the test if you keep mice awake during 'dark', then let them sleep during 'light'?)

Mentions Zeitgeber which I had to look up: https://en.wikipedia.org/wiki/Zeitgeber

I have read of Dementia having “sun downing” issues as patients get worse symptoms around dusk, and care homes having good results by brighter daytime lights and working on day/night rhythms.

Prof. Satchin Panda’s work is on intermittent fasting and circadian rhythms, and in his TED talk he has dementia on a slide as one of the possible problems involved with this kind of metabolic dysregulation.

Now this memory recall depending on circadian rhythm;

So heavy technology (blue light) use literally gives us worse memory. As our economy moves to be more and more attention-based, that sounds about right.

(OT): But...as told years ago... um Some people are better in memorizing things. Someone told me that 'managers can memorize 6 or 7 things correctly' -so i answered: 'Monday, Tuesday, Wednesday, Thursday...-call me a manager!' (-;

And (Disclaimer) sure, this has nothing to do with nothing... or others, but attentional -blink-(crossed out) came to you for an entertaining OT-purpose. ^^

Where do you get that from the article? They even say tha the memory deficits were observed in constant darkness conditions as well (and therefore due to intrinsic clock not extrinsic light per se). Also keep in mind that mice are nocturnal so poor memory performance late in the light period for them is probably analogous to poor memory performance during early morning for us, when there is no light.

I notice that my recall is much better if I had learned the information while moving... either driving a car (actively aware of my surroundings) or on a walk. I can typically think back to exactly where I was when I learned something.

I think I have a related thing going on in my brain. My recall ability is poor to middling, but if I listen to a podcast a second time within a week or two of the first, I have these intrusive and extremely vivid scenes play out in my mind from the first time I listened to the podcast.

I want to try an experiment where I film my first listen, then a week later re-listen and narrate the 'film' without watching it to see how close i am.

Kind of similar experience. As a kid, when we'd go on a road trip, on the way back I'd remember everything I was thinking about on the trip there, but in reverse order. It was the landmarks and scenes that triggered the recall of what I had been thinking about when I saw it the on the trip there.

It's interesting that you cite driving, because I often see people assume this is exercise-linked.

Also interesting: the study doesn't address motion, but it did try to control for the circumstances of learning and recall: if the mice were tested "late in the day", they performed similarly badly whether they had learned the task early or late in the day.

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