This is a short review of the article detailed below
Schurger, A., Pak, J., & Roskies, A. L. (2021). What is the readiness potential?. Trends in Cognitive Sciences, 25(7), 558-570. https://doi.org/10.1016/j.tics.2021.04.001Â
The volition of human action or free will has been a subject of fascination and debate for centuries. Over the years, traditional philosophers as well as scientists from a range of disciplines have attempted to characterize free will and even question its limitations. This article by Schruger and co (2021) has presented arguments for and against the presence of free will from a neuroscience perspective, primarily quoting Benjamin Libet (1983) who gave the concept of Readiness Potential (RP) as evidence that humans lack free will. This article covers both sides of the argument using evidence from neurocognitive and neurobiological studies and posits a revaluation of the philosophical problem of free will.
The Readiness Potential (RP) is a term that emerged from studies using Electroencephalogram (EEG) and describes a slow negative going electrical potential that is visible right before any self-initiated movements by an individual (Kornhuber & Deeke, 1965). In the first EEG studies on Readiness Potential, Libet (1983) found that there was a distinct negative wave hundreds of milliseconds before participants reported feeling an urge to make motor movements. Liber argued that this unconscious cerebral initiation before any actions undermined human free will as it indicated that our brains initiated action well before we are even aware of it. Schruger et al (2021) question whether this pre movement build-up of neuronal activity has any significance and they provide a number of counter claims.
The RP looks similar to contingent negative variation (CNV) and stimulus preceding negativity (SPN) and have even been seen in studies on decision making rather than voluntary movements (Alexander et al., 2016). Next, they highlight how RP is mostly seen on average of numeral trials and not prominent in single trials where magnitude of noise on EEG readings are much higher (Dirnberger et al., 2008). In studies using single trials, the RPs were indistinguishable from normal brain wave fluctuations (Zeid et al., 2015). RPs were even evident in studies where there was no conscious willing of motor movements further raising doubts of its significance (Schultze et al., 2020). There are also stochastic decision models (SDM) with substantial neurophysiological evidence which posit RPs as neuronal activities even before decision to move has been made rather than after it (Schurger et al., 2012). These accounts support the notion that RPs do not reflect process of planning and preparation of movements. The newer Accumulation-to-Bound Model (AiBM) also supports the late decision position that neuronal changes do not necessarily mean intentional preparation of movements (Schurger et al., 2016). RPs could simply be artefacts of the averaging process and nature of electrophysiological testing. In most instances, the decision to move happens when the threshold of stochastic fluctuation is reached prior to movement and the RPs do not correspond to any significant event as awareness of intention and decision points largely coincide.
The article is a compelling argument against the straightforward notion by Libet (1983) that Readiness Potential indicates inefficiency or absence of intentional will. The authors have provided evidences from a large number of studies that have utilized a range of electrophysiological techniques and experimental paradigms. While they have also provided adequate evidence and insights in line with Libet’s claims, the evidence against it is insurmountable. While RPs are definitely a significant tool and object of study that warrant further examination, the authors conclude that its links to the phenomenon of human free will is a weak one and credible inferences cannot be made about it. As a comprehensive review of research evidence on Readiness Potential from the previous several decades, the article is a compelling argument in considering its alternative interpretations.
References
Alexander, P., Schlegel, A., Sinnott-Armstrong, W., Roskies, A. L., Wheatley, T., & Tse, P. U. (2016). Readiness potentials driven by non-motoric processes. Consciousness and Cognition, 39, 38-47. https://doi.org/10.1016/j.concog.2015.11.011Â
Dirnberger, G., Lang, W., & Lindinger, G. (2008). A new method to determine temporal variability in the period of pre-movement electroencephalographic activity. International Journal of Psychophysiology, 70(3), 165-170. https://doi.org/10.1016/j.ijpsycho.2008.08.006Â
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, 1-17. https://doi.org/10.1007/BF00412364Â
Libet, B. (1983). Time of conscious intention to act in relation to onset of cerebral activity (readiness potential). Brain, 106, 623-642.https://doi.org/10.1093/brain/106.3.623
Schultze, K. M., Parés-Pujolrà s, E., Matić, K., Haggard, P., & Haynes, J. D. (2020). Preparation and execution of voluntary action both contribute to awareness of intention. Proceedings of the Royal Society B, 287(1923), 20192928. https://doi.org/10.1098/rspb.2019.2928Â
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. https://doi.org/10.1073/pnas.1210467109Â
Schurger, A., Mylopoulos, M., & Rosenthal, D. (2016). Neural antecedents of spontaneous voluntary movement: a new perspective. Trends in Cognitive Sciences, 20(2), 77-79. https://doi.org/10.1016/j.tics.2015.11.003Â
Schurger, A., Pak, J., & Roskies, A. L. (2021). What is the readiness potential?. Trends in Cognitive Sciences, 25(7), 558-570. https://doi.org/10.1016/j.tics.2021.04.001Â
Zeid, E. A., & Chau, T. (2015). Electrode fusion for the prediction of self-initiated fine movements from single-trial readiness potentials. International Journal of Neural Systems, 25(04), 1550014. https://doi.org/10.1142/S0129065715500148Â
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