section_path: Scientific approaches/Neuroscience and neurophilosophy
section_name: Neuroscience and neurophilosophy
paragraph_text: Neuroscience and neurophilosophy
  
  It has become possible to study the living brain, and researchers can now watch the brain's decision-making process at work. A seminal experiment in this field was conducted by Benjamin Libet in the 1980s, in which he asked each subject to choose a random moment to flick their wrist while he measured the associated activity in their brain; in particular, the build-up of electrical signal called the readiness potential (after German Bereitschaftspotential, which was discovered by Kornhuber & Deecke in 1965.). Although it was well known that the readiness potential reliably preceded the physical action, Libet asked whether it could be recorded before the conscious intention to move. To determine when subjects felt the intention to move, he asked them to watch the second hand of a clock. After making a movement, the volunteer reported the time on the clock when they first felt the conscious intention to move; this became known as Libet's W time.
  
  Libet found that the unconscious brain activity of the readiness potential leading up to subjects' movements began approximately half a second before the subject was aware of a conscious intention to move.
  
  These studies of the timing between actions and the conscious decision bear upon the role of the brain in understanding free will. A subject's declaration of intention to move a finger appears after the brain has begun to implement the action, suggesting to some that unconsciously the brain has made the decision before the conscious mental act to do so. Some believe the implication is that free will was not involved in the decision and is an illusion. The first of these experiments reported the brain registered activity related to the move about 0.2 s before movement onset. However, these authors also found that awareness of action was anticipatory to activity in the muscle underlying the movement; the entire process resulting in action involves more steps than just the onset of brain activity. The bearing of these results upon notions of free will appears complex.
  
  Some argue that placing the question of free will in the context of motor control is too narrow. The objection is that the time scales involved in motor control are very short, and motor control involves a great deal of unconscious action, with much physical movement entirely unconscious. On that basis "...free will cannot be squeezed into time frames of 150–350 ms; free will is a longer term phenomenon" and free will is a higher level activity that "cannot be captured in a description of neural activity or of muscle activation..." The bearing of timing experiments upon free will is still under discussion.
  
  More studies have since been conducted, including some that try to:
  
  Benjamin Libet's results are quoted in favor of epiphenomenalism, but he believes subjects still have a "conscious veto", since the readiness potential does not invariably lead to an action. In Freedom Evolves, Daniel Dennett argues that a no-free-will conclusion is based on dubious assumptions about the location of consciousness, as well as questioning the accuracy and interpretation of Libet's results. Kornhuber and Deecke underlined that absence of conscious will during the early Bereitschaftspotential (termed BP1) is not a proof of the non-existence of free will, as also unconscious agendas may be free and non-deterministic. According to their suggestion, man has relative freedom, i.e. freedom in degrees, that can be increased or decreased through deliberate choices that involve both conscious and unconscious (panencephalic) processes.
  
  Others have argued that data such as the Bereitschaftspotential undermine epiphenomenalism for the same reason, that such experiments rely on a subject reporting the point in time at which a conscious experience occurs, thus relying on the subject to be able to consciously perform an action. That ability would seem to be at odds with early epiphenomenalism, which according to Huxley is the broad claim that consciousness is "completely without any power... as the steam-whistle which accompanies the work of a locomotive engine is without influence upon its machinery".
  
  Adrian G. Guggisberg and Annaïs Mottaz have also challenged those findings.
  
  A study by Aaron Schurger and colleagues published in the Proceedings of the National Academy of Sciences challenged assumptions about the causal nature of the readiness potential itself (and the "pre-movement buildup" of neural activity in general), casting doubt on conclusions drawn from studies such as Libet's and Fried's.
  
  A study that compared deliberate and arbitrary decisions, found that the early signs of decision are absent for the deliberate ones.
  
  It has been shown that in several brain-related conditions, individuals cannot entirely control their own actions, though the existence of such conditions does not directly refute the existence of free will. Neuroscientific studies are valuable tools in developing models of how humans experience free will.
  
  For example, people with Tourette syndrome and related tic disorders make involuntary movements and utterances (called tics) despite the fact that they would prefer not to do so when it is socially inappropriate. Tics are described as semi-voluntary or unvoluntary, because they are not strictly involuntary: they may be experienced as a voluntary response to an unwanted, premonitory urge. Tics are experienced as irresistible and must eventually be expressed. People with Tourette syndrome are sometimes able to suppress their tics for limited periods, but doing so often results in an explosion of tics afterward. The control exerted (from seconds to hours at a time) may merely postpone and exacerbate the ultimate expression of the tic.
  
  In alien hand syndrome, the affected individual's limb will produce unintentional movements without the will of the person. The affected limb effectively demonstrates 'a will of its own.' The sense of agency does not emerge in conjunction with the overt appearance of the purposeful act even though the sense of ownership in relationship to the body part is maintained. This phenomenon corresponds with an impairment in the premotor mechanism manifested temporally by the appearance of the readiness potential recordable on the scalp several hundred milliseconds before the overt appearance of a spontaneous willed movement. Using functional magnetic resonance imaging with specialized multivariate analyses to study the temporal dimension in the activation of the cortical network associated with voluntary movement in human subjects, an anterior-to-posterior sequential activation process beginning in the supplementary motor area on the medial surface of the frontal lobe and progressing to the primary motor cortex and then to parietal cortex has been observed. The sense of agency thus appears to normally emerge in conjunction with this orderly sequential network activation incorporating premotor association cortices together with primary motor cortex. In particular, the supplementary motor complex on the medial surface of the frontal lobe appears to activate prior to primary motor cortex presumably in associated with a preparatory pre-movement process. In a recent study using functional magnetic resonance imaging, alien movements were characterized by a relatively isolated activation of the primary motor cortex contralateral to the alien hand, while voluntary movements of the same body part included the natural activation of motor association cortex associated with the premotor process. The clinical definition requires "feeling that one limb is foreign or has a will of its own, together with observable involuntary motor activity" (emphasis in original). This syndrome is often a result of damage to the corpus callosum, either when it is severed to treat intractable epilepsy or due to a stroke. The standard neurological explanation is that the felt will reported by the speaking left hemisphere does not correspond with the actions performed by the non-speaking right hemisphere, thus suggesting that the two hemispheres may have independent senses of will.
  
  In addition, one of the most important ("first rank") diagnostic symptoms of schizophrenia is the patient's delusion of being controlled by an external force. People with schizophrenia will sometimes report that, although they are acting in the world, they do not recall initiating the particular actions they performed. This is sometimes likened to being a robot controlled by someone else. Although the neural mechanisms of schizophrenia are not yet clear, one influential hypothesis is that there is a breakdown in brain systems that compare motor commands with the feedback received from the body (known as proprioception), leading to attendant hallucinations and delusions of control.