The Case Against Reality: Why Evolution Hid the Truth from Our Eyes

by Donald D. Hoffman

Activity in a region of the brain called the postcentral gyrus correlates with conscious experiences of touch. The neurosurgeon Wilder Penfield reported in 1937 that stimulating this gyrus with an electrode in the left hemisphere prompted his patients to report conscious experiences of touch on the right side of the body; stimulating the right hemisphere led to feelings of touch on the left side of the body.13 The correlation is systematic: nearby points on the gyrus correspond to nearby points on the body, and regions of the body that are more sensitive, such as the lips and fingertips, occupy more real estate on the gyrus. Stimulate the gyrus near the middle of the brain, and you feel it in your toes. Slide the electrode along the gyrus, stimulating at ever more lateral points, and the feeling, with a few exceptions, slides systematically up the body. The exceptions are interesting. The face, for instance, resides next to the hand on the gyrus. The toes are next to the genitals—a fact perhaps relevant to foot fetishes, as V. S. Ramachandran has suggested.14