By Douglas Lisle, Ph.D. and Alan Goldhamer, D.C.
When you climb into a hot tub, it pays to edge in slowly. The water can be so hot as to be unpleasant—until you get used to it. Then it will feel pleasant. When you step into a swimming pool, the water sometimes feels cold. But after a few minutes, you get used to it. The scent of a Christmas tree or fragrant flowers is wonderful—at first. But then you get used to it, and soon you may hardly even notice it. How is it that our internal experience can change so dramatically, even when our environment is staying the same? How is it that we so easily “get used to” things? It turns out that scientists have carefully studied this striking phenomenon, which they refer to as neuroadaptation. This process is called “neuroadaptation” because it involves nerves and adaptation.
Our sensory processes are dependent upon the activation of sensory nerves. It is through the activation of various sensory nerves that we are able to see, hear, smell, sense touch, and to taste. The activity of these various sensory nerves tells our brain what is going on, and to what degree of intensity. For example, when you are sitting in a dimly lit room, and you turn on more light, your visual nerves become more active. This causes you to notice an increase in brightness. Similarly, if you increase the volume on your stereo, your auditory nerves become more active. This same principle works for all of the five senses.
We tend to think that our nerves provide us with a very accurate depiction of real-world stimulation. Surprisingly, this is not the case. Let’s go back to the example of sitting in a dimly lit room. If you turn on all of the lights, it will seem very bright. However, if you later go outside into full sunshine, that will seem brighter still. When you go back inside, it will seem dim—even though all of the lights are still on. Clearly, your nerves are not providing you with an “accurate” depiction of reality in these instances. They are providing a relative depiction. Your senses are highly responsive to change. They tell you when a new stimulus is brighter or dimmer, louder or softer, hotter or colder, and so forth, but not precisely how bright, or loud, or hot. Perception is largely a gauge of relative change.
When there is a sudden increase in stimulation, your nerves increase their rate of “firing” (the basic mechanism that communicates sensory information to the brain). Any change in the intensity of a stimulus results in a change in the firing rate of the appropriate sensory nerves. For example, when you brighten the lights, your visual nerves will increase their firing rate. When you later dim the lights, the firing rate will be reduced.
In this article, we shall focus on an aspect of “getting used to” things that can lead to life-threatening mistakes.
After we brighten the lights in a room, our visual nerves increase their firing rate—but only for a short while. After a few minutes, the firing rate will slow down, or “adapt,” to the new, higher rate of stimulation. Sometimes, the nerves may even slow down their response to the level that they were previously firing at the lower level of illumination. This is why even a brightly lit room will seem merely “normal” after your sensory nerves adjust to it.
All of our sensory nerves work in this manner. When we first enter an office, we might be distracted by a noisy air conditioner. But after a while we may cease to notice it. When a person first starts smoking cigarettes, he is acutely aware of the smell of the smoke. He smells it on his fingers, in his clothes, and in his car. But before long, he won’t notice it at all. He will have “gotten used to it.” His sense of smell has adapted to the constant presence of this stimulus. The smoker may not notice much of the smell unless he quits smoking. Only then will his sense of smell re-calibrate to a more smoke-sensitive state. Then he will be able to smell the smoke—just like everyone else does.
Like our other sensory nerves, our taste buds also will “get used to” a given level of stimulation—and this can have dangerous consequences. The taste buds of the vast majority of people in industrialized societies are currently neuroadapted to artificially high-fat, high-sugar, and high-salt animal and processed foods. These foods are ultimately no more enjoyable than more healthful fare, but few people will ever see that this is true. This is because they consistently consume highly stimulating foods, and have “gotten used to” them. If they were to eat a less stimulating, health-promoting diet, they soon would enjoy such fare every bit as much. Unfortunately, very few people will ever realize this critically important fact. Instead, nearly all of these people will die prematurely of strokes, heart attacks, congestive heart failure, diabetes, and cancer as a result of self-destructive dietary choices.