The Neuroscience of Free Will
“Consciousness” and “Free Will” are complicated topics. Actually, researchers wish they were merely “complicated” topics – I would go for “staggeringly complex.” “Philosophically and scientifically baffling” has a nice ring to it as well.
There is a two-pronged attack going on in academia in the quest to understand the feeling of “I,” involving both theorists and laboratory neuroscientists. Theorists, like Daniel Dennett or Daniel Wegner, use a wide panoramic lens to peer into the big philosophical conundrums of consciousness and free will. Is the physical brain the engine of the train of experience, and the feeling of “consciousness” merely steam? Or is consciousness the coal driving the brain-engine forward? Is volitional action really caused by our conscious decisions? Or is “deciding” simply an illusion of control superimposed on deterministic biology?
These are huge questions that will likely remain unanswered for years to come.
Neuroscientists prefer to use a microscopic lens to study consciousness and free will. Without losing sight of the big puzzle, they work tirelessly to fit little pieces together, one by one, and their questions are usually pointed and a little more manageable: What is the role of the posterior parietal cortex in the subjective feeling of control? How does the pre-supplementary motor area contribute to voluntary action?
Research on these smaller questions offers much-welcomed relief from philosophy-induced headaches.
The most important aspect of free will is the impression that we consciously control our bodily actions. The official name of this feeling is the “Sense of Agency” (SoA). A basic example of SoA would be my current feeling that, “the words I am typing on this screen are a result of the control I have over the movement of my fingers on the keyboard.” Furthermore, I sense that, “these are not someone else’s fingers, nor do I think that the appearance of words on the screen is a coincidental accident – there is a causal relationship between my typing and the appearance of the words.”
There are two main theories concerning the psychology of SoA — I’ll try to describe them as succinctly as possible:
- The first theory is that we feel SoA because we constantly make predictions about our actions. When these predictions are fulfilled, we perceive that we “willed” the consequences of our actions: If I predict that typing is going to make words appear, and it does, I feel that I caused them to appear.
- The other main theory is that SoA is an illusion, and is experienced after the effects of our actions occur — The motor actions are biologically and subconsciously predetermined, and we only feel that we consciously willed them subsequent to the effects: After noticing that words appear when I type, I assume I willed them to. Because I only feel this after the words appear, my SoA did not cause the actual effect, it just “makes sense” of the whole affair.
Parsing through these heady theories is a tiring process, but if we can quantify aspects of SoA we can make the debate more concrete.
One way that neuroscientists have quantified SoA involves a phenomenon known as the “intentional binding effect.” It goes like this:
Say you have a button in your hand that gives you a small, painless electrical shock exactly one second after you press it. While doing this, you are looking at a timer. At the end of the task you are asked to estimate the time lapse between pressing the button and getting shocked, and you confidently say “a half a second,” though it was actually a full second.
This is the intentional binding effect – when given a task that involves voluntary motor control over a stimulus (i.e. a shock), people’s perception of time is compressed, and they sense a more immediate consequence of their actions than the actual time lapse. The intentional binding effect is used as a marker for SoA because it only occurs when someone has full motor control of a stimulus (i.e. they have complete “agency” over an event), it is consistent across almost all individuals, and it is quantifiable.
New research by Moore et al in the latest Proceedings of the Royal Society sheds some light on the neurological foundations of SoA. Using a technique called “theta-burst stimulation” the researchers were able to temporally “turn-off” specific areas of their human subjects’ brains with bursts of electricity. This was done while they performed the button-pressing shock task described above. Because volitional motor movements are at the heart of SoA, they tested two motor areas – the sensorimotor cortex and the pre-supplementary motor area. While the sensorimotor cortex is responsible for “processing signals directly related to action execution and sensory feedback,” the pre-supplementary motor area is involved in “the preparation and initiation of voluntary actions (Moore et al, 2010).”
The authors found that when they turned-off the sensorimotor cortex there was no effect on intentional binding. That is, the subjects still reported a squished perception of time between pressing the button and feeling the shock. However, when the pre-supplementary motor area was shut down, the subjects no longer perceived a compressed time interval – The pre-supplementary motor area seems to have an effect on SoA while the primary sensorimotor cortex does not.
While this all might seem like run-of-the-mill cognitive neuroscience, the authors put on their theorist caps to show the significance of this result:
“Theoretically, SoA could arise from either of two distinct processes. On the one hand, SoA may involve a prediction—based on the neural commands for action—that the sensory effect will occur. On the other hand, the brain might infer, or postdict, from the conjunction of action and effect, that the action caused the effect, as in illusions of conscious will (Moore et al, 2010, emphasis added).”
Their results point toward the former – the predication-based theory – because the role of the pre-supplementary motor area is the preparation of motor actions, not the sensory feedback that occurs afterward.
In essence, this research scores points for a non-illusory free will. Maybe we have a “sense of agency” because we predict the effects of our actions before we act, and this sense is validated when the predictions are correct.
If you were scared of being a deterministic robot, this work offers some hope.
At the present, my pre-supplementary motor area is preparing me for a walk to the coffee-maker…am I consciously willing my legs to move me through the corridor, or is my mechanic subconscious just pushing me along?