Afraid of the dark? Blame your brain, not the monsters under the bed

Fear is a common reaction to the dark, especially in children, and now scientists think they may have figured out what causes it – mechanisms triggered in several areas of the brain.

The amygdala is responsible for processing emotions and regulating the fear response, and a new study shows how brain activity in this area changes when exposed to light and darkness.

“Light, compared with darkness, suppressed activity in the amygdala,” the researchers write in their published paper. “Moderate exposure to light resulted in greater suppression of amygdala activity than dim light.”

Moreover, light enhanced the connection between the amygdala and the ventromedial prefrontal cortex, another part of the brain that is associated with controlling feelings of fear.

The new study analyzed fMRI brain scans of 23 people who were exposed to 30-second periods of dim (10 lux) and moderate (100 lux) light as well as darkness (<1 lux). The scans lasted a total of about 30 minutes.

It was shown that moderate illumination caused a “significant decrease” in amygdala activity, and dim illumination caused a smaller decrease. There was also a higher “functional relationship” between the amygdala and ventromedial prefrontal cortex while the light was on.

In other words, light may support the work of fear control centers in our brains. Scientists will need more data to figure out exactly what is going on, but it has previously been found that disrupted connections between these brain areas are associated with anxiety.

The connection between light, darkness and brain activity is well known: changes in light help us know when it’s time to sleep, affect our alertness levels, and can also affect our mood.

It’s possible that being able to control our exposure to light – something we’ve only recently learned to do in the course of our evolutionary history – could be one way to combat this particular phobia. Light therapy is already widely used to treat illnesses such as depression, although scientists don’t fully understand how or why it works.

The key may lie in so-called photosensitive retinal ganglion cells (ipRGCs), which receive light from the eye and transmit it to various parts of the brain. The next step is to learn more about how they interact with the amygdala.

“Further work will be needed to begin to understand the unique contributions of different subsets of ipRGCs and other photoreceptors to visual and non-visual aspects of light responses,” the researchers wrote.

The study was published in the journal PLOS One.

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