The Brain That Changes Itself: Stories of Personal Triumph from the Frontiers of Brain Science

by Norman Doidge

Migration of a mental function to the opposite hemisphere can happen because early in development our hemispheres are quite similar, and only later do they gradually specialize. Brain scans of babies in their first year show that they process new sounds in both hemispheres. By age two they usually process these new sounds in the left hemisphere, which has begun to specialize in speech. Grafman wonders whether visual-spatial ability, like language in babies, is initially present in both hemispheres and then inhibited in the left as the brain specializes. In other words, each hemisphere tends to specialize in certain functions but is not hardwired to do so. The age at which we learn a mental skill strongly influences the area in which it gets processed. As infants, we are slowly exposed to the world around us, and as we learn new skills, the most suitable processing sectors of our brains that are as yet uncommitted are the ones used to process those skills.

hemispheric lateralization develops given circumstances rather than hardwired