Think about baking cookies. Your recipe probably includes basic ingredients such as flour, water, sugar, and salt. Now suppose somebody told you that these ingredients are exclusively for making cookies and have no other purpose. From now on, everyone must call them “cookie flour,” “cookie water,” “cookie salt,” and “cookie sugar.” That would be ridiculous. These same ingredients form the core of bread, cakes, sauces, and even non-foods like glue.
The same situation comes up in the science of emotion and in neuroscience more generally. The brain contains general-purpose ingredients, known as core systems, that interact with one another to construct diverse and tasty end-products such as emotions and thoughts. A single core system can play a role in thinking, remembering, decision-making, seeing, hearing, and experiencing and perceiving diverse emotions, and yet is not dedicated to any of these purposes, just as flour and water are not dedicated to cookie-making.
In the past, however, scientists thought these core systems were single-purpose, like essences in the brain, and even named them that way. An example is a brain network called the default mode network, which plays a role in countless mental phenomena: remembering the past, imagining the future, empathy, morality, emotion, and more. This brain network has been rediscovered and named so many times it’s hard to keep track. Scientists who study mental inference refer to this network as the “mentalizing” network or the “theory of mind” network. Others who study how the brain remembers the past call it the “memory” network. Those who study how the brain imagines the future call it the “prospection” network. It has also been called the “empathy” network, the “morality” network, the “context” network, and the “self” network. The nodes of this network also overlap extensively with the brain’s “language” network and are robustly engaged during spontaneous thinking and imagination, and when people work for rewards like food or money, and when they decide between things of value. Whew!
Many neuroscientists now understand the default mode network as a core system that’s involved in all of these phenomena. Core systems are “one to many,” meaning that a group of neurons may play many roles. (This is the converse of degeneracy, which is “many to one”: many different patterns of brain activity can produce the same function.)
Core systems are a vital concept in my book How Emotions are Made: The Secret Life of the Brain. A given instance of happiness, surprise, or any other emotion is constructed by core systems working collaboratively. Remember this next time you read a news article about “the brain circuit” for fear or any emotion being discovered in a rat or a fruit fly. There is no such circuit, any more than there is just one single purpose for flour. Your brain indeed has basic circuits for (say) freezing in place, which is something that animals may or may not do in situations that we’d consider fearful. But freezing does not equal fear. I’ll go into details about that last point in an upcoming post.