Monday, September 30, 2013

Larks vs. Night-Owls: What Your Sleep Patterns Say About You

Ugh, Monday morning really kicked my butt. Even my strong coffee failed to wake me up completely. Of course, I drag-ass most mornings, being almost useless before 10 a.m. On the flip side, I have always been wonderfully alert and productive after 7 p.m. A night owl I am, and this seems like a good topic for discussion. What determines your circadian rhythms and what does that mean for your personality?

A circadian rhythm is an endogenous, near 24 hour cycle in the process of living organisms (plants, animals, fungi, cyanobacteria). They have clear patterns and are important in determining physiological processes and activities. They are adjusted to the local environmental cues, like the light-dark cycle. I point this one out specifically because we are looking at the sleep-wake rhythm. Now, as with all things, there are individual variations, and a diurnal preference (or “morningness-eveningness (M-E) dimension” or nocturnality) is one of them. Your preference categorizes you into one of two chronotypes: (1) a lark or early riser who goes to sleep early in the evening and wakes up early in the morning or (2) a night owl who goes to sleep late in the evening and wakes up late in the morning.

Did you know that this preference is actually genetically controlled? Yeah. A paper published in Science in 2007 by Godinho et al. used N-ethyl-N-nitrosourea (ENU) mutagenized mice and screened alterations in circadian wheel-running activity. These screenings revealed a group of animals with a longer than average circadian period. They named the mutant gene “after hours” (Afh) and mapped the dominant phenotype. Then they selected those mice displaying the most extreme circadian phenotype for a genome scan. This scan revealed that the Afh mutation results in the substitution of serine for Cys358 (C358S) in Fbxl3, an F-box protein with leucine-rich repeats. Basically, Afh is a variant of the Fbxl3 gene, one of a large gene family that controls the breakdown of specific proteins in the body’s cells. After the identification of this variant, the researchers looked at the circadian expression profiles using in situ hybridization, immunohistochemistry, and Western blotting. They found that Afh affected steady-state levels of the principal negative-feedback regulators of the clock (Period genes Per1 and Per2, Cryptochrome gene Cry1, and the positive regulator Bmal1). One of the key components was the Cry1 gene which delayed the Cry protein breakdown, slowing the molecular feedback loops and lengthening the circadian cycle.

Now that we have our genotype (and resulting sleep-wake phenotype) explanation, let’s move on to personality traits. There is a rather expansive amount of literature showing that larks exhibit optimal cognitive function earlier in the day and night owls later in the day (hmmm…maybe I can coin the term “morning drag-ass syndrome”? MDAS? Pronounce that Midas because it’s gold!) A paper published in 1999 by Roberts and Kyllonen examined these cognitive differences, notabally intelligence, in a study of 420 participants. The participants were United States Air Force recruits undergoing their six week basic training and, as such, had known, homogeneous sleep-wake cycles, dietary intake and social constraints. These recruits completed two self-report measures of circadian type (Morningness-Eveningness Questionnaire and Composite Circadian Scale), a standardized intelligence test (Armed Services Vocational Aptitude Battery or ASVAB), and a standardized memory and processing test (Cognitive Abilities Measurement Battery or CAM-IV). The results of this study showed that night owls scored higher in measures of memory, processing speed, and general intelligence. I almost feel like I need to insert an immature, raspberry-accompanied I’m-smarter-than-you dance in here. Almost.

Admittedly, this final topic was the genesis for this post. I came across a newly published paper about the “Dark Triad” and just had to stop and read it. I mean, Dark Triad? Sounds like something Harry Potter might battle. Basically, the Dark Triad is a psychological term that describes a set of traits that include the tendency to seek admiration and special treatment (narcissism), to be callous and insensitive (psychopathy), and to manipulate others (Machiavellianism). Lovely. Granted, there are other determinations (google The Dirty Dozen Scale….awesome name!), but summing them all up gives you a picture of a person who is basically a giant toolbag. And there is some evidence suggesting there may be a genetic correlation to these traits. This new paper by Jonason, Jones, and Lyons looks at how the Dark Triad may be associated with the night owl chronotype. They had at 263 participants take online assessments that measured the three traits as well as the Morningness-Eveningness Questionnaire. The results of this study showed a correlation between being a night owl and the Dark Triad. The authors do a pretty good job at attempting to explain why this is so, hypothesizing that these Dark Triad traits may be evolutionarily important. They posit that these traits may give some type of night-time specialization, facilitate a cheater strategy, and enable a protean social style. They did not find any sex differences which eliminates sexual selection from their argument. This is sad because they were only able to use male “night-time adventures” once in their explanation. An overall interesting study that both allowed me to say Dark Triad a lot while removing all want to immaturely dance around.

If you have stayed with me this long then I commend you! In my defense, you did get three papers instead of the usual one. But anyway, what are we to take from all of this? That because I’m a night owl I am also an intelligent jerk, and that I can’t help it because it’s all genetic? Oh dear, I hope not. While I like to think I am intelligent, I hope that I am not a narcissistic ass-hat. So, what I guess that I’m saying is take of this what you will, and maybe read more studies.

ResearchBlogging.orgSofia I. H. Godinho, et al. (2007). The After-Hours Mutant Reveals a Role for Fbxl3 in Determining Mammalian Circadian Period Science, 316 (5826), 897-900 DOI: 10.1126/science.1141138

ResearchBlogging.orgRichard D. Roberts, & Patrick C. Kyllonen (1999). Morningness±eveningness and intelligence: early to bed, early to rise will likely make you anything but wise! Personality and Individual Di€fferences, 27, 1123-1133 DOI: 10.1016/S0191-8869(99)00054-9

ResearchBlogging.orgPeter K. Jonason, Amy Jones, & Minna Lyons (2013). Creatures of the night: Chronotypes and the Dark Triad traits Personality and Individual Di€fferences, 55, 538-541 DOI: 10.1016/j.paid.2013.05.001

(image via the Sleepio blog)
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