Has neuroscience disproven free will?

28th Apr 2020

Neuroscientific investigations into free will have centered on the readiness potential (RP): a negative build-up of electrical potential preceding self-initiated movement [1]. The classic interpretation of the RP is that it reflects movement preparation processes for self-initiated acts [2]. In a seminal paper, Libet and colleagues found that the onset of the RP preceded the reported time at which subjects became aware of their intention to act [3]. They concluded that unconscious brain processes determine our decisions long before we become consciously aware of them, which has been used to argue that free will is an illusion.

However, much research has since been conducted on this topic, with some concluding that Libet’s findings do not seriously threaten free will [4,5]. This is due to criticisms of the experimental task – such as a lack of ecological validity [6], generalisability [6], and internal validity [7,8,9] – as well as findings that humans are able to veto a decision until the very last moments before an action is completed, even if movement has already begun and a RP is present [10]. Other arguments against Libet’s conclusion stem from alternative interpretations of the RP.

Two such models with alternative interpretations are the stochastic accumulator model [11,12] and the slow cortical potential sampling hypothesis [13]. Despite differences between these models, they both argue that the early part of the RP (from its onset until a few hundred milliseconds before movement) does not reflect unconscious movement preparation processes. Instead, the decision to act is said to occur very late in the time course of the RP, close to the reported time of awareness of intention. Hence, Libet’s conclusion, based on the classic interpretation of the RP, that unconscious processes determine our decisions far in advance of our conscious awareness is challenged.

As for the brain areas involved in this process, the early RP is thought to originate in the supplementary motor area (SMA), pre-SMA, and anterior mid-cingulate cortex [14-21]. These areas may be connected, via the basal ganglia, to the primary motor cortex [22], where activity in the hemisphere contralateral to movement is associated with the late RP [23].

Recent neuroscientific evidence has greatly weakened Libet’s conclusion which challenged out intuition of free will, in thanks to criticisms of the experimental task, knowledge of our ability to veto decisions, and alternative interpretations of the RP. Therefore, it can be strongly argued that neuroscience has not disproven free will.

References

[1]        Kornhuber, H. H., & Deecke, L. (1965). 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), 1-17.

[2]        Kornhuber, H. H., & Deecke, L. (1990). Readiness for movement—the Bereitschafts potential-story. Current Contents Life Sciences, 33(4), 14.

[3]        Libet, B., Gleason, C. A., Wright, E. W., & Pearl, D. K. (1993). Time of conscious intention to act in relation to onset of cerebral activity (readiness-potential). Brain, 106, 623-642.

[4]        Brass, M., Furstenberg, A., & Mele, A. R. (2019). Why neuroscience does not disprove free will. Neuroscience & Biobehavioral Reviews, 102, 251-263.

[5]        Maoz, U., Mudrik, L., Rivlin, R., Ross, I., Mamelak, A., & Yaffe, G. (2015). On reporting the onset of the intention to move. In A. R. Mele (Ed.), Surrounding free will: Philosophy, psychology, neuroscience (pp. 184-202). New York, NY: Oxford University Press.

[6]        Mele, A. R. (2014). Free: Why science hasn't disproved free will. Oxford University Press.

[7]        Banks, W. P., & Isham, E. A. (2009). We infer rather than perceive the moment we decided to act. Psychological science, 20(1), 17-21.

[8]        Matsuhashi, M., & Hallett, M. (2008). The timing of the conscious intention to move. European Journal of Neuroscience, 28(11), 2344-2351.

[9]        Rigoni, D., Brass, M., & Sartori, G. (2010). Post-action determinants of the reported time of conscious intentions. Frontiers in Human Neuroscience, 4, 38.

[10]      Schultze-Kraft, M., Birman, D., Rusconi, M., Allefeld, C., Görgen, K., Dähne, S., Blankertz, B., & Haynes, J. D. (2016). The point of no return in vetoing self-initiated movements. Proceedings of the National Academy of Sciences, 113(4), 1080-1085.

[11]      Schurger, A., Sitt, J. D., & Dehaene, S. (2012). An accumulator model for spontaneous neural activity prior to self-initiated movement. Proceedings of the National Academy of Sciences, 109(42), E2904-E2913.

[12]      Schurger, A. (2018). Specific relationship between the shape of the readiness potential, subjective decision time, and waiting time predicted by an accumulator model with temporally autocorrelated input noise. Eneuro, 5(1).

[13]      Schmidt, S., Jo, H. G., Wittmann, M., & Hinterberger, T. (2016). ‘Catching the waves’–slow cortical potentials as moderator of voluntary action. Neuroscience & Biobehavioral Reviews, 68, 639-650.

[14]      Ball, T., Schreiber, A., Feige, B., Wagner, M., Lücking, C. H., & Kristeva-Feige, R. (1999). The role of higher-order motor areas in voluntary movement as revealed by high-resolution EEG and fMRI. Neuroimage, 10(6), 682-694.

[15]      Cui, R. Q., & Deecke, L. (1999). High resolution DC-EEG analysis of the Bereitschaftspotential and post movement onset potentials accompanying uni-or bilateral voluntary finger movements. Brain topography, 11(3), 233-249.

[16]      Cui, R. Q., Huter, D., Lang, W., & Deecke, L. (1999). Neuroimage of voluntary movement: topography of the Bereitschaftspotential, a 64-channel DC current source density study. Neuroimage, 9(1), 124-134.

[17]      Cunnington, R., Windischberger, C., Deecke, L., & Moser, E. (2002). The preparation and execution of self-initiated and externally-triggered movement: a study of event-related fMRI. Neuroimage, 15(2), 373-385.

[18]      Cunnington, R., Windischberger, C., Deecke, L., & Moser, E. (2003). The preparation and readiness for voluntary movement: a high-field event-related fMRI study of the Bereitschafts-BOLD response. Neuroimage, 20(1), 404-412.

[19]      Erdler, M., Beisteiner, R., Mayer, D., Kaindl, T., Edward, V., Windischberger, C., Lindinger, G., & Deecke, L. (2000). Supplementary motor area activation preceding voluntary movement is detectable with a whole-scalp magnetoencephalography system. Neuroimage, 11(6), 697-707.

[20]      Fried, I., Mukamel, R., & Kreiman, G. (2011). Internally generated preactivation of single neurons in human medial frontal cortex predicts volition. Neuron, 69(3), 548-562.

[21]      Nguyen, V. T., Breakspear, M., & Cunnington, R. (2014). Reciprocal interactions of the SMA and cingulate cortex sustain premovement activity for voluntary actions. Journal of Neuroscience, 34(49), 16397-16407.

[22]      Kornhuber, H. H., & Deecke, L. (2012). The Will and Its Brain: An Appraisal of Reasoned Free Will. Lanham, MD: University press of America.

[23]      Shibasaki, H., & Hallett, M. (2006). What is the Bereitschaftspotential?. Clinical neurophysiology, 117(11), 2341-2356.