brain electric activity map (BEAM), a topographic map of the brain created by a computer that is able to respond to the electric potentials evoked in the brain by a flash of light. Potentials recorded at 4-msec intervals are converted into a many-colored map of the brain, showing them to be positive or negative. The waves may be observed traveling through the brain. If the wave is disordered, blocked, too small, or too large, a tumor or other lesion may be causing the abnormal pattern.
