Neurology of widely embedded free will.

Free will is classically attributed to the prefrontal cortex. In clinical neurology, prefrontal lesions have consistently been shown to cause impairment of internally driven action and increased reflex-like behaviour. Recently, parietal contributions to both free selection at early stages of sensorimotor transformations and perception of specifically self-intended movements were demonstrated in the healthy brain. Such findings generated the concept that 'free will' is not a function restricted to the prefrontal cortex but is more widely embedded in the brain, indeed including the parietal cortex. In this paper, a systematic re-interpretation of parietal symptoms, such as apraxia and reduced sense of agency, is given with reference to the consequences of reduced freedom of selection at early stages of sensorimotor transformation. Failed selection between possible movement options is argued to represent an intrinsic characteristic of apraxia. Paradoxical response facilitation supports this view. Perception of self-intended movement corresponds with a sense of agency. Impaired parietal distinction between predicted and perceived movement sensations may thus equal a restricted repertoire for selection between possible movement options of which intention is attributed to either oneself, others or an alien hand. Sense of agency, and thus perception of free will, logically fits a model of the parietal cortex as a neuronal interface between the internal drive to reach a goal and a body scheme required to select possible effectors for motor preparation.