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 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.^[1]

Discovery

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.^[2]

The possibility to do research on electrical brain potentials preceding voluntary movements came with the advent of the 'computer of average transients,' the first, primitive 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.^[3] After detailed investigation and control experiments such as passive finger movements the Citation Classic with the term Bereitschaftspotential was published.^[1]

Mechanism

Typical recording of a Bereitschaftspotential

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 [citation needed].

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.^[4] 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.^[5] 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.^[6]

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.^[7] 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.

Another ERP component which was discovered in 1964 is the contingent negative variation, or CNV.^[8] 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. Other researchers have shown that they can be disassociated.^[9]

Outcomes

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”.^[10] The interest was even greater in psychology and philosophy because volition is traditionally associated with human freedom (cf. Kornhuber 1984).^[11] 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.^[12] 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.^[13] The BP has preciptated a worldwide discussion about free will (cf. the closing chapter in the recent book "The Bereitschaftspotential").^[14]

EEGs and EMGs are used in combination with Bayesian inference to construct Bayesian networks which attempt to predict general patterns of Motor Intent Neuron Action Potentials firing. Researchers attempting to develop non-intrusive brain-machine interfaces are interested in this, as are system analysis, operations research, and epistemology (e.g. the Smith predictor has been suggested in the discussion). (explanation needed!)

BP and free will

In a series of experiments in the 1980s, Benjamin Libet studied the relationship between conscious experience of volition and the BP e.g.^[15] and found that the BP started about 0.35 sec earlier than the subject's reported conscious awareness that 'now he or she feels the desire to make a movement.' Libet concludes that we have no free will in the initiation of our movements; though, since subjects were able to prevent intended movement at the last moment, we do have a veto.

These studies have provoked widespread debate.^[16] See also the recent extensive critique by Klemm, 2010).^[17]

Applications

An interesting use of the Bereitschaftspotential is in Brain-Computer Interface (BCI) applications; this signal feature can be identified from scalp recording (even from single-trial measurements) and interpreted for various uses, for example control of computer displays or control of peripheral motor units in spinal cord injuries.^[18]

References

1. ^ ^{a b} Kornhuber, H.H.; Deecke, L. (1965). Hirnpotentialänderungen bei Willkürbewegungen und passiven Bewegungen des Menschen: Bereitschaftspotential und reafferente Potentiale. Pflügers Arch 284: 1–17 "Citation Classic".
2. ^ Kornhuber, H.H.; Deecke, L. (1990). Readiness for movement – The Bereitschaftspotential-Story, Current Contents Life Sciences 33, 4 Citation Classics January 22: 14. [1]
3. ^ Kornhuber, H.H.; Deecke, L. (1964). Hirnpotentialänderungen beim Menschen vor und nach Willkürbewegungen, dargestellt mit Magnetbandspeicherung und Rückwärtsanalyse. Pflügers Arch Eur J Physiologie 281: 52.
4. ^ Deecke, L.; Grözinger, B.; Kornhuber H.H. (1976). Voluntary finger movement in man: Cerebral potentials and theory. Biol Cybern 23: 99–119.
5. ^ Grözinger, B.; Kornhuber, H.H.; Kriebel, J.; Szirtes, J.; Westphal, K.T.P. (1980). The Bereitschaftspotential preceding the act of speaking. Also an analysis of artifacts. pp 798–804 in Kornhuber H.H., Deecke L., eds., Motivation, motor and sensory processes of the brain: Electrical potentials, behaviour and clinical use. Progr Brain Res 54, Amsterdam, Elsevier.
6. ^ Huckabee, M.L.; Deecke, L.; Cannito, M.P.; Gould, H.J.; Mayr, W. Cortical control mechanisms in volitional swallowing: the Bereitschaftspotential. Brain Topogr. 16: 3–17 (2003).
7. ^ Deecke, L; Weinberg, H.; Brickett, P. (1982). Magnetic fields of the human brain accompanying voluntary movement. Bereitschaftsmagnetfeld. Exp. Brain Res. 48: 144–148.
8. ^ Walter, W.G; Cooper, R.; Aldridge, V.J.; McCallum, W.C.; Winter, A.L. (1964). Contingent Negative Variation: an electric sign of sensorimotor association and expectancy in the human brain. Nature 203: 380-384.
9. ^ Tecce, J.J. (1972). Contingent negative variation (CNV) and psychological processes in man. Psychological Bulletin 77: 73-108.
10. ^ Eccles, J.C.; Zeier, H. (1980) Gehirn und Geist. Zürich, Kindler.
11. ^ Kornhuber, H.H. (1984). Von der Freiheit pp 83–112 in Lindauer M, Schöpf A, eds., Wie erkennt der Mensch die Welt? Grundlagen des Erkennens, Fühlens und Handelns. Geistes und Naturwissenschaftler im Dialog. Ernst Klett Stuttgart.
12. ^ Heckhausen, H. (1987). Perspektiven einer Psychologie des Wollens. pp 121–142 in Heckhausen, H. et al., eds., Jenseits des Rubikon: Der Wille in den Humanwissenschaften. Springer, Berlin.
13. ^ Deecke, L; Kornhuber, H.H. (1978). An electrical sign of participation of the mesial “supplementary” motor cortex in human voluntary finger movement. Brain Res 159: 473–476.
14. ^ Deecke, L.; Kornhuber, H.H. (2003). Human freedom, reasoned will, and the brain. The Bereitschaftspotential story. In: M Jahanshahi, M Hallett (Eds.) The Bereitschaftspotential, movement-related cortical potentials. Kluwer Academic / Plenum Publishers [ISBN 0-306-47407-7] pp. 283–320.
15. ^ Libet, B. (1985) Unconscious cerebral initiative and the role of conscious will in voluntary action. Behav & Brain Sci 8: 529–566.
16. ^ Lavazza, A.; De Caro, M. (2010). Not so fast. On some bold neuroscientific claims concerning human angency. Neuroethics 3: 23-41. [DOI 10.1007/s12152-009-9053-9]
17. ^ Klemm, W. R. 2010 Free will debates: simple experiments are not so simple. "Advances in Cognitive Psychology,6: 47-65.
18. ^ Wang, Y.; Zhang, Z.; Li, Y.; Gao, X.; Gao, S.; Yang, F. (2004). BCI competition 2003-data set IV: An algorithm based on CSSD and FDA for classifying single-trial EEG. IEEE Transactions on Biomedical Engineering 51(6): 1081–1086.

Further reading

• Deecke, L.; Kornhuber, H.H. (2003). Human freedom, reasoned will, and the brain. The Bereitschaftspotential story. In: M Jahanshahi, M Hallett (Eds.) The Bereitschaftspotential, movement-related cortical potentials. Kluwer Academic / Plenum Publishers [ISBN 0-306-47407-7] pp. 283–320.
• Kornhuber HH; Deecke L (2007) Wille und Gehirn [will and the brain]. Edition Sirius. Bielefeld/Locarno. 149 pp [ISBN 987-3-89528-628-5]

External links

• http://www.cmds.canterbury.ac.nz/documents/huckabee_swallowing.pdf
• http://www.cs.washington.edu/homes/rao/shenoy_rao05.pdf
• MeSH Bereitschaftspotential

See also

• Epiphenomenalism
• Somatosensory evoked potential
• C1 and P1
• Visual N1
• Mismatch negativity
• N100
• N200
• N2pc
• N170
• P200
• N400
• P300 (neuroscience)
• P3a
• P3b
• Late Positive Component
• Difference due to Memory
• Contingent negative variation
• Error-related negativity
• Lateralized readiness potential
• Early left anterior negativity
• P600