Self Comes to Mind

recalled. The situation you are in makes a difference for the emotional apparatus. You may be actually inhabiting a scene of your life and responding to a musical performance or to the presence of a friend; or you may be alone and remembering a conversation that upset you the day before. Whether “live,” reconstructed from memory, or created from scratch in one’s imagination, the images initiate a chain of events. Signals from the processed images are made available to several regions of the brain. Some of those regions are involved in language, others in movement, others in manipulations that constitute reasoning. Activity in any of those regions leads to a variety of responses: words with which you can label a certain object; rapid evocations of other images that allow you to conclude something about an object; and so forth. Importantly, signals from the images that represent a certain object also land in regions capable of triggering specific kinds of emotional chain reaction. This is the case of the amygdala, for example, in situations of fear; or of the ventromedial prefrontal cortex in situations causing compassion. The signals are made available to all these sites. However, certain configurations of signals are likely to activate one particular site—provided the signals are sufficiently intense and the context is appropriate—and not activate the other sites where the same signals are also available. It is almost as if certain stimuli have the right key to open a certain lock, although the metaphor does not capture the dynamics and flexibility of the process. This is the case of fear-causing stimuli, which often activate the amygdalae and succeed in triggering the fear cascade. The same set of stimuli is not as likely to activate other sites. On occasion, however, certain stimuli are ambiguous enough to activate more than one site, leading to a composite emotional state. A bittersweet experience is the result, a “mixed” feeling arising from a mixed emotion.
    In many respects, this is the strategy that the immune system uses to respond to invaders from outside the body. White blood cells called lymphocytes carry, on their surfaces, a huge repertoire of antibodies that match an equally large number of possible invader antigens. When one of these antigens enters the bloodstream and is allowed to make contact with lymphocytes, it will eventually bind with the antibody that best fits its shape. The antigen fits the antibody as a key does a lock, and the result is a reaction: the lymphocyte produces that antibody so abundantly that it will help destroy the invading antigen. I have proposed the term emotionally competent stimulus to echo the immune system and highlight the formal similarity of the emotional device to another basic device of life regulation.
    What happens after “the key fits the lock” is nothing short of disturbing, in the proper sense of the term, since it amounts to an upset of the ongoing life state at multiple levels of the organism, from the brain itself to most divisions of the body proper. Again, in the case of fear, the upsets are as follows.
    The nuclei in the amygdalae dispatch commands to the hypothalamus and to the brain stem that result in several parallel actions. The heart rate changes, and so do the blood pressure, the respiration pattern, and the state of contraction of the gut. The blood vessels in the skin contract. Cortisol is secreted into the blood, changing the metabolic profile of the organism in preparation for extra energy consumption. The muscles in the face move and adopt a characteristic mask of fear. Depending on the context in which the fear-causing images appear, one may then freeze in place or run away from the source of danger. Freezing or running, two very specific responses, are exquisitely controlled from separate regions of the brain stem’s periaqueductal gray (PAG), and each response has its particular motor routine and physiological accompaniment. The freezing option automatically induces quiescence, shallow breathing, and a decrease in heart rate, which is an advantage in the attempt to be motionless and elude the attention of an attacker; the running option automatically increases heart rate and enhances blood circulation to the legs because one does need well-nourished leg muscles to run away. Moreover, if the brain selects the running option, the PAG automatically dampens the pain-processing pathways. Why? To better reduce the risk that a