Averaged and single-trial analysis of cortical activation sequences in movement preparation, initiation, and inhibition

We compare estimates of three-dimensional brain activity extracted from averaged and from selected single-trial magnetoencephalographic signals, in order to study activation sequences related to motor preparation, inhibition, and movement, cued on two tones (S1 and S2). We studied all possible hand-ear combinations in a right-handed subject in both initiation and inhibition, and found some marked differences between combinations. Averaging revealed activity in the right motor cortex in all combinations requiring movement inhibition, irrespective of laterality of finger and ear, and in the contralateral motor cortex during movement (but considerably reduced for the task with the practiced ear and finger). These activation patterns are seen in single trials with variability of latency but not position. In the average signal, a long silent period between the warning and imperative stimuli is seen; in single trials, however, recurring sequences of activation linking frontal and posterior areas are seen throughout the analysis period in all combinations. These results show that single-trial analysis is needed to understand all the significant neural correlates of this task.