Changes in the Bereitschaftspotential due to subsequent voluntary autotriggered stimulus

The Bereitschaftspotential (BP) has been studied in two different tasks: simple voluntary isometric flexion/opposition of the thumb and same movement, followed by a mild electrical shock over the median nerve, autotriggered by the movement itself. When the two tasks were organized in separate series, the subject being told about the outcome of the movement beforehand, it was found that: The BP started later; Its amplitude was smaller; The maximum negatively (N2) was smaller, when expecting electrical shock compared to simple voluntary contraction. The decrease was more pronounced over the postcentral areas. When the sequence of the autotriggered electrical shocks was equiprobably intermixed with the simple voluntary presses in single series it was found that virtually no difference existed between different potential measures. This differential influence of equal physical requirements with different subjective sequels upon the potentials related to voluntary movements implied the preferential role of the subject's attitude and state of preparedness upon the brain potentials. Both the elevated stress level and the selective suppression in specific cortical areas might take place in tasks with predictable unpleasant electrical shock.