There is lots to love about winter: the beautiful snow, fun activities and holiday cheer. But we all know it’s also accompanied short and dark days, quick tempers, an extra five pounds, and decreased productivity.
What if, this can be neurologically explained? What if the precious eight hours of sunlight that we get during the winter days just isn’t enough?
Our brain and body are more in tune with our surroundings than we give them credit for. The body operates in sleep-wake cycles, called Circadian Rhythms, that correspond with environmental cues such as sunlight. These cycles are managed and created by the hypothalamus which is a region of the brain responsible for essentially, the entirety of our survival. The hypothalamus has a tall task of regulating hunger, thirst, sleep, and attachment behaviors, just to name a few.
Within the hypothalamus is a structure called the Suprachiasmatic Nucleus which (SCN) which is the master clock. The SCN synchronizes all of the other tissues in our bodies to do their thing at the right time by using hormones as the messengers.
The problem occurs when external factors cause a lag time between the SCN signaling and the responses of various tissues throughout your body, called peripheral tissues. This can occur when your circadian cycle is disrupted or when you are experiencing situations such as jet lag. If all goes right in these circumstances eventually, after a few circadian cycles, the SCN and the other parts of your body should resynchronize. However, each peripheral tissue does this at a different rate. In this case, the SCN could constantly be trying to play catch up causing large physiological and psychological disturbances.
These disturbances can be widespread throughout the body affecting a broad range of functioning. As stated before, hormones are a large player in maintaining your body’s stable state and functioning throughout the cycle of a day. Examples of common hormones include melatonin for sleep, cortisol for stress, and TSH for metabolism. Therefore, untimely or imbalanced secretions of these hormones can have harmful effects.
Another reason circadian cycles have overwhelming influence over the whole body is because of CLOCK genes. These CLOCK genes are transcribed into CLOCK proteins that are necessary for the generation and regulation of circadian rhythms. Due to the fact that one gene can code for the production of numerous proteins, they can have a large downstream effect.
Now, the main question is: what happens when all of this gets disrupted? One study conducted in 2010 investigated this using rats as subjects. They put one group of rats in conditions that emulated a normal 24 hour cycle (12h sunlight, 12h darkness). The other group was placed in a shorter 20 hour cycle (10h sunlight, 10h darkness). The results of their over 10 week stay provides some interesting insight into how messing with our internal clocks, messes with our whole body. Let’s break it down.
That Extra Five Pounds.
The mice that were placed in the shorter cycle showed significant weight gain compared to the control group by the end of the study despite the fact that their food consumption was the same as the controls (Karatsoreos, Bhagat, Bloss, Morrison, McEwen 2011) . A possible explanation may be the increased amounts of the hormones leptin and insulin. Insulin acts as a gatekeeper of sugar into your cells. Therefore the more insulin, the more sugar can enter your cells. If this sugar isn’t used, it’s stored as fat. Leptin works to decrease your appetite. So less leptin can cause excessive food consumption and weight gain. In short, a disruptive environment led to an imbalance of hormones causing weight gain (without the enjoyment of more food!)
SUMMARY: Shorter Sleep Cycle = ⬇ Leptin + ⬆ Insulin + ⬆ Weight
The Quick Temper.
Further results of the research show that the mice in the disrupted rhythm condition had damage to the neurons in the prelimbic cortex (Karatsoreos, Bhagat, Bloss, Morrison, McEwen 2011). This region of the brain is involved with emotion regulation. It is also connected to the amygdala which manages threat and fear. Together they work to elicit an emotional response to fearful or stressful situations. The mice in the experimental condition showed less hesitation for confrontation than those in the regular condition. Perhaps this can help explain those annual Christmas dinner fights that everyone loves so much.
SUMMARY: Short Sleep Cycle = ⬇Social Inhibition + ⬆ Emotionality
The Slow Work Progress.
The ability of the mice in the experimental group to complete a spatial learning task was equal to that of the controls however they showed a decreased cognitive flexibility which is the ability to adjust learned memories when presented with further information (Karatsoreos, Bhagat, Bloss, Morrison, McEwen 2011). Additional research has found that humans who work on irregular schedules (they used flight crews as subjects) had decreased performance on hippocampus based memory tasks, such as remembering facts or events. These deficits in retaining and adjusting memories could lead to overall less efficiency in getting work done.
SUMMARY: Shorter Sleep Cycle = ⬇Cognitive Flexibility + ⬇ Hippocampus functioning
What this is all really saying is that 24 is the lucky number. Evolutionarily, our bodies have become accustomed to the standard 12 hours of sunlight, 12 hours of darkness and act accordingly. And like most things, it doesn’t want to change. So bottom line is: From November to February: eat the cookie, make the jab, take a long lunch break.
SUMMARY: It’s all just circadian rhythms anyway.
References
Karatsoreos, I. N., Bhagat, S., Bloss, E. B., Morrison, J. H., & McEwen, B. S. (2011, January 25). Disruption of circadian clocks has ramifications for metabolism, brain, and behavior. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3029753/
Sharpe, J., M., Killcross, & Simon. (2012, December 12). Prelimbic Cortex Contributes to the Down-Regulation of Attention Toward Redundant Cues. Retrieved from https://academic.oup.com/cercor/article/24/4/1066/327218
Shahid, Z. (2018, December 9). Physiology, Hypothalamus. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK535380/
On Psychology and Neuroscience 