Brain waves, impulse control, and free will

In a delightful passage of his book Elbow Room, the philosopher Dan Dennett writes

“The first day I was ever in London, I found myself looking for the nearest Underground station. I noticed a stairway in the sidewalk labeled ‘SUBWAY’, which in Boston is our word for the Underground, so I confidently descended the stairs and marched forth looking for the trains. After wandering about in various galleries and corridors, I found another flight of stairs and somewhat dubiously climbed them to find myself on the sidewalk on the other side of the intersection from where I had started. I must have missed a turn, I thought, and walked back downstairs to try again. After what seemed to me to be an exhaustive search for hitherto overlooked turnstiles or side entrances, I emerged back on the sidewalk where I had started, feeling somewhat cheated. Then at last it dawned on me; I’d been making a sort of category mistake! Searching for the self or the soul can be somewhat like that. You enter the brain through the eye, march up the optic nerve, round and round the cortex, looking behind every neutron, and then, before you know it, you emerge into daylight on the spike of a motor never impulse, scratching your head and wondering where the self is.”

Lift your finger!

Searching for the self through perception raises quizzical questions, but searching for the self through action can leave us dumbfounded. Following Dennett, let’s enter the brain again, but in the opposite direction, that is, through your finger rather than through the eye. Think of what happens in your mind when you carry out the simple act of lifting your index. Typically, it doesn’t feel like much: your finger just goes up. At other times, however, and in particular when you’re thinking about what goes on when you lift your finger, you may come to distinguish between the moment you are intending to lift your finger, and the act itself. What happens during and before that brief interval has been the object of considerable research since the famous experiments of Benjamin Libet and colleagues (1983), who showed that the brain appears to engage in the neural processes that will lead to action well before the moment you feel the intention to act. This finding came as a surprise to many, for it overturns the intuitive perspective we entertain on ourselves as masters of our own domain: It feels like I am intending something, then doing it, but what really happens is that my brain acts, and I am only informed, late and en passant, so to speak, of what’s going on. Libet’s result appears to rob us of our own free will: Not only is what I do caused by the activity of my brain, but also what I intend to do.

None of us are free

But how could it be otherwise? It simply cannot be otherwise, as my mental states are necessarily caused by the activity of the brain. “I” cannot want anything beyond what my brain wants, “I” cannot be different from what the activity of my brain is, in constant interaction with itself, the world, and other people, consists in. Thus, we are looking at a loop that extends between the brain and the brain’s rendering of its own activity. Further, this loop is dynamical — extended both in time and in space. Early, local activity in certain brain regions progressively engage more and more brain regions to become a global brain event that we experience as a conscious state. Different experimental paradigms are catching different aspects and different moments of these neural processes and their subjective renderings, but they all unambiguously converge towards the idea that the mind is ultimately what the brain does.

Reconsidering Libet

With dualistic thoughts out of the way, we can now ask specific questions about the dynamics of decision-making. Schurger et al. (2012, see also Schurger, Mylopoulos & Rosenthal, 2015) recently showed that the gap between early brain activity and our subjective feeling of intending to act is perhaps not as large as Libet’s experiments initially suggested. The slow-rising lateralized readiness potential, the electrical signal that reflects preparation to action and that was (problematically) shown to begin much earlier than people’s own feeling of being about to act, is but a mere artefact, they argue. What happens instead is that random fluctuations in the activity of the brain cross a threshold at some point, and that point is both the moment at which people experience the urge to act and the moment at which they act. This result does not change the conclusion that all mental states are rooted in the brain’s activity, but they give some solace to those who felt it difficult to accept that conscious intentions come almost as a causally inert postdictive reconstruction of what the brain is doing.

Fighting against your own brain

Further, recent results also invite us to reconsider the extent to which we, as agents, have control over our actions. Thus, Schultze-Kraft et al. (2015) showed, using a compelling gamified situation where people fight against their own brain activity through a brain-computer interface system, that one can inhibit the early brain activity that will lead to action, up to about 200ms before the action becomes inevitable. This is Libet’s “free won’t” reinterpreted; arly brain activity that would normally lead to action begins to unfold: I, as an agent, become aware of this unfolding process shortly after it has begun, which gives me an opportunity to catch it before it completes.

« Free Will »: Are we all equal?

In our own recent study (Caspar & Cleeremans, 2016), we addressed essentially the same question through completely different means: we asked whether there are individual differences in the timing between the onset of the brain motor preparation, the moment of the conscious intention, and the action itself. Our hypothesis was that people who exhibit a short time window between their conscious decision to act and their action itself may have less time to inhibit the upcoming action. We therefore correlated these differences in timing with personality variables, in particular the impulsivity trait.

We observed that the most impulsive individuals exhibited the shortest time window between the moment of their conscious intention to act and their keypress (see figure above). You can see that people who scored high on attentional and/or motor impulsivity were also those who reported the longest time window between the moment of their conscious intention (as indicated by more negative values) and the keypress. This suggests that individuals who score high on impulsivity have less time to inhibit their actions, and hence that global personality traits cast at the agent level influences both how the loopy sub-personal low-level neural processes that underpin behaviour unfold over time and the extent to which such processes are susceptible to be modified online.

This finding opens up many avenues for further research. May it be, for instance, that one can train oneself to become more sensitive to early signs of impending action and hence improve our ability to exert control over our own behaviour? Would similar findings obtain with other personality variables? More generally, our finding suggests that free will is not a given. Perhaps some of us — even if none of us could ever “do otherwise” — have more opportunities to exercise our freedom than others. As Dennett puts it, “Freedom evolves”…

Featured image credit: Underground. CC0 via Pixabay.