Dirk De Ridder, Sven Vanneste, Grant Gillett, Patrick Manning, Paul Glue, Berthold Langguth

A definition of free will is the ability to select for or against a course of action to fulfill a desire, without extrinsic or intrinsic constraints that compel the choice. Free will has been linked to the evolutionary development of flexible decision making. In order to develop flexibility in thoughts and behavioral responses, learning mechanisms have evolved as a modification of reflexive behavioral strategies. The ultimate goal of the brain is to reduce uncertainty inherently present in a changing environment. A way to reduce the uncertainty, which is encoded by the rostral anterior cingulate, is to make multiple predictions about the environment which are updated in parallel by sensory inputs. The prediction/behavioral strategy that fits the sensory input best is then selected, becomes the next percept/behavioral strategy, and is stored as a basis for future predictions. Acceptance of predictions (positive feedback) is mediated via the accumbens, and switching to other predictions by the dorsal anterior cingulate cortex (ACC) (negative feedback). Maintenance of a prediction is encoded by the pregenual ACC. Different cingulate territories are involved in rejection, acceptance and maintenance of predictions. Free will is known to be decreased in multiple psychopathologies, including obsessive compulsive disorder and addictions. In modern psychosurgery three target structures exist for obsessive compulsive disorder and addiction: the dorsal ACC, the nucleus accumbens, and/or the anterior limb of the internal capsula. Research in all three areas reports favorable results with acceptable side effects. Psychosurgical interventions seem to exert their effect by a common final common pathway mediated via the pregenual ACC. Successful neuromodulation increases the capacity to choose from different options for the affected individual, as well as inhibiting unwanted options, therefore increasing free will and free won't.