The simple beginnings of volition

Most intellectual breakthroughs seem obvious once the solution is known. This feeling of “I could have done that” or “of course that’s how you’d do it” deceives though, for solutions to problems only appear obvious in hindsight, never in advance.

It’s no different with Kornhuber and Deecke’s seminal 1965 paper, in which they described the readiness potential for the first time. This finding was only possible because they advanced EEG methods such that they could study the neural correlates of spontaneous actions, that is, they could see what happened in the brain when the participants acted out of their own will, not in reaction to any external stimulation. Although this might seem straightforward, there is one inherent problem with neural recordings that makes such a study tricky: noise.

Brain recordings are inherently noisy because any such recording includes lots of brain activity that is entirely unrelated to the task of interest. By averaging across many trials, the noise disappears and we get to see what actually happens in the brain. This requires some way of averaging the data. In experiments where we present something to the participant (e.g., a sound or an image) this can be done easily: when the stimulus is presented, a mark is automatically added to the neuroimaging recording, which we then cut into individual trials, align to said mark, and then average the neural activity for each time point from the stimulus presentation until the end of the trial. For most functions this is not a problem – but how do you average across spontaneous, voluntary decisions?

The problem with voluntary and spontaneous actions is that by definition they are not externally triggered by some sort of stimulation, but come from the participant’s own internal decision, free from any outside forces. So if you want to look at the neural correlates of such spontaneity, you face the problem of having nothing against which to average.

What did Kornhuber and Deecke do then? Participants performed simple actions (e.g., a button press at a time of their own choosing/their own will) that triggered the EEG recording. Thus, when the participant pressed a button, it left a little indication of when the action occurred relative to the neural activity. Kornhuber and Deecke then averaged the neural activity preceding the action by cutting the tape at the moment of the action, reversing it, averaging to the action as if it were a stimulus, and then reversing the tape again to reinstate its initial chronology. Thus, they had the neural activity preceding a spontaneous, not-externally-triggered, action.

Kornhuber & Deecke’s solution is strikingly simple: a button press, an EEG recording, scissors, and two reversals of a magnetic tape – that’s all it took to start the science of volition, the science of spontaneous, voluntary movements. Kornhuber and Deecke barely did anything different from current methods; the sole difference lied in the two reversals of the magnetic tape. And yet, no one had thought of this solution until they did.

The problem with simplicity is that it’s much easier to understand than to use. A simple solution to a complex problem can be understood by most, but only created by few. Create a solution to a complex problem and it looks like an act of genius; create a simple solution to a complex problem and it looks obvious.


PS: Yes, the reverse computation method is described first in a different paper from 1964, but this is almost impossible to find & all credit usually goes to the 1965 paper. For simplicity’s sake I took these two papers as one project under the name of their famous 1965 paper

PPS: Having noticed that many researchers hadn’t read the original article due to not speaking German and there not being any translation, I translated the whole paper from German into English. The translation appeared in the original journal in 2016, with Lüder Deecke’s blessing, and can be found here:



Kornhuber, Hans Helmut, and Lüder Deecke. "Hirnpotentialanderungen beim Menschen vor und nach Willkurbewegungen dargestellt mit Magnetbandspeicherung und Ruckwartsanalyse." PFLUGERS ARCHIV-EUROPEAN JOURNAL OF PHYSIOLOGY. Vol. 281. No. 1. 175 FIFTH AVE, NEW YORK, NY 10010: SPRINGER VERLAG, 1964.

Kornhuber, Hans H., and Lüder Deecke. "Hirnpotentialänderungen bei Willkürbewegungen und passiven Bewegungen des Menschen: Bereitschaftspotential und reafferente Potentiale." Pflüger's Archiv für die gesamte Physiologie des Menschen und der Tiere 284.1 (1965): 1-17.

Kornhuber, Hans H., and Lüder Deecke. "Brain potential changes in voluntary and passive movements in humans: readiness potential and reafferent potentials." Pflügers Archiv-European Journal of Physiology 468.7 (2016): 1115-1124.

Stimulating desires