Readiness potential

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Derivatives of the standby potential on three electrodes and the difference between the first two at the bottom

The readiness potential is an electrophysiologically measurable phenomenon that occurs shortly before voluntary movements in certain areas of the cerebral cortex (in the supplementary motor cortex ) and is interpreted as an expression of activation and preparation processes. It is one of the event-related potentials .

Research context

The readiness potential (BP) belongs together with the contingent negative variation (CNV) to the group of the slow anticipatory potentials ( Anticipatory Slow Waves ). Anticipatory (literally: anticipatory) here means preceding and denotes "potentials that arise before a measurable behavioral performance".

CNV was discovered in 1962 by the British neurophysiologist William Gray Walter and published in the journal Nature in 1964 by his research group . The BP was discovered in 1964 by the German brain researchers Hans Helmut Kornhuber and Lüder Deecke and published in a specialist article in 1965.

While the Contingent Negative Variation (CNV) as a brain potential between two stimuli - stimulus 1 (S1) and stimulus 2 (S2) - from the EEG in a normal way, i.e. H. in the direction of time, which can be averaged (averaging), the readiness potential (BP) discovered by Kornhuber and Deecke arises endogenously in the brain of a test person without direct external stimulus, the self-initiated voluntary movements after previous instruction by the experimenter, the movements at irregular intervals and from free Will to make executes. A self-initiated movement is an unpredictable event, and a potential correlated with it cannot therefore normally, i. H. in time direction, can be averaged from the EEG, because you cannot trigger on an unpredictable internal event. In order to still be able to make a potential that might exist here (the later so-called readiness potential) visible, the authors developed a new technique especially for this purpose: They saved the signals of the experiment (with EEG channels and trigger signals = start of movement) on magnetic tape and then played it Tape in reverse time direction, d. that is, they sent the electrical data against the time direction through the averaging computer. This process is called back-averaging . In this case, the trigger (start of movement) comes first and then the brain potentials, which actually preceded the start of movement (trigger) in the real experiment. So the BP is different from the CNV. At the BP, the test person acts independently, namely on their own initiative (by prior arrangement). In the CNV, the test person acts on direct request, as in sport on the "lot" with the signal sequence "done - go" (with variable intermediate time). The CNV is created between “done” and “go”. Therefore, the CNV was by their discoverers an expectation ( expectancy ) - on the "Go" Wait - allocated while the BP by their discoverers a willingness ( readiness ) - was assigned - to act.

If the time interval between warning stimulus (S1) and target stimulus (S2) is long enough (> 3 s), the CNV can be divided into two components. Immediately after the warning stimulus, the EEG signal is negated early. This early CNV (400 ms - 1500 ms) is interpreted as processing the warning stimulus itself. Because of the orientation reaction that goes with it , it is sometimes referred to as the O wave (orientation wave ). After the signal has flattened to the baseline (1500 ms - 2600 ms), the signal is then negated for a second time. This late CNV (2600 ms - 3700 ms) is attributed to the expectation ( anticipation ) of the target stimulus, which is why it is sometimes referred to as the E-wave (expectation wave ). It is assigned to preparatory processes for the motor response to the expected target stimulus. Functionally, the late CNV is also understood as the sum of two sub-components. The Stimulus-Preceding Negativity (SPN) describes the negation of the EEG signal in anticipation of an information-laden stimulus (feedback or cue stimulus). It occurs independently of the task. However, if the task also includes executing a specific movement in response to a target stimulus, the Movement-Preceding Negativity (MPN) can also be observed as a second sub-component.

In spite of all the differences in the experimental process and in some cases in the underlying brain activity - which was only explored in more detail later - CNV and BP have in common that they indicate behavior-related brain activity before the conscious experience of the corresponding behavior. Because of this, both discoveries had an enormous and lasting impact on subsequent brain research.

Electroencephalography

To record the BP, Kornhuber and Deecke had the test subjects perform spontaneous finger movements and recorded a continuous direct current EEG . More than a second before the movement was performed, a characteristic negative potential wave emerged, especially in frontal and parietal leads.

Since the standby potential with a measurable voltage of up to 20 µV is weak compared to other brain activity, it cannot simply be measured and evaluated at the time it occurs, but has to be averaged over a large number of test runs. The subjects in the well-known Libet experiments had to repeat the same process about forty times. Information about time intervals before or after the maximum of the recorded potential are therefore usually average values.

Subjectively experienced decision

A potential increase can already be measured around 500 ms before the start of a voluntary movement. The subjectively experienced decision of a test person for movement is only perceived by the test person approx. 200 ms before this movement. This time was determined by looking at the rotating hand of a clock during an EEG measurement. If the test subjects now wanted to perform a voluntary movement, such as pressing a button, they reported the position of the clock hand at the point in time when they became aware of their decision to act. In order to determine the individual time delay of each person in describing the position of the clock hand, control experiments were carried out in which the test subjects were asked to communicate the position of the pointer to the skin during a timed stimulus.

For some, the Libet experiments and extended follow-up experiments confirmed the assumption that free will is an illusion, since the desire to carry out a spontaneous movement arises only after a neuronal initiation of these movement sequences.

In later publications, Libet himself ascribed the consciously experienced decisions the possibility of a right of veto. This means that a person is able to briefly interrupt a neuronal movement that has already been initiated up to 200-100 ms before the action - up to approximately the maximum amplitude of the standby potential. The test subjects could de facto suppress the motor action. This observation by Libet was impressively confirmed and specified more precisely 31 years later and with the technical possibilities that have since been further developed. A working group led by John-Dylan Haynes in Berlin had test subjects play against their own BP in a kind of computer game. It was shown that they could stop up to 200 ms before a foot movement announced by the BP. The time threshold of 200 ms was referred to as the point of no return .

Experiments on the awareness of voluntary decisions by Kühn and Brass from 2009 had already indicated that veto decisions are also made unconsciously and are only seen as free decisions afterwards. The authors of the new report from 2016 explicitly refused in their publication to discuss the question of "free will" in connection with their results.

Origin of the name

In their 1965 publication, Kornhuber and Deecke explained in detail why they did not use the term Contingent Negative Variation (CNV) from Walter's group for the results of their experiments - despite the great similarity in the EEG image. They felt that they could not apply the CNV (expectancy) behavior to their experiments.

“About the terminology: we cannot understand the negative potential of voluntary movements as a wave of expectation, because nothing is expected; rather, the bioelectrical process seems to belong to those brain processes that appear in consciousness as readiness to act (emphasis in the original). "

In the following sentence, however, they again emphasized an important common feature of CNV and their results and put up for discussion whether the assignment "'readiness" would not have been more correct for the CNV as well.

literature

history

  • W. Gray Walter , R. Cooper, VJ Aldridge, WC McCallum, AL Winter: Contingent Negative Variation: An Electric Sign of Sensori-Motor Association and Expectancy in the Human Brain . In: Nature . tape 203 , no. 4943 , July 25, 1964, p. 380-384 , doi : 10.1038 / 203380a0 .
  • Hans Helmut Kornhuber, Lüder Deecke: Changes in brain potential with voluntary movements and passive movements of humans: readiness potential and reacting potentials . In: Pflügers Arch 284, 1965, pp. 1-17. doi: 10.1007 / BF00412364 , researchgate.net (PDF).

Introductions

  • CHM Brunia, GJM van Boxtel, KBE Böcker: Negative Slow Waves as Indices of Anticipation: The Readiness Potential, the Contingent Negative Variation, and the Stimulus-Preceding Negativity . In: Steven J. Luck, Emily S. Kappenman (Eds.): The Oxford Handbook of Event-Related Potential Components . Oxford University Press, USA 2012, ISBN 0-19-537414-2 , p. 189-207.
  • SP Wise: Movement selection, preparation, and the decision to act: neurophysiological studies in nonhuman primates . In: Marjan Jahanshahi, Mark Hallett (Ed.): The Readiness Potential: Movement-Related Cortical Potentials . Kluwer Academic / Plenum Publishers, New York 2003, ISBN 0-306-47407-7 , pp. 249-268.

Others

Individual evidence

  1. ↑ a b Manfred Stöhr, J. Dichgans, Ulrich W. Buettner, CW Hess, Eckart Altenmüller: Evoked Potentials. SEP-VEP-AEP-EKP-MEP . 3. Edition. Springer-Verlag, Berlin 1996, ISBN 3-662-07146-0 , p. 567.
  2. ↑ CHM Brunia, GJM van Boxtel, KBE Böcker: Negative Slow Waves as Indices of Anticipation: The Readiness Potential, the Contingent Negative Variation, and the Stimulus-Preceding Negativity . In: Steven J. Luck, Emily S. Kappenman (Eds.): The Oxford Handbook of Event-Related Potential Components . Oxford University Press, USA 2012, pp. 189-207, ISBN 0-19-537414-2 , pp. 189.
  3. ^ A b Ray Cooper: The discovery of the contingent negative variation (CNV) . In: Current Contents Life Sciences 21, May 27, 1985, upenn.edu (PDF)
  4. ^ W. Gray Walter , R. Cooper, VJ Aldridge, WC McCallum, AL Winter: Contingent Negative Variation: An Electric Sign of Sensori-Motor Association and Expectancy in the Human Brain . In: Nature . tape 203 , no. 4943 , July 25, 1964, p. 380-384 , doi : 10.1038 / 203380a0 .
  5. ↑ a b H. H. Kornhuber, L. Deecke: Readiness for movement - the readiness potential story. In: Current Contents Life Sciences. 33 (4): 14 (1990) and Current Contents Clinical Medicine. 18 (4): 14 (1990), upenn.edu (PDF)
  6. ↑ a b Hans H. Kornhuber, Lüder Deecke: Changes in brain potential during voluntary movements and passive movements of humans: readiness potential and reacting potentials. In: Pflügers Arch 284, 1965, pp. 1-17. doi: 10.1007 / BF00412364 researchgate.net (PDF)
  7. ↑ HH Kornhuber, L. Deecke: Changes in brain potential in humans before and after voluntary movements, shown with magnetic tape storage and backward analysis . Pflügers Arch 281, 52 (1964).
  8. ↑ a b Ingrid Funderud, Magnus Lindgren, Marianne Løvstad, Tor Endestad, Bradley Voytek: Differential Go / NoGo Activity in Both Contingent Negative Variation and Spectral Power . In: PLOS ONE . tape 7 , no. 10 , October 31, 2012, ISSN  1932-6203 , p. e48504 , doi : 10.1371 / journal.pone.0048504 , PMID 23119040 , PMC 3485369 (free full text) - ( plos.org [accessed on August 22, 2018]).
  9. ↑ Luck, Steven J. (Steven John): An introduction to the event-related potential technique . Second ed. MIT Press, Cambridge, Massachusetts 2014, ISBN 978-0-262-32405-2 , pp. 73 .
  10. ↑ Hiroshi Shibasaki, Mark Hallett: What is the Readiness Potential? In: Clinical Neurophysiology , 117, 2006, pp. 2341-2356. ucsf.edu (PDF)
  11. ↑ Gerhard Roth : From the point of view of the brain. Suhrkamp, ​​Frankfurt / M. 2003, ISBN 3-518-58383-2 , p. 486 ff.
  12. ↑ Adina L. Roskies: How Does Neuroscience Affect Our Conception of Volition? In: Annual Review of Neuroscience (2010), 33, pp. 109-130
  13. ^ Benjamin Libet: Unconscious cerebral initiative and the role of conscious will in voluntary action In: Behavioral and Brain Sciences (1985), 8, pp. 529-566
  14. ↑ M. Schultze-Kraft, D. Birman, M. Rusconi, C. Allefeld, K. Görgen, S. Dähne, B. Blankertz, JD Haynes: The point of no return in vetoing self-initiated movements. In: Proceedings of the National Academy of Sciences . Volume 113, number 4, January 2016, pp. 1080-1085, doi: 10.1073 / pnas.1513569112 , PMID 26668390 , PMC 4743787 (free full text).
  15. ^ S. Kühn, M. Brass: Retrospective construction of the judgment of free choice. In: Consciousness and Cognition . Volume 18, number 1, March 2009, pp. 12-21, doi: 10.1016 / j.concog.2008.09.007 , PMID 18952468 .
  16. ↑ Hans H. Kornhuber, Lüder Deecke: Changes in brain potential during voluntary movements and passive movements of humans: readiness potential and reacting potentials. In: Pflügers Arch Physiol 284, 1965, pp. 1-17. doi: 10.1007 / BF00412364 , p. 15, researchgate.net (PDF)