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C h e c k o u t A B M P P o c k e t P a t h o l o g y a t w w w. a b m p . c o m / a b m p - p o c k e t - p a t h o l o g y - a p p . 81 technique THE SOMATIC EDGE The Hand in the Brain By Til Luchau The hands figure large in the brain. By comparison to the rest of the body, our brain dedicates gigantic areas of its sensory homunculus (Image 1) to hand sensation. Only the super-sensitive tongue and lips come close to the amount of brain area the hands have. In the case of the mouth, the sensorimotor nuances of speaking and oral expression, as well as biting and masticating our food, are so neurologically demanding that they also require comparatively huge areas of the brain. Like the mouth and face, the hands are also extremely sensitive. This and their similarly intricate motor control require comparatively vast regions of the brain to process, map out, and coordinate. And manual therapists will appreciate that since we have two hands but only one mouth, the total amount of brain dedicated to processing hand signals is, in total, far greater than any other part of the body. In the brain, the hands are the largest of the body's regions. Left: the body, sized proportionately to the amount of sensory-processing area in the brain. Right: tractography-based reconstruction of association and projection tracts within the brain's homuncular cortex. The hand and fingers' regions (green, red, and yellow) are not only the largest, but also the most complex in their interconnections within the brain. Modified from originals (left: by Mpj29; from Catani et al., 2012) and used under CC BY-SA 4.0 licenses. leg/toes leg/toes hand/digits hand/digits tongue/ mouth Your hands are truly sense organs. Each hand has about 100,000 nerves, and each of its five fingertips has over 3,000 mechanoreceptive nerve endings, most of which are finely attuned to pressure. Of the 20 different kinds of nerves in the hand, the majority (60 percent) are afferent (sensory nerves, carrying information to the brain), with the remaining 40 percent being efferent (motor nerves, sending movement signals to the muscles of the hand). 1 For hands- on practitioners, these hand facts suggest some interesting thought experiments: • What would your bodywork be like if, like the nerves of the hands itself, it was 60 percent sensing and only 40 percent "output?" Would that change your pacing, the quality, or the feel of what you do? Practitioners who focus on perception (rather than focusing solely on manipulation) know that client satisfaction is often not related to the amount of practitioner output, but rather on the quality of touch, perception, and interaction. • Or, what if, in a whole-body session or series, we followed the homunculus's virtual body proportions when we decide how much time we spend on different parts of the actual body? The back and legs, for instance, would be our focus for only a small fraction of the on-table time, while the hands would take the bulk of the session. This is something like what it would take for the brain to get an evenly distributed whole-body session. WHAT ABOUT PAIN? Though pain involves different nerves than tactile sensation, pain sensitivity is also much higher in the hands (especially the fingertips) than anywhere else on the body. So when the hands hurt, they can "fill" our awareness at the same disproportionate scale 1

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