Phantom limbs are a well-known phenomenon where sensations and feelings are still experienced from a missing limb. In rare cases after brain injury, an additional phantom limb can appear – causing the sensation of a phantom third hand, arm or leg.
The drawings on the left are from two case studies of people with these ‘supernumerary phantom limbs’ recently published in the journal Neurology. They show an artist’s impression of the body sensations of two patients who suffered brain stem strokes.
Both patients had the experience of having a third arm and a third leg, although the male patients had the leg ‘appear’ along the midline of the body, while the female patient seemed to experience it ‘superimposed’ upon an existing leg.
One distressing element for the female patient was that although the patient could ‘move’ the phantom arm voluntarily, “she described occasional loss of control and feeling strangulated by the phantom arm around the neck”.
Two earlier case studies from neuropsychologist Peter Halligan and colleagues reported similarly disembodied extra limbs, but this time after damage to the right hemisphere of the brain.
As is more common after right hemisphere damage, these tended to have a delusional quality, so they weren’t just sensations – the patients genuinely believe their additional limbs existed.
One gentleman believed that he had a third arm in the middle of his body, and another believed that he had a third hand.
In this last case, the patient reported actually ‘seeing’ the additional limb, similar to this case study of a gentleman who believed he had a third leg protruding from his left knee after suffering a stroke that affected the thalamus:
He consistently maintained that the phantom leg was attached to his knee with a “bone plate” that “had no flesh on it”. However, he reported that the phantom limb itself looked normal and had a shinbone and a foot. It usually “appeared” in the morning when he was helped to put on his trousers. The patient stated that the phantom limb prevented him from turning over in bed, but did not adversely affect him otherwise.
When asked about how he knew about this leg he said that he could see it (despite his severe visual impairment) and feel it with his hand. He believed that the phantom limb belonged to him, although he readily accepted that it was not “normal” to have three legs. Initially he reported that the “leg” was growing from his own knee, but then reasoned that (given its size) he would have noticed it before the stroke.
At other times he believed the leg was attached to him by the nursing staff, but could not explain why. The patient was aware of phantom limb phenomena as his wife was an amputee. He was also aware that a stroke may affect perception and cognition. He did not believe either issue applied in his case.
The experience of a ‘supernumerary phantom limb’ is usually the result of a brain injury and typically resolves over time.
Phantom limbs are thought to arise because the somatosensory cortex, the part of the brain that represents the body’s sensations and feelings, reorganises so that the area previously used to represent the limb is partially ‘re-used’ for other functions, meaning the sensations sometimes get activated when these other functions are active.
Nevertheless, supernumerary phantom limbs are still mysterious, largely due to the small number of cases and diverse brain areas involved.
There is some suspicion that they might be caused because of disrupted communication between parietal lobes, which are known to represent body image, and the sensory feedback from the nerves in the body.
Link to abstract of Neurology case studies.
Link to full text of 1993 case study.
Link to full text of 1995 study.
Mind Hacks 
I have never heard of the phantom extra limbs before. The story of the guy with the perceived limb on his knee is fascinating!
Thanks for posting this!
Hi im in grade 9 in australia and i am doing a essa about this can you give me anymore detailed information?
Thanks 🙂
this caught my eye and didnt think it was something studied in any sort
Im 17 and have had the feelings of an extra pair of arms or possibly wings because of their size on my back… Ive had the feelling of them for quite some years now and are just like these other cases…. they will randomly burn and hurt, kill me practicaly because of the pain they give me… and i would have the feelling to move them and do things with them as to move or pick up objects…. and on certain nights or days (as i would usually get their feelling in the pm) i would have problems keeping my shirt on as i would feel the pressure of them trying to get out… which doesent work well with the fact that i am a girl and am claustrophobic 
i even have problems sometimes just trying to go to bed or laying on a couch 
i was wondering, what should i even do? i dont even have memory of a stroke of any kind…. a few concusions sure and being the type to scream all my thoughts in my head every day… but thats it 
I am 54;woman,married with 5 grown up kids.
Since a few months I feel a third arm, first I thought it was my left arm who felt sleepy, but no, with my left hand I was holding my cellphone close to my ear and the right hand lay just beside me… this third arm lay just in the middle on my leg.In the beginning I felt a bit amused, it did not hurt much,it was confusing..But now, after seeing a neurologist who thinks I am just fine and that this phenomen will dissapear like it appeared, suddenly. Because I told him it began to make me anxious, he prescribed me an RMI; but he even did not know how to formulate his demand on the paper, he never heard about such a thing before.I have an appointment on the first of october for the RMI.
Meanwhile it is getting worse, I can force that hand to open , close and it hurts more now, like a sleeping feet which you try to walk.More and more I feel a whole arm , starting somewhere from beside my neck on the left front side.It feels sometimes so heavy, tired, painfull that I try to grab instinctively that arm, but of course there is nothing. It appears during the day and also at night now, never in a specific situation.Sometimes for a few seconds and more often for several long minutes. The only other feeling that I have is often a headdick on the back of my head and also dizziness like I would faint.
Does someone felt the same or do you know what may be the cause of my third arm..?
Belgium, 15th of august 2015.
I have the same! A feeling of a third arm central from my chest. It clenches the hand and I feel the weight of it on my lap.I thought the worst, brain tumor but a scan showed nothing. My neurologist had never heard of any thing similar excepting of those who had lost a limb. It started in March and continues ?Dec 2018
My neurologist never heard of something like that neather but after a magnetic resonance (mri), he discovered that I had a small ischemic stroke… and that 4 other veins in my head were about to disrupt!!! So this third arm I felt was as a warning from my brain that something was really wrong! For about 6months he gave me a treatment against epilepsy, was hard to endure… But slightly my third arm vanished…
Now I must control my blood pressure and cholesterol. I take medecine for my blood to be more fluid, statines (medecine) against cholesterol.
Consider this signal as a warning from your brain… Be careful on your blood pressure, cholesterol level and ask for a MRI!!!
Wish you all the best!!!