The sensory homunculus is the familiar textbook caricature of a human being spread out improbably over the surface of the brain. It depicts how much space the brain allocates to our different body parts when it comes to feeling out the world around us. Its wildly uneven proportions are generally thought to arise in response to the activity of sensory neurons feeding information to the brain. In the April Nature Neuroscience, however, researchers led by John Flanagan, HMS associate professor of cell biology, report that a protein previously known to establish maps of the visual world in lower brain centers also plays a prominent role in imprinting a proper body map on the brain's cortex.
Most parents marvel at how their children differ in their interests.
Genetics partly addresses this question by trying to link genes to specific behaviors, such as a propensity for adventurousness. Long-established species differences in sensory maps already reflect differences in functional importance and, by extension, ability. In mice, for example, the whiskers and snout take up most of the sensory brain space, whereas monkey brains dedicate large areas to the hands and feet. Flanagan speculates that in humans genetic variations in how much space the brain devotes to each body part might help explain the difference between an average person and, say, a gifted musician. The current work does not negate the importance of neural activity by incoming neurons to determining brain maps.