Intersubject variability and intrasubject reproducibility of the bereitschaftspotential

We assessed the intersubject variability and intrasubject reproducibility o f the berritschaftspotential (BP). Twenty healthy volunteers performed exte nsions of their wrist in a self-paced manner every 5-10 seconds. A surface electromyography (EMG) electrode was attached to the wrist extensor group o f the dominant hand to record at least 100 wrist movements, and electroence phalography electrodes were placed over the scalp. Trials were performed at baseline, 15 minutes, 4 hours, and 4 weeks. Measures derived from the BP i ncluded area 1 (-2000 to -650 msec), area 2 (-650-0 msec), total area (area 1 + area 2), amplitude at -650 msec, amplitude at peak negativity prior to EMG onset, and amplitude at 0 msec (trigger). Our findings revealed differ ent variability/reproducibility depending on the particular BP measure bein g analyzed. Using intraclass correlation coefficient (ICC) and concordance correlation coefficient (CCC) as measures of intrasubject reproducibility, area 2, amplitude at peak negativity prior to EMG onset, and amplitude at 0 msec produced the best values. We conclude that in studies that attempt to quantify BP changes before and after an intervention in the same group of subjects, the most reproducible BP measures are those pertaining to the lat e BP component.