________________
Neuroscience & Karma
3. Touching and Pain A. The Skin
The skin contains several different sense-organs, which between them serve the various senses that we call touch, pressure, temperature, and pain. Some of these sensory cells are large and conduct signals rapidly. Others are smaller and slower and still others are free nerveendings, very thin nerve-fibres not attached to any definite receptorstructure in the skin. Each different sort of nerve-ending provides signals for a different sensation. During ordinary life, sense-organs are part of the system of exploratory programs which an animal or man continually employs to satisfy its nceds. The senses of touch, and of pressure, mostly come into action when we do things with our bands and feet. Each of these types of receptor is activated by a somewbat different sort of pressure or deformation of the skin. The various types of sense-organ in the skin do not work independently, and the sensations we feel there, such as degrees of smoothness or roughness, pressure, tingling, tickling, or movement are the result of collaboration at both the spinal and cortical levels between the various signals. B. Cortical Areas for Touch
There are three well-known tracts leading from the skin to the brain. A large area of the cerebral cortex receives the signals from these pathways, all laid out in a regular map, corresponding to the topography of the body surface, but with greater areas for the more functionally important parts. These 'somatotopic' maps are a fundamental feature of the cerebral computer, as they are also for vision. A difference between touch and pain, is that there are active programs for gaining information by touch. We learn to recognize the feel and shape of things, whereas pain is basically inflicted upon us and is formless. Correspondingly, pain bas no cortical representation. The symbolic significance of signals of touch are determined by much more complicated systems of reference, after they have passed through thalamus to the cerebral cortex. C. Programs for Avoiding Damage
Every animal must have programs to ensure withdrawal from
