Siesta time

I'm a morning person.

I know this is pretty unusual.  I also know from first-hand experience that night owls tend to hate us morning people, who are up with the sun and at least reasonably coherent by six a.m., if not always showered and fully dressed.  (Hell, I'm retired.  Fully dressed sometimes doesn't happen at all, especially when the weather is warm.)

The result, though, is that I fade out pretty early in the evening.  I'm one of those people who, when invited to a party, seriously consider saying no if the start time is after seven in the evening.  By eight I want to be reading a book, and the times I'm still awake at ten are few and far between.

But the lowest time for me, energy-wise, is right after lunch.  Even when I get adequate sleep, I go through a serious slump in the early afternoon, even if I was chipper beforehand.  (Okay, given my personality, I'm never really chipper.  I also don't do "perky" or "bubbly."  So think about it as "chipper as compared to my baseline demeanor.")

Turns out, I'm not alone in finding the early afternoon a tough time to be productive, or even to stay awake.  As I learned from a paper in The Journal of Neuroscience, the problem is a fluctuation in the brain's reward circuit -- it, like many other human behaviors, is on a circadian rhythm that affects its function in a regular and predictable fashion.

The problem is a misalignment of the putamen (part of the brain's reward circuit) and the suprachiasmatic nucleus, which acts as a biological clock.  The putamen is most active when you receive a reward you weren't expecting, and least active when you expect a reward and don't get one.  The cycling of the suprachiasmatic nucleus stimulates the putamen to expect a reward after lunch, and then when it doesn't come -- one in the afternoon is nowhere near quitting time or happy hour, and most people's schedules don't accommodate an early afternoon nap -- the expected payoff doesn't happen.

The result: sad putamen.  Drop in motivation levels.

"The data suggest that the brain’s reward centres might be primed to expect rewards in the early afternoon, and be ‘surprised’ when they appear at the start and end of the day," said neuroscientist Jamie Byrne of Swinburne University.  "[The] brain is ‘expecting’ rewards at some times of day more than others, because it is adaptively primed by the body clock."

Me, I wonder why this priming happens at all.  What sort of reward did we receive in the early afternoon in our evolutionary history that led to this response becoming so common?  Honestly, I wonder if it was napping; an afternoon nap has been found not only to improve cognitive function, but (contrary to popular opinion) doesn't generally interfere with sleeping at night.  Having evolved on the African savanna, where the early afternoon can be miserably hot, it could be that we're built to snooze in the shade after lunch, and now that most of us are on an eight-to-five work schedule, we can't get away with it any more.  But the circadian rhythm we evolved is still there, and our energy levels plummet after lunch.

[Image licensed under the Creative Commons Jamain, Sleeping man J1, CC BY-SA 3.0]

It reminds me of the three weeks I spent in Spain and Portugal a few years ago.  I was astonished at first by the fact that no one ate dinner -- even considered eating dinner -- until nine in the evening.  (On one of our first days there, we went to a restaurant at about eight, and asked the waiter if we could be seated at a table.  His response was, "Why?"  I think he was genuinely puzzled as to why anyone might want dinner at such a ridiculously early hour.)  But once we got the hang of it -- a big lunch with a bottle of fine red wine, then a three-hour siesta during the hottest part of the day, when businesses close their doors so there's nothing much to do but sleep anyhow -- even I was able to stay up late with no problem.

All in all, a very pleasant lifestyle, I thought.

So we now know there is a neurological reason for the early-afternoon energy slump.  Kind of a fascinating thing how much we're at the mercy of our biological clock.  But anyhow, I better get busy and get some chores done.  Time's a-wasting, and I'm guessing by lunchtime I won't be feeling like doing much but hitting the hammock and conking out for a while.

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This week's Skeptophilia book recommendation of the week is pure fun, and a great gift for any of your friends who are cryptid fanciers: Graham Roumieu's hilarious Me Write Book: It Bigfoot Memoir.

In this short but hysterically funny book, we find out from the Big Guy's own mouth how hard it is to have the reputation for being huge, hairy, and bad-smelling.  Okay, even he admits he doesn't smell great, but it's not his fault, as showers aren't common out in the wilderness.  And think about the effect this has on his self-image, not to mention his success rate of advertising in the "Personals" section of the newspaper.

So read this first-person account of the struggles of this hirsute Everyman, and maybe even next time you're out hiking, bring along a little something for our australopithecene distant cousin.

He's very fond of peach schnapps.

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]

Naps, rewards, and circadian rhythms

Even when I have gotten enough sleep, which isn't honestly that often, I have a distinct pattern in my energy level.  I tend to be an early riser, and after a barely-coherent half-hour or so in which I make coffee and answer anyone who talks to me in snarly monosyllabic grunts, I have a period of three hours or so during which I'm usually quite productive.  After lunch, there's about two to three hours of slump, when my chief concern is finding a nice quiet corner to curl up and take a nap.  (This doesn't help my 9th period class much, but they're big kids.  They can deal.)

[image courtesy of the Wikimedia Commons]

Late afternoon is usually pretty high energy, but after dinner I fade steadily.  By nine o'clock I'm ready to be reading a book in preparation for powering down for the night.  The times I'm up after ten are rare indeed.

Real party animal, that's me.

I've always been a little curious as to why this is, as it seems to have little to do with external circumstances.  One of those odd circadian rhythms, but what purpose it could serve, I have no idea.

But now a recent piece of research has found a fascinating correlation to this pattern, one that involves the "neural reward center" of the brain, located in the putamen (interestingly, this same part of the brain is involved in several disparate functions, such as motor coordination, category learning, and our perceptions of hatred and disgust).

The current study, entitled "Time of Day Differences in Neural Reward Functioning in Healthy Young Men," was co-authored by Jamie E. M. Byrne, Matthew E. Hughes, Susan L. Rossell, Sheri L. Johnson, and Greg Murray, of Swinburne University (Australia), and appeared this week in The Journal of Neuroscience.  The researchers looked at the degree of activation in the left putamen -- the aforementioned neural reward center -- in sixteen healthy male test subjects, and found out that the peak not only in activity, but the subjects' self-reported feelings of well-being, peaked in the early afternoon.

The authors write:

Reward function appears to be modulated by the circadian system, but little is known about the neural basis of this interaction.  Previous research suggests that the neural reward response may be different in the afternoon; however the direction of this effect is contentious.  Reward response may follow the diurnal rhythm in self-reported positive affect, peaking in the early afternoon.  An alternative is that daily reward response represents a type of prediction error, with neural reward activation relatively high at times of day when rewards are unexpected (i.e., early and late in the day).  The present study measured neural reward activation in the context of a validated reward task at 10.00h, 14.00h, and 19.00h in healthy human males...  Consistent with the ‘prediction error’ hypothesis, activation was significantly higher at 10.00h and 19.00h compared to 14.00h.  It is provisionally concluded that the putamen may be particularly important in endogenous priming of reward motivation at different times of day, with the pattern of activation consistent with circadian-modulated reward expectancies in neural pathways; viz., greater activation to reward stimuli at unexpected times of day. 

Put more simply, our reward centers react more strongly in the early morning and late afternoon because they're kind of surprised when things at those times don't suck.

Which makes me wonder about my own peculiar circadian rhythm.  I know that early-morning types like myself are in the minority, and my perkiness (at least once I've had coffee) at seven AM inspires near-homicidal rage in the typical morning-hater.  Also, I tend to be getting glassy-eyed at the point in the evening when most people are just getting the festivities rolling.

So would I show the opposite pattern in my left putamen than the test subjects in the Byrne et al. study?  Because I definitely wouldn't say my feelings of "positive affect" peak in the early afternoon.  The only thing that peaks around that time is my need for a nice long nap in the hammock.

Or, maybe, I am more productive during the morning and late afternoon because that's when I get the best payback from my reward centers.  In the early afternoon, perhaps my brain says, "Okay, if I'm not gonna get any props for working hard, why bother?  If I'm not appreciated, then screw it, I'm putting my feet up."

I'd love to volunteer for an fMRI and see what's going on in there -- whether my response is explainable from the pattern that Byrne et al. noticed, or if I'm just an aberration.

Be that as it may, the study is pretty cool from the standpoint of demonstrating a neurological underpinning to our behavioral circadian rhythms.  Any lens we can get on the workings of our brains is all to the good.  But I'm gonna wind this up, because my early-morning window of opportunity is wearing on, and I'm pretty sure I'm going to accomplish bugger-all after that.