Detailed Structure of the Cortical Magnetic Response to Words

We measured magnetic cortical response to words and analyzed its variability in individual trials. Considerable variations of the amplitudes of different components of the response in different trials suggest hopping of active spot from one point to another within a cortical area responsible for a certain processing stage. This behavior is similar to that observed in experiments with voluntary movement. We believe that only a small fraction of cortical area involved in a certain neural function is active during any particular trial. Next time another spot in the area will be activated. This is the reason of high variability of magnetic signals which are extremely sensitive to the position of the active spot on the folded cortical surface.