HOW DOES DARKNESS MANIPULATE THE BRAIN?
In the absence of light, the brain works overtime to understand our surroundings. When the sense of sight fails us, highly complex mechanisms take over to replace it. But instead of simply trusting in the brain’s amazing ability to compensate, we often react with apprehension—with the fear of the dark. We just can’t help it…
1 HOW DO THE OTHER SENSES REACT WHEN WE CAN’T SEE?
When the visual cortex has no images to process, the brain relies on our other senses. After five days in complete darkness, our sense of smell improves, noises seem louder, and we become able to learn Braille much more quickly. But when exposed to 24 hours of normal light afterwards, the visual cortex is reactivated and begins responding to visual stimuli again.
2 HOW QUICKLY DO OUR EYES BECOME ACCUSTOMED TO THE DARK?
When we enter a dimly lit room from outdoors, we can hardly see anything at first. It takes between 20 and 30 minutes for our eyes to adjust completely to the room’s lighting. The key is rhodopsin: Found in the rod cells of the retina, this visual pigment enables vision when the light is dim. Rod cells are very sensitive and bear most of the responsibility for night vision, whereas the cone cells, which are responsible for our color vision, function best in bright light.
3 HOW DOES THE BRAIN PREPARE US FOR SLEEP?
In the dark, the tiny pineal gland found deep within the brain gets to work producing the hormone melatonin, which regulates our sleep patterns. It helps the body prepare for rest: The heart starts to beat more slowly, breathing becomes calmer and more regular, and both blood pressure and body temperature drop.
4 WHERE DOES THE FEAR OF THE DARK ORIGINATE?
Our senses are always at work, and all of the sensory perceptions converge in the center of the brain in the thalamus, which is involved in image processing. When the brain is deprived of visual input, we react with fear. The hypothalamus sends out a message to the adrenal glands to produce a burst of adrenaline. That makes the heart race, putting more oxygen into the bloodstream, and the other senses become more acute.