Next week I will attend a panel about Free Will, in which a group of neuroscientists, physicists and philosophers from Harvard University and MIT will tackle questions like: What is free will? Does it exist? If so, how is it generated? Do animals have free will? How can one make moral decisions without free will? I have always been intrigued by this topic, especially from the neuroscience perspective, and here I would like to give an overview of the concept of free will and its relationship with neuroimaging and neuromodulation techniques.
Free will, understood as the ability to choose between different possible courses of action, has long been a topic of debate among neuroscientists, philosophers and mathematicians. We take for granted that in our daily life we have free will, that what we do from moment to moment is determined by conscious decisions that we freely make. You get out of bed, you go for a walk, you eat vanilla ice cream. It seems that we’re in control of actions like these; so we assume we have free will. But in recent years, some have argued that free will is an illusion, pleading the determinist perspective, which holds that every physical event is predetermined, or completely caused by prior events, or by physics laws, or simply by our genes.
There are several philosophical and scientific arguments against free will, including one based on Benjamin Libet’s famous neuroscientific experiments [1], which allegedly showed that our conscious decisions are caused by neural events that occur before we choose.
In that sense, neuroimaging techniques such as EEG and fMRI can help us understand if all the reasons we think we’ve made a decision for are actually just after-the-fact rationalizations. For example, fMRI machine learning of brain activity (known as multivariate pattern analysis) has been used to predict the user choice of a button (left/right) up to 7 seconds before their reported decision to do so [2]. Multivariate pattern analysis using EEG has also suggested that decisions could be predicted by neural activity immediately after stimulus perception [3].
Furthermore, it has also been suggested that the sense of authorship can be manipulated using neuromodulation techniques. For example, some research suggests that Transcranial Magnetic Stimulation (TMS) can be used to manipulate the perception of which hand a subject wants to move, even though the experience of free will remains intact [4]. In a follow-up experiment in 2015 a team of researchers from the UK and the US published another paper demonstrating that motor responses and the choice of which hand to move can also be modulated using transcranial Direct Current Stimulation (tDCS) [5].
There are other experts in the field, such as Mark Balaguer, who think that anti-free-will arguments put forward by philosophers, psychologists, and neuroscientists don’t provide any good reason to doubt the existence of free will, but this doesn’t necessarily mean that we have free will. From their point of view, the question of whether we have free will remains an open one; we simply don’t know enough about the brain to answer it definitively and therefore we need to keep pushing forward the limits of the field to understand how this intriguing organ works.
- [1] Libet, Benjamin (1985). “Unconscious cerebral initiative and the role of conscious will in voluntary action”(PDF). The Behavioral and Brain Sciences. 8: 529–566.
- [2] Soon, Chun Siong; Brass, Marcel; Heinze, Hans-Jochen; Haynes, John-Dylan (2008). “Unconscious determinants of free decisions in the human brain”.Nature Neuroscience. 11(5): 543–5
- [3] Bode, S.; Sewell, D. K.; Lilburn, S.; Forte, J. D.; Smith, P. L.; Stahl, J. (2012). “Predicting Perceptual Decision Biases from Early Brain Activity”. Journal of Neuroscience. 32(36): 12488–12498
- [4] Brasil-Neto, J P; Pascual-Leone, A; Valls-Sole, J; Cohen, L G; Hallett, M (1992).“Focal transcranial magnetic stimulation and response bias in a forced-choice task”. Journal of Neurology, Neurosurgery & Psychiatry. 55(10): 964–6.
- [5] Javadi, Amir-Homayoun; Beyko, Angeliki; Walsh, Vincent (2015). “Transcranial Direct Current Stimulation of the Motor Cortex Biases Action Choice in a Perceptual Decision Task”. Journal of Cognitive Neuroscience. 27(11): 2174–85.