God Soul Mind Brain

like a mother taking care of babies.

    Another location produces a paralyzing fear.

    I am a little hesitant to admit it, but in my own lab we have confirmed the presence of the sex nucleus in humans by placing a volunteer (me) in an MRI brain scanner. We showed the volunteer some pictures of scantily clad women, and were able to find a focused spot of activity about 2 millimeters wide in the expected sex nucleus of the hypothalamus. We are in the process of mapping out the emotion nuclei in humans, and so far the nucleus for sexual arousal has the strongest signal and is the easiest to map.

    Each one of these emotion nuclei is a mass of thousands of neurons and is about 2 millimeters wide. The emotion nuclei are packed together in the hypothalamus like peas in a sack. If they were strictly separate from each other, we would probably be emotionally simpler creatures. But as with any adjacent parts of the brain, there is some blurring at the boundaries and probably cross-wiring among the emotional nuclei. I often wonder if this crosstalk is a type of synesthesia or bleeding of one sense into another. Perhaps some of our stranger and darker emotional mixing comes from faulty wiring among these nuclei due to their tight packing. Why else would some people find eating to be sexually arousing? What is the adaptive value of such a strange connection? My speculation is that it has no adaptive value at all, and is a consequence of a wiring error between the nearby hunger and sex nuclei.

    The emotional rabbit hole. A highly simplified diagram of one hemisphere showing the cerebral cortex projecting to the amygdala, which in turn projects to the emotion nuclei of the hypothalamus.

    Diagram 9-1

    Each emotion nucleus sends signals widely around the brain and body. It is presumably this wide-ranging connectivity that creates the emotional state. For example, the hunger nucleus sends output that ultimately affects the gut, the salivary glands, and the cerebral cortex, coordinating the state of hunger. The cerebral cortex in turn sends signals to the hypothalamus, but not directly. It does so to a great extent through a conduit, a little relay, a subcortical brain area about the size of an acorn, called the amygdala (which means “almond” in Latin, a nicely descriptive name).

The amygdala

    There is one amygdala on each side of the brain. This nucleus acts like a switchboard communicating between the vast mantle of the cerebral cortex and the ancient drives of the hypothalamus. The amygdala links thoughts and pictures and words, represented in the cortex, to their emotional content represented in the hypothalamus.

    For example, a smoker knows his cigarettes are killing him; he is trying to quit; but he looks at the pack sitting on the table and in his gut he wants them. His amygdala connects up the sight of the cigarettes, coded in cortex, with the part of his hypothalamus that wants.

    Someone looks at a juicy hamburger and suddenly feels hungry. The image of the hamburger is processed in his visual cortex, as I described in Chapter 6. Ultimately the visual cortex sends that information to the amygdala, which pings the hunger nucleus in the hypothalamus.

    A vegetarian might have the opposite reaction. She might feel repulsed by the hamburger. Due to her training, her upbringing, her recent habits, she has learned a different set of connections through her amygdala, linking the sight of a hamburger to the disgust nucleus in the hypothalamus.

    If someone knows in his heart of hearts that the New Testament is right and good, that feeling is a result of his amygdala connecting the thought in the cortex to an emotion in the hypothalamus. It does not require him to erect an intellectual argument; it is an inner conviction.

    Among the more disturbing properties of the amygdala is the way it links faces with emotions. Scientists such as Phelps and her colleagues, and Wheeler and Fiske, have put volunteers in a brain scanner, shown them pictures of faces, and measured the activity in the amygdala. Mom’s face—channeled from the face neurons in cortex, through the amygdala, to the hypothalamus—leads to a warm and positive feeling. So far so good. But subtle racism is also channeled at least partly through the amygdala. It appears that everyone has learned some degree of unconscious racism toward faces of specific colors and features. This racism is difficult to eliminate because it is not an intellectual belief; it is not a