EEG correlates of visual-motor practice in man.

Special analysis of EEG signals was performed for 15 subjects engaged in three motor tasks of differing difficulty. A measure of average weighted coherence (C) was computed between the six possible combinations of four scalp areas: Oz, C3, C4 and Fz. In all subjects, regardless of task, scalp recordings over cortical areas known to have relatively dense fiber connections had significantly greater C values. However, the effects of task difficulty and practice were superimposed upon this basic pattern. Thus, the most difficult task (pursuit-rotor tracking) resulted in the highest coherence levels, while the least difficult task (visual tracking only of the pursuit-rotor disk) resulted in the lowest coherence levels. Practice, on the other hand, was associated with a significant decrease in overall level of coherence. This decrease is consistent with an interpretation of reduced task difficulty due to visual-motor learning. The results of the present study suggest that patterns of scalp EEG coherence may reflect some aspects of the underlying pattern of anatomical pathways, as well as the more dynamic properties of task difficulty and visual--motor practice.