I’ve just found a video of someone with alien hand syndrome – a condition which usually occurs after brain injury or stroke where the affected person loses conscious control over the hand and where it seems to move with a will of its own.
In this case, the video was uploaded by YouTube user frankenerin, who asked someone to video her when she was in intensive care after suffering a stroke and having brain surgery while her ‘alien hand’ was still present.
There’s a couple of things to notice in the video. The first is that the clinician asks the patient to do the actions for using scissors and brushing teeth. This is to check the problem is not a form of general ideomotor apraxia, where common action patterns are damaged.
She can do the actions with one hand but not the other, suggesting her strange movements are not due to global action planning problems.
The clinician then asks whether the patient recognises the arm as hers.
This may seem an odd question, but he’s checking for somatoparaphrenia, where patients can deny ownership of a paralysed or action-impaired limb, sometimes saying that it belongs to someone else.
As it turns out, the patient says she generally knows it is hers, but when it is draped across her body in a certain position and making involuntary movements she can think it is someone else’s limb. In other words, she seems to have fleeting somatoparaphrenia.
The video then shows the hand moving of its own accord and the patient having to use the other hand to keep it out of trouble.
Despite looking like she’s in pretty bad shape, frankenerin later posted a wonderful follow-up video where she is back on her feet and feeling fine, although discusses how she’s had to adjust her career aspirations owing to the longer-term effects of the brain injury.
Unfortunately, the Wikipedia page on alien hand syndrome, also known as anarchic hand syndrome, is dreadful, but there’s an excellent 2005 article from The Psychologist by neuropsychologist Sergio Della Sala that covers the neuropsychology of the condition and what it tells us about free will. You can read it online as a pdf.