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. In mice missing the gene for this protein, ephrin-A5, the sensory body map on the brain's cortex was warped such that some body parts occupied an expanded territory while others were cramped together in smaller areas.
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. His group has not yet analyzed how the mice's distorted body map affects them, but he says it is not too much of a stretch to think that changing the scale of representation in an animal's cortex will also change its behavior.