Grey Matters: Does Alien Hand Syndrome Refute Free Will?



Neuroscience opens many fascinating windows into human nature. In the quest to understand human consciousness, volition, and intentionality, there is much to learn from studying even the brain’s flaws and failures.

Imagine that it were possible to drive a philosophical wedge between the carrying out of a purposeful act and the recognition of that act as one’s own. Would the severing of act from ownership abolish the belief that humans possess free will?

Consideration of an unusual brain lesion shifts that question from the hypothetical to the practical. We recently reported the case of a woman who was startled at dinner when her left hand suddenly began to interfere with her efforts to eat. Each time she brought food to her mouth, her left hand reached up and struggled with her right hand, groped about her face, and even struck her in the cheek. It seemed that her left hand had acquired a mind of its own. This bizarre behavior was explained by an acute stroke in her right parietal lobe visualized by magnetic resonance imaging (MRI).[1] The stroke damaged the connection between the part of the motor cortex that moved the left hand and the parietal cortex that perceived the left hand movements as her own. She had lost the sense of ownership of the hand’s behavior. Over time she regained conscious control of her hand but did not fully recover proprioception. Because she could not discern the position of her left hand, the hand continued to make occasional automatic exploratory movements, termed pseudoathetosis, to gain a sense of spatial orientation.

The term “alien hand syndrome” refers to a variety of rare neurological conditions in which one extremity, most commonly the left hand, is perceived as not belonging to the person or as having a will of its own, together with observable uncontrollable behavior independent of conscious control. Alien hand syndrome has been described in patients with lesions of the frontal or parietal lobes or their interconnections, especially in the corpus callosum, which joins the left and right cerebral hemispheres, as well as in certain neurodegenerative diseases such as corticobasal degeneration.

The apparently purposeful movements of the alien hand are goal-directed, which distinguishes them from the involuntary spasms of simple reflexes such as chorea or myoclonus. Some patients exhibit intermanual conflict, in which the movements of the left hand oppose the actions executed by the right hand, without necessarily performing the opposite action. For example, one patient put on clothes with the right hand only to pull them off with the left hand.[2] The hands of another patient struggled with each other as they competed to answer the telephone.[3] Another patient tried to turn left while driving, at which point the other hand tried to turn the steering wheel to the right.[4] Other patients have exhibited grasping and groping behaviors or compulsive manipulation of tools, opening or taking off eyeglasses, folding the frame, and putting them away, for example.[5] While playing checkers, another patient’s left hand made a move he did not wish to make. He corrected the move with the right hand, and to his frustration, the left hand responded by repeating the false move.[6] These uncontrollable behaviors can be quite distressing to the patient.

Some psychologists have cited the alien hand syndrome as evidence in support of the philosophical position that human free will does not exist. Daniel Wegner, for example, in arguing that all conscious will is an illusion, considers the alien hand syndrome to be an example of the undermining of the experience of volition. The gestures of the alien hand are, in his view, fatal to the idea of mental agency. “The fact is,” writes Wegner, “we find it enormously seductive to think of ourselves as having minds, and so we are drawn into an intuitive appreciation of our own conscious will.”[7] The absence of awareness of having willed the alien hand to act, such that the patient feels a remote spectator to the actions of the hand which seems to have a mind of its own, leads psychiatrist Raj Persaud also to embrace a deterministic view of human nature. Since the brain is the seat of all our experiences, he argues, then there is “a part of our nervous system which is responsible for our belief that we have free will over our behavior.”[8] “The delusion that we are responsible for all our actions,” Persaud concludes, is “one of the prices we had to pay for conscious awareness of ourselves to evolve as a function of the brain.”[9]

Whether one is free to disagree with a deterministic view of human nature is a question on which the very possibility of ethics depends. For if free will is ultimately a delusion and human decisions are reducible to the blind product of material efficient causes, then there could be no reason to argue that one ought to choose to act in a certain way instead of another. Nor would personal decision and moral responsibility be anything more than companion illusions. It would make no sense to appeal to reason as a guide to decisions if all thought ultimately reduces to the irresistible consequence of material causes prodding us as inexorably as lines of computer code.

The evidence, however, has not proved the case for determinism but remains open to various philosophical interpretations, including those that accommodate a view of human nature grounded in free will. Empirical proof of determinism would require a description of the sum of causes leading to a decision alleged to be fully determined. Wegner concedes, however, that, “We can’t possibly know (let alone keep track of) the tremendous number of mechanical influences on our behavior because we inhabit an extraordinarily complex machine.”[10] So the claim that all decisions are the product solely of material influences, including those inaccessible to investigation or that have not been demonstrated or measured, is a philosophical conjecture that lacks the scientific status of an empirically verified statement.

There is also the problem of how well a mechanistically determined brain could understand itself. If knowledge were attainable only through the material workings of a brain lacking the capacity to reason freely, one could not be certain whether a theory of human action corresponded to reality rather than just reflecting the way the brain happens to be organized.

It is, of course, not surprising to find that there would be an area of the brain possessing knowledge of personal agency if free will truly exists. Loss of the knowledge that one has acted freely, for example, in the case of the patient with a lesion in the right parietal lobe, leads more directly to a diagnosis of the brain’s condition than to a sweeping statement about the nature of reality and free will. The acquired inability to perceive alien hand behavior as volitional may represent a form of agnosia, which means loss of the ability to recognize some aspect of reality despite receiving the specific sensory information. Consider, as an analogy, the patient with a right temporal lobe lesion who, though able to hear, loses the ability to recognize the rhythm and harmony of sounds or experience notes as musical. This agnosia for music is known as receptive amusia.[11] One would be mistaken to conclude that the once heard but now misapprehended Mozart symphony had been an illusion. Unlike the symphony, which other observers could verify as real, conscious free will is subjectively and personally discerned. Agnosia for free will would mean the loss of the sense of agency that normally arises when one freely and purposively acts. In the case of alien hand syndrome, agnosia for free will is limited to particular behaviors of the nondominant hand.

Proponents of determinism might also point out that the alien hand syndrome is proof in principle that the brain has the capacity to generate purposeful actions apart from intentional decision or even conscious awareness and that free will must, therefore, be unnecessary to explain human behavior. It is unclear, however, whether all goal-directed behaviors belong to the same category as alien hand behavior. There would seem to be an important difference between the almost automatic yet complex routine motion of, for example, bringing a cup to one’s mouth and the highly intentional, thoughtful and creative act of writing a letter to a family member. The latter could not be done by the most skillful alien hand under the direction of a disconnected motor cortex. To acknowledge that alien hand action is not freely willed would not be to conclude that all nontrivial human action is determined. The findings of functional MRI support such a distinction. In a patient with a right parietal stroke, alien left hand movements correlated with isolated activation by intentional planning systems of the right primary motor cortex, presumably released from conscious control. Voluntary hand movements, by contrast, activated a distributed network involving not only the primary motor cortex but also premotor areas in the inferior frontal gyrus.[12]

Another way to interpret the purposeful yet apparently unintentional behavior of the alien hand would be to suppose that it results from a fragmentary expression of free will. Alien hand movements might be freely generated yet incompletely purposeful, being isolated from other brain regions normally supplying the contextual features of intentional behavior. Released from inhibition by normally restraining subconscious neural influences, such movements would not incur moral responsibility. Cut off from the neural pathways that compose the signature of conscious awareness, the intrusive behaviors of the wayward left hand would go unrecognized as one’s own.

As neuroscience probes more deeply into the nature of human thought and behavior, much has been elucidated, and much more awaits discovery. Some of the remaining questions may seem unsettling at first. One such question is how the exercise of free agency might at times occur independently of full conscious awareness. Another is how various unseen external and internal factors influence our choices and habits. In these matters, neuroscience suggests that we are not as free and in control of our actions as we might like to think. Nevertheless, the curious gestures of the alien hand and their ostensibly materialistic philosophical implications have not rendered free will obsolete. The neural traces of freedom, though subtle, are wonderfully consequential.

Our inner thoughts are no doubt more complex than brief self-examination can discern and more conflicted than we might prefer to admit. Discerning the inner turbulence common to all who wrestle with matters of conscience, the apostle Paul wrote, “For I do not understand my own actions. For I do not do what I want, but I do the very thing I hate.”[13] In this respect, the alien hand syndrome may be an accurate metaphorical portrait of the universal moral condition of humankind, in need, often unknowingly, of the Great Physician to grant us the undivided heart that the prophets of old so earnestly sought.[14]



[1] Spector AR, Freeman WD, Cheshire WP. “The Stroke that Struck Back: An Unusual Alien Hand Presentation.” Journal of Stroke & Cerebrovascular Diseases 2009; 18(1): 72–73.

[2] Aboitiz F, Carrasco X, Schröter C, et al. “The Alien Hand Syndrome: Classification of Forms Reported and Discussion of a New Condition.”Neurological Sciences 2003; 24: 252–257.

[3] Doody RS, Jankovic J. “The Alien Hand and Related Signs.” Journal of Neurology, Neurosurgery, and Psychiatry 1992; 55: 806–810.

[4] Ibid.

[5] Ibid.

[6] Wegner DM. The Illusion of Conscious Will. Cambridge, MA: Massachusetts Institute of Technology Press, 2002, pp. 3-6, 26–28.

[7] Ibid.

[8] Persaud R. “Sensory Alien Hand Syndrome.” Journal of Neurology, Neurosurgery, and Psychiatry 1999: 67: 130–131.

[9] Ibid.

[10] Ibid.

[11] Berman IW. “Musical Functioning, Speech Lateralization and the Amusias.” South African Medical Journal 1981; 59: 78–81.

[12] Assal F, Schwartz S, Vuilleumier P. “Moving With or Without Will: Functional Neural Correlates of Alien Hand Syndrome.” Annals of Neurology2007; 62(3): 301–306.

[13] Romans 7:15, ESV.

[14] Ezekiel 11:18, Psalm 86:11.


Editor’s Note: The views expressed herein are Dr. Cheshire’s own and do not necessarily reflect the position of Mayo Clinic or Mayo Foundation, USA. This article originally appeared in Ethics & Medicine: An International Journal of Bioethics 26, no. 2, (2010) and is used with permission.


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