Bereitschaftspotential

The readiness potential is an electrophysiological measurable phenomenon that in certain areas of the cerebral cortex occurs before voluntary movements ( in supplementärmotorischen cortex) and is interpreted as the expression of activation and preparation processes.

The first description was in the sixties of the 20th century by the German brain researcher Hans Helmut Kornhuber and Deecke Lueder. When allowed to run subjects spontaneous finger movements and drew a continuous DC EEG, so more than one second before execution of the motion showed a characteristic negative potential wave, especially in the frontal and parietal derivations. The proof of these so-called readiness potential or readiness potential waves changed the understanding of the neural processing of motor programs is essential.

Since the readiness potential is weak with a measurable voltage of up to 20 microvolts, compared to other brain activity, it can not just be measured at the time of its occurrence and evaluated, but must be averaged over a number of test runs. The subjects in the famous Libet experiments had to repeat about forty times the same operation. Information about the time at which the potential occurs, therefore, are always averages.

About 500 ms before the start of an arbitrary movement a potential rise is already measurable, the desire for action of a subject is perceived, however, only about 200 ms prior to this. This time was determined by the subjects considered rotating hands of a clock during an EEG measurement. Were now execute a voluntary movement, such as pressing a button, the test subjects, they shared with the position of the watch to the time when they became aware of the desire to act. To determine the individual time lag of the individual persons in describing the position of the clock hand, control experiments were performed in which the subjects were asked to tell the position of the pointer during a timed stimulus of the skin.

This fact confirms to some interpretations, the assumption that free will is an illusion, because the desire to perform a spontaneous movement, only arises after long preparation for this movement. As has been experimented in experiments with only small movements, but it is questionable whether the results can be generalized also to think and want to record.

However, Libet writes the consciousness to a right of veto, which is able to 200-100 ms before the act - to about the amplitude of the readiness potential - still cancel a prepared movement in the short term. The subjects can thus de facto or suppress the motor act.

More recent experiments

The New Zealand researchers Trevena and Miller came after a series of experiments to the initial potential to the conclusion that it makes no difference whether the movement is carried out or is not running. The non-action preceding EEG signatures could not be distinguished from the potentials preceded action. The readiness potentials were " obviously non-specific for the movement preparation " It follows " that the Libet experiments constitute a proof that voluntary movements are initiated unconsciously. " For Felix Hasler, in his book "Neuro mythology " are thus " the ominous readiness potential final demystified ".