[Two components in bereitschaftspotential]

In this work the BP onsettimes of voluntary movement and instructed movement were compared. Our results show that there is no significant difference (P > 0.05) between BP onsettimes of the two kinds of movement and that BP occurs before the instruction of movement. The early component of BP, i.e. the negative wave before the presentation of instruction, had no relationship with movement preparation. For the analysis of the source of the BP early component, the BP onsettimes of unconscious eyeblink and instructed eyeblink or self-initiated voluntary eyeblink were compared. It was found that the BP onsettime of unconscious eyeblink was much shorter than that of the two kinds of conscious (P < 0.05) eyeblink. These results suggest that the BP early component is elicited by psychological factors, rather than the result of the preparatory processes of movements in the brain.