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    Emotions: Why and How

    One of my questioners on Quora, asked: “How does the passing around of electrical and chemical signals between neurons in our brains result in feelings and experiences?” In other words, why do humans respond to experiences with some kind of emotion? Why doesn’t the experience just register as a neutral event? A computer works just fine with emotion-free information. However, humans must do something that computers are not obliged to do: that is, act in the world. Acting in the world is enhanced if the triggering information has psychological valence, that is a range of “good-ness” and “bad-ness.” Valence creates passion. Passion generates energetic action.

    We are attracted to things that seem good and avoid things that seem bad, all proportional to the degree of the valence. In evolutionary terms, valence has enormous adaptive value. Evolving animals benefit from being able to assign value to the information in their environment. They make extra effort to pursue what is valuable to their wellbeing and avoid things that are not.

    The animal species existing today, at least the higher species, clearly show signs of assigning value to their experiences, even if we have no evidence that they are consciously aware of their feelings. Dogs, for example, clearly demonstrate such emotions as joy, sadness, disappointment, anxiety, eagerness, and so on.

    Mammalian species are able to assign value because they have a special system in the brain known as the limbic system. This system is not present in fish or amphibians and is only rudimentary in reptiles. The limbic system has highly interconnected clusters of neurons that mediate the various dimensions of emotions. For example, the limbic system’s amygdala is largely involved in generating anxiety and fear, the hippocampus is involved in forming memories and their associated valence, and the hypothalamus regulates viscera and hormone systems to respond according to emotional valence.

    The limbic system is evolutionarily conserved in humans. What is different is that humans have a much more robust cerebral cortex for analysis of emotional valence and behavioral response to it. This is possible because the limbic system is richly connected to cortex via a limbic structure known as the entorhinal cortex. Connections of the limbic system’s dopamine-dependent nucleus accumbens and striatum reach control systems for movements, and thus behavior is informed by emotional valence.

    Emotional valence need not be realized consciously in order to affect behavior. Emotional behavior occurs in primitive mammals, in which we have little reason to believe they are capable of robust consciousness. Even in humans, many emotions go unrecognized, yet still influence behavior. Indeed, a common purpose of psychotherapy aims to help patients recognize their emotions and thus understand them.

    The as yet unanswered question is how the limbic system assigns degrees of good-ness and bad-ness. Clearly, some of the answer comes from feedback from visceral and hormonal systems, which normally are servo-regulated. In a servo-system, good-ness is inherently defined as an experience that supports homeostasis, with bad-ness defined oppositely. Much of the limbic mechanisms involves memory recall, wherein memory of an experience that was originally interpreted by the cortex as beneficial or good, is used to label a similar new experience. Likewise, memory of a bad experience serves to label similar new experiences.

    This still leaves open the question of how neurons can code for good-ness and bad-ness. No doubt, neurons that register good-ness become more active when they receive information that is good. How does the brain known where to send good information and where to send bad information? Likely, this involves intrinsic wiring connections, for example, the fiber tracts that mediate positive reinforcement in the medial forebrain bundle that course through the hypothalamus to connect several limbic structures. No doubt such connections had natural selection advantage during the evolution of the limbic system, just as it was important to evolve other pathways that could mediate negative and perhaps harmful information.

    Even lowly single-cell animals have inherent capability for attraction to beneficial stimuli and avoidance of harmful stimuli. The evolution of a limbic system just allows for a much more robust assignment of valence.

    You can learn more about this in the introductory inexpensive e-textbook, Core Ideas in Neuroscience. For future reference, I will post this answer on my blog site at Psychology Today.

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