On the Dynamic and Ever Changing Brain

brain sites stimulated and measured; from Ref. 1

It is well accepted that the activity in our brains is not simply defined by the anatomical connectivity therein. However, one of the great mysteries of free will (if it actually does exist) is how a conscious state (the current pattern of electrical activity) is causally linked to subsequent states (the next pattern of activity). If it is truly deterministic, then free will may truly be an illusion.

A recent paper reporting results from an experiment in which awake human cortices were stimulated and responses measured, makes an implicit comment on these matters. In this experiment, patients going in for brain surgery volunteered to have their cerebral cortices experimented on. This is not as invasive as it sounds since the experiment involved only a reanalysis of data obtained from necessary pre-surgical procedures. The experimental paradigm consisted of simply electrically stimulating the cortex at various points and measuring the evoked activity at other sites. The authors were curious how regular these responses would be, and how they would vary over time.

They found that "The likelihood of an afterdischarge at an individual site after stimulation was predicted by spontaneous electroencephalographic activity at that specific site just prior to stimulation, but not by overall cortical activity" (ref. 1). The intriguing part about this is that the overall activity does not predict the subsequent activity, supporting the notion that there is something else (free will?) that intervenes or contributes to the causation involved in moving to another state of activity. However, it must be noted that the overall activity might not be predictive for another reason. Aggregate brain activity is made up of parts devoted to distinct cognitive functions. Thus if the brain area stimulated was one devoted to motor function and the subject happened to be thinking about a movie prior to stimulation, the activity devoted to the visual experience wouldn't necessarily be predictive of how the activity might spread through the brain from this motor area. Nonetheless, it may be the case that this sort of variation - the seemingly random, highly dynamic snatches of activity present in the brain at any given moment - contribute to our sense of free will, and the rich landscape of experience that we go through.

References:
1. Lesser RP, Lee HW, Webber WR, Prince B, Crone NE, Miglioretti DL. (2008) Short-term variations in response distribution to cortical stimulation. Brain, 131 :1528-1539