Bereitschaftspotential

In neurology, the Bereitschaftspotential or BP (from German, 'readiness potential'), also called the pre-motor potential or readiness potential (RP), is a measure of activity in the motor cortex and supplementary motor area of the brain leading up to voluntary muscle movement. The BP is a manifestation of cortical contribution to the pre-motor planning of volitional movement. It was first recorded and reported in 1964 by Hans Helmut Kornhuber and Lüder Deecke at the University of Freiburg in Germany. In 1965 the full publication appeared after many control experiments. In neurology, the Bereitschaftspotential or BP (from German, 'readiness potential'), also called the pre-motor potential or readiness potential (RP), is a measure of activity in the motor cortex and supplementary motor area of the brain leading up to voluntary muscle movement. The BP is a manifestation of cortical contribution to the pre-motor planning of volitional movement. It was first recorded and reported in 1964 by Hans Helmut Kornhuber and Lüder Deecke at the University of Freiburg in Germany. In 1965 the full publication appeared after many control experiments. In the spring of 1964 Hans Helmut Kornhuber (then docent and chief physician at the department of neurology, head Professor Richard Jung, university hospital Freiburg im Breisgau) and Lüder Deecke (his doctoral student) went for lunch to the 'Gasthaus zum Schwanen' at the foot of the Schlossberg hill in Freiburg. Sitting alone in the beautiful garden they discussed their frustration with the passive brain research prevailing worldwide and their desire to investigate self-initiated action of the brain and the will. Consequently, they decided to look for cerebral potentials in man related to volitional acts and to take voluntary movement as their research paradigm. The possibility to do research on electrical brain potentials preceding voluntary movements came with the advent of the 'computer of average transients' (CAT computer), invented by Manfred Clynes, the first still simple instrument available at that time in the Freiburg laboratory. In the electroencephalogram (EEG) little is to be seen preceding actions, except of an inconstant diminution of the α- (or μ-) rhythm. The young researchers stored the electroencephalogram and electromyogram of self-initiated movements (fast finger flexions) on tape and analyzed the cerebral potentials preceding movements time-reversed with the start of the movement as the trigger, literally turning the tape over for analysis since they had no reversal playback or programmable computer. A potential preceding human voluntary movement was discovered and published in the same year. After detailed investigation and control experiments such as passive finger movements the Citation Classic with the term Bereitschaftspotential was published. The BP is ten to hundred times smaller than the α-rhythm of the EEG; only by averaging, relating the electrical potentials to the onset of the movement it becomes apparent. Figure shows the typical slow shifts of the cortical DC potential, called Bereitschaftspotential, preceding volitional, rapid flexions of the right index finger. The vertical line indicates the instant of triggering t = 0 (first activity in the EMG of the agonist muscle). Recording positions are left precentral (L prec, C3), right precentral (R prec, C4), mid-parietal (Pz); these are unipolar recordings with linked ears as reference. The difference between the BP in C3 and in C4 is displayed in the lowest graph (L/R prec). Superimposed are the results of eight experiments as obtained in the same subject (B.L.) on different days. see Deecke, L.; Grözinger, B.; Kornhuber H.H. (1976) Note that the BP has two components, the early one (BP1) lasting from about −1.2 to −0.5; the late component (BP2) from −0.5 to shortly before 0 sec. The pre-motion positivity is even smaller, and the motor-potential which starts about fifty to sixty milliseconds before the onset of movement and has its maximum over the contralateral precentral hand area is still smaller. Thus, it takes great care to see these potentials: exact triggering by the real onset of movement is important, which is especially difficult preceding speech movements. Furthermore, artifacts due to head-, eye-, lid-, mouth-movements and respiration have to be eliminated before averaging because such artifacts may be of a magnitude which makes it difficult to render them negligible even after hundreds of sweeps. In the case of eye movements eye muscle potentials have to be distinguished from cerebral potentials. In some cases animal experiments were necessary to clarify the origin of potentials such as the R-wave. Therefore, it took many years until some of the other laboratories were able to confirm the details of Kornhuber & Deecke's results. In addition to the finger or eye movements as mentioned above, the BP has been recorded accompanying willful movements of the wrist, arm, shoulder, hip, knee, foot and toes. It was also recorded prior to speaking, writing and also swallowing. The magnetoencephalographic (MEG) equivalent of the Bereitschaftspotential (BP), 'Bereitschafts(magnetic)field' (BF), or readiness field (RF) was first recorded in Hal Weinberg's laboratory at Simon Fraser University Burnaby B.C. Canada in 1982. It was confirmed that the early component, BP 1 or BF1, respectively was generated by the supplementary motor area (SMA), including the pre-SMA, while the late component, BP2 or BF2, was generated by the primary motor area, MI. A very similar – and equally important – event-related potential (ERP) component had earlier been discovered by the British neurophysiologist William Grey Walter in 1962 and published in 1964. It is the contingent negative variation (CNV). The CNV also composes two waves; the initial wave (i.e., O wave) and the terminal wave (i.e., E wave). The terminal CNV has similar characteristics as the BP and many researchers have claimed that the BP and the terminal CNV are the same component. At least there is a consensus that both indicate a preparation of the brain for a following behavior. The Bereitschaftspotential was received with great interest by the scientific community, as reflected by Sir John Eccles's comment: 'There is a delightful parallel between these impressively simple experiments and the experiments of Galileo Galilei who investigated the laws of motion of the universe with metal balls on an inclined plane'. The interest was even greater in psychology and philosophy because volition is traditionally associated with human freedom (cf. Kornhuber 1984). The spirit of the time, however, was hostile to freedom in those years; it was believed that freedom is an illusion. The tradition of behaviourism and Freudism was deterministic. While will and volition were frequently leading concepts in psychological research papers before and after the first world war and even during the second war, after the end of the second world war this declined, and by the mid-sixties these key words completely disappeared and were abolished in the thesaurus of the American Psychological Association. The BP is an electrical sign of participation of the supplementary motor area (SMA) prior to volitional movement, which starts activity prior to the primary motor area. The BP has precipitated a worldwide discussion about free will (cf. the closing chapter in the book 'The Bereitschaftspotential'). As said above, the activity of the SMA generates the early component of the Bereitschaftspotential (BP1 or BP early). The SMA has the starting function of the movement or action. The role of the SMA was further substantiated by Cunnington et al. 2003, showing that SMA proper and pre-SMA are active prior to volitional movement or action, as well as the cingulate motor area (CMA). This is now called ‘anterior mid-cingulate cortex (aMCC)’. Recently it has been shown by integrating simultaneously acquired EEG and fMRI that SMA and aMCC have strong reciprocal connections that act to sustain each other’s activity, and that this interaction is mediated during movement preparation according to the Bereitschaftspotential amplitude.