Suppose you’re being chased by a moose. What can you do to protect yourself? You could hide. You could climb a tree. You could carry moose repellent and apply it liberally. Each of these actions is physically very different, but they all can achieve your desired outcome: safety from a rampaging moose.
In science, this sort of variation is called degeneracy. It means that the same outcome can be produced in multiple ways.
As another example, think about all the times in your life that you’ve been sick with a cold. Each one was the result of a different virus affecting different cells in your body, but the outcome was the same: a week of soggy Kleenex. In fact, degeneracy is a part of virtually all biological systems, from disease to DNA to the brain.
Degeneracy is a key concept in my new book, How Emotions are Made: The Secret Life of the Brain. Each time you feel happy, for example, your brain could be creating that experience using different combinations of neurons. Likewise for every instance of sadness, fear, and every other emotion you’ve ever felt. Even when two instances feel the same, they aren’t necessarily constructed in the same way. Variation is the norm.
Note: I am not saying that all neurons are identical in function. That idea is called equipotentiality, and it’s highly doubtful. I’m just saying that a neuron can do more than one thing; therefore, given any psychological function, you have many combinations of neurons that can and do produce that function.
How do we know that the brain operates by degeneracy? Many scientific studies support this conclusion. One of best-known is a study of a pair of identical twins who suffer from a genetic disease, called Urbach-Wiethe disease, that obliterated a key region in their brains, called the amygdala, which is important for emotion. One twin has unusual difficulty experiencing fear and seeing fear in others, a deficit attributed to her damaged amygdala, but the other twin has a completely normal emotional life. This situation is possible because the brain has multiple ways to construct fear — an example of degeneracy.
These observations about emotion and degeneracy are fairly recent discoveries of the past decade. At the same time, a surprising number of scientists still believe that the brain has dedicated neurons for each emotion, and some claim to have discovered those specialized neurons in a variety of animals. I’ll write about that other viewpoint in my next article.