By Claire Su

Original article: Afraid of the dark: Light acutely suppresses activity in the human amygdala

Elise M. McGlashan, Govinda R. Poudel, Sharna D. Jamadar, Andrew J. K. Phillips, Sean W. Cain

There is something about the darkness and the fear that comes along with it. It feels so tangible, yet so uncontrollable. But when it comes down to it, maybe it is all in our heads. Light is known to play an important role in our lives as it provides a way for humans to see, but that is not all that it does. It assists the brain to regulate our circadian clock, mood [1], and ovulation cycle [2]. With seemingly longer days due to artificial lighting, ovulation in humans has seen to be accelerated 2, circadian rhythms have lost their pattern, and moods have been shifted. Light suppresses the amygdala, also known as the emotional control for the brain, and creates a better connection between the amygdala and vmPFC, used for fear extinction. Due to a better connection between those two, it decreases anxiety.

          McGlasha, Poudel, Jamadar, Philipps, and Cain decided to uncover the relationship between light and mood. They wanted to know if the amygdala was the connection between those two points and how exactly light affects people’s moods.With the assistance of twenty-four healthy adults, they had them be exposed to either dim (10 lux) or moderate (100 lux) light intensities while taking an MRI scan. A neurosynth tool was able to detect the connectivity between the amygdala and vmPFC mask. The MRI results showed that the amygdala voxels had greater suppression during 100 lux, which was of moderate light intensity. The connection between the amygdala and vmPFC was extremely strong when there was a light source, and it was quite weak when the participants were exposed to the dark[3].

          While the amygdala voxels were suppressed more during moderate light exposure in comparison to the dim light exposure, there is still evidence that showed that even during low levels of light, the brain still processes non-visual light responses. However, the way that the brain takes in the information differs from person to person. People who have decreased light sensitivity or are less exposed to light are known to be linked to mood disorders [4]. In the experiment done by Brown and Jacobs, the article shared that “participants reporting inadequate natural light in their dwellings were 1.4 times (95% confidence interval [CI] 1.2,1.7) as likely to report depression and 1.5 times (95% CI 1.2, 1.9) as likely to report a fall compared with those satisfied with their dwelling's light” [5]. After some enhancement of natural lighting, the reports of depression decreased 4. This data shows that there is still a difference between how the body perceives natural light and artificial light. However, the human body does not really quite understand that. When we notice that we feel happier during the daytime while the sun is up, we try to replicate that feeling at night 1. The brain tries to seek out light at night and ends up settling for artificial light, but by doing that, it interferes with our circadian rhythm. Gooley shared that “compared with dim light, exposure to room light before bedtime suppressed melatonin, resulting in a later melatonin onset in 99.0% of individuals and shortening melatonin duration by about 90 min” [6].

          It is important to note all the benefits that come from light without ignoring the harms of too much light. There is also a significant difference between artificial light and natural light. As a society, we try to replicate as much as we can from the natural world. But we must come to understand that things that come from nature are going to be the best version possible and should utilize it as much as we can. When we were younger, we all had that seemingly irrational fear of the dark and what could be hidden behind the dark haze. However, the fear of darkness comes naturally due to the amygdala not being suppressed and the lack of connection to vmPFC to eradicate the feeling. So next time you are feeling scared, turn on a dim light source and maybe your brain will figure its own way out of the hole of fear it dug for itself [7].

[1] “Afraid of the dark: Light acutely suppresses activity in the human amygdala” 1.

[2]  “The effects of light on the human body” 1.

[3] Afraid of the dark: Light acutely suppresses activity in the human amygdala” 4.

[4] Afraid of the dark: Light acutely suppresses activity in the human amygdala” 6.

[5] “Residential Light and Risk for Depression and Falls: Results from the LARES Study of Eight European Cities” 1.

[6] “Exposure to Room Light before Bedtime Suppresses Melatonin Onset and Shortens Melatonin Duration in Humans” 1.

[7] Afraid of the dark: Light acutely suppresses activity in the human amygdala” 1.

References

Brown, Mary Jean, and David E. Jacobs. “Residential Light and Risk for Depression and Falls: Results from the LARES Study of Eight European Cities.” Public Health Reports, vol. 126, no. 1_suppl, 2011, pp. 131–140., doi:10.1177/00333549111260s117.

Gooley, Joshua J., et al. “Exposure to Room Light before Bedtime Suppresses Melatonin Onset and Shortens Melatonin Duration in Humans.” Endocrine
Reviews, vol. 32, no. 1, 2011, pp. 155–156., doi:10.1210/edrv.32.1.zef155b.

McGlashan, Elise M., et al. “Afraid of the Dark: Light Acutely Suppresses Activity in the Human Amygdala.” PLOS ONE, vol. 16, no. 6, 2021, doi:10.1371/journal.pone.0252350.

Wurtman, Richard J. “The Effects of Light on the Human Body.” Scientific American, vol. 233, no. 1, 1975, pp. 68–77., doi:10.1038/scientificamerican0775-68.