There is a new paper in Neuron in which the authors have reprised a version of Libet’s famous experiments on volition, only the dependent measure is the activity of individual neurons in the medial frontal cortex. The recordings were obtained in the course of surgery for intractable epilepsy, and there will be much discussion of the details in the days and weeks to come, but some of the most salient observations come from the accompanying commentary by Patrick Haggard:
… the single-neuron data provide a reassuring confirmation of previous studies that recorded neural populations. A relatively small subset of medial frontal neurons showed a gradual ramp-like increase in firing rate before movement that recalls both EEG readiness potentials and recordings prior to memory-guided actions in trained monkeys. The time of conscious intention could be predicted from small subpopulations of these neurons, using an integrate-and-fire model, well before the time that participants reported the experience of volition. Of course, the time of conscious intention is closely linked to the time of action itself, so it is difficult to separate the relation between medial frontal activity and conscious intention from the relation between medial frontal activity and voluntary action.
The novelty of this study, however, lies in the fine grain of detail that it gives about the mechanisms of volitional action. This knowledge fills important gaps that are intrinsic to methods used previously: EEG recordings in humans lacked spatial precision, neuroimaging studies lacked fine temporal precision, and single-unit recording studies in animals lacked any conscious dimension.
This study will not put the remaining controversy over free will to rest, especially since it relies upon respondents to indicate when they made the decision to move their fingers, exactly as Libet did in his infamous experiments nearly 30 years ago. But the level of analysis is precisely the one that serious neuroscientists have always wanted, and the results are about as satisfying as one can imagine (and reinforce all of the existing concerns about what, exactly, fMRI reveals). Moreover, if there is any doubt that our brains can conjure up images of all sorts of ‘vital essences’ where there are none, I invite you to watch the video below of Theo Jansen’s Kinetic Sculpture. Brilliant.
Link to the paper in Neuron by Fried et al.
Link to the commentary by Haggerty
Hat Tip to James Fallows for the link to Theo Jansen’s sculpture.