Free It's a Jungle in There: How Competition and Cooperation in the Brain Shape the Mind by David A. Rosenbaum

“Yes,” the man replied. 26
    The explanation that Ramachandran gave for this strange effect was based on his knowledge that the face and hand regions of the somatosensorycortex are adjacent. Relying on the idea that neurons try to form connections, Ramachandran suspected that sensory inputs from the young man’s face formed stronger-than-normal connections with the young man’s somatosensory cortex. Ramachandran reasoned that if the hand sector no longer received afferent inputs from the hand, but if touch to the face activated the hand region, then higher centers would treat the inputs as hand-based. Touching the amputee’s face would therefore cause the amputee to think his actually absent hand had been touched.
    Ramachandran’s second observation was even droller. It concerned a topic that might better be talked about behind closed doors. If you’re prudish, skip the next three paragraphs.
    Some people get their jollies by having their feet fondled. Fondling the soles of the feet or sucking and kissing the toes turn on these foot fetishists. Why such stimulation can lead to so much pleasure is a bit of a mystery, except if you follow the line of reasoning that Ramachandran pursued.
    Imagine you’re a neuron—in this case, an afferent neuron projecting from sensory receptors in the foot to the foot region of the somatosensory cortex. Being such a neuron, each time your owner’s foot is touched, you send a signal to the foot zone of the somatosensory cortex. You have no idea, of course, being a neuron, that the signal you’re sending concerns foot touches
per se
. Nor do you know that the region to which you’re sending the signal is the region that gets more signals from the foot than from anywhere else. You’re also unaware that the area next to the foot region happens to be the region that gets signals from the genitals.
    Being a typical neuron, however, you try to form connections with neighboring zones. Happily, from your point of view, some of your foot axons get hooked up with the nearby area, the genital area. Because the genital area sends signals to parts of the brain that elicit pleasure, the outcome is the one of interest: Pleasure comes from foot feels because inputs from the foot also feed the part of the brain that gets inputs from the genitals. If you’re someone in whom this cross-talk is especially strong, you may be especially fond of having your feet fondled.
Synesthesia and Summing Up
    A third strange phenomenon related to neural plasticity is not one that Ramachandran happened to have studied extensively. This one is
synesthesia
. People who experience synesthesia have vivid associations between sights and sounds (to name just two sensory modalities). When they
see
something, they also
hear
something, though what they see is objectively silent. What they hear is also consistently associated with what they see. 27
    Synesthesia is due in part to neural plasticity. Sensory inputs get crossed and go where they normally wouldn’t. A sight leads to an illusory sound because inputs that normally go to visual centers also penetrate auditory centers. Likewise for other cross-modal connections. Synesthesia arises, then, because the nervous system isn’t a perfectly regimented place. Rather, it’s a place where interactions can take on surprising twists and turns. This isn’t to say that what goes on in the nervous system is utterly wild and unpredictable. Neural connectivity has considerable orderliness, as indicated in the opening sections of this chapter, but it’s also subject to considerable variability, as indicated in the final sections, starting with the section on neural plasticity. These and the other functional properties of the brain reviewed here are consistent with the view that it’s a jungle in there. Even in a jungle—neural or otherwise—there’s considerable order, but there can also be staggering variety.

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Pay Attention!
    Earlier in this book you saw how important it