Fig. 1.

A) Segment of co-registered EEG (top) and EMG (bottom) traces. A jerk is visible as muscle bursts in the EMG traces; the corresponding EEG traces are affected by movement artifact. B) Jerk-locked back-averaging of many segments results in a visual representation of the association in time between cortical activity at the vertex (Cz) and the jerky movement (EMG). In this case, a Bereitschaftspotential is visible, characterised by a slowly rising negative deflection over the vertex within 2 s before movement onset. C) Visual representation of the negative deflection (in blue) over the vertex 400 ms before movement onset. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)