Third Hand: Useless But Interesting

I think this happened after the last concussion, but I’m not sure.   Not much more than five years, certainly not ten,  I think; I haven’t always had a third invisible hand and partial arm hanging on the wrong side of my body.  It started while I was distracted.   I gradually I became aware that one hand was uncomfortable (not painful, just “tight”–with a prickly sensation over the palm, as if holding something a little rough-textured a little too long.)  I’d been absorbed in what I was doing, and now the hand near my right thigh was calling attention to itself.  I glanced down…at nothing.  No hand there.   Looked again: both hands were in plain view, sort of in front of me.  (I don’t remember what I was doing the first time the third hand announced itself. ) The invisible hand that had intruded on my awareness felt like my hand–and very specifically my left hand–but why was I feeling it at all?

I knew about the phantom limbs that amputations cause…the limb your brain is used to monitoring isn’t there, but the software and hardware to monitor it still is in your brain…so your brain says “It’s there, and by the way it’s hurting.”  I had read Oliver Sacks’ account of his own experience after a very bad leg injury and surgery, where his leg didn’t feel like his–another common problem, this time with an attached but damaged body part.  As a neurologist he’d seen a lot of patients with similar experiences.  But an extra hand showing up in old age?  What caused that?  My real hands were there, and hadn’t suffered amputation or serious injury.  The thought that maybe my brain had suffered serious injury…that the various concussions had caused it…did not occur at once, because my conscious mind recoiled from that very scary thought before I could think it.  I’ve thought it since, of course, since the phenomenon has recurred again and again: I’ll suddenly notice that my left hand is holding something textured (up to prickly),  glance down at my leg, and check that the actual left hand is really still there.

It has a name: supernumerary extracorporeal phantom limb, often shortened to just “supernumerary phantom limb” or SPL.   Supernumerary because it’s a true extra–nothing’s missing.   It’s the phantom limb not resulting from amputation.  What does it result from?  In some cases, it results from a stroke (large or small) or a leaky aneurysm, or a brain tumor.  Traumatic brain injury can result in a supernumerary extracorporeal phantom limb, though it usually doesn’t.  Spinal cord injury (complete or incomplete) can cause it.  Severe injury to a limb, short of amputation, can cause it.   Apparently (if I understand the papers I’ve read about it) anything the disrupts the normal signaling cycle we use to determine where our body parts are…signals from tactile receptors going to the brain, and engaging the brain’s own concept of what “this-body” is, how it exists in space, and sending signals back directing movement and visual input…can result in the feeling that a limb is somewhere other than it “should” be, and thus experienced as an extra.  Though not everyone who has a TBI has been asked, “Hey, do you ever feel an extra hand or foot or nose?”  In other cases, it’s not known because the person with it hasn’t had one of the really modern brain-scans that can detect various anomalies.  Or because, like me, they just don’t tell a doctor of the type who might start digging to find out, or fear being labeled mentally ill and delusional.

Some people are very upset by the apparent presence of an invisible body part: some are frightened, some angry, some just don’t want it.  Treatment is generally intended not to fix it–make the sensation go away–but to make the patient more tolerant of having it.  There are some approaches (sort of physical therapy based) that have, sometimes, ended with the phantom vanishing.   Mine doesn’t really bother me.   Once I knew the range of sensations associated with it (a tingling like part of the body going numb from pressure on a nerve–as when a leg or foot has “gone to sleep” and is coming back to use) I could often identify its appearance without visually checking for it.  It doesn’t seem to be associated with any particular functional problem (clumsiness, balance difficulties, etc)  so it’s more like a curiosity on a display shelf.  Interesting, maybe a bit mysterious, but ultimately not a big deal at all.  Briefly, early on, I sortakinda hoped it would be useful, as in some science fiction or fantasy stories, something that could expand my ability to carry things, or catch things slipping off a stack of stuff I was already carrying.  It’s not.  It exists (mentally) where it is.   Recently, I’ve expended (for the heck of it) effort in trying to move its fingers a little…or seem to…and maybe I have.  But what the fingers are holding is as non-existent as the hand itself, so it makes no difference.   And since I was *trying* to feel that difference, it brings into question whether imagination, rather than actual neural feedback of some sort, was involved.  I have, after all, a lively, inventive, and active imagination (not a plot-making one, now, but thinking non-plot things up is still going on.)  Not worth pursuing, I decided.

It is tempting to put the origin of my third-hand experience at one of the two traumatic injuries just over four years ago–either the one in the fall of 2017, when the bike handlebar punched me in the neck, or the buck-off in February of 2018 that delivered the concussion that definitely did cause (it still causing me) problems.  But if “accumulation” of small injuries could lead to it, then I’d have to start much earlier, with the serious illnesses of childhood, the most serious of which was the encephalitis that caused partial deafness and residual weakness on the left side.  The deafness ended after a few years, but the left-sided weakness was obvious  for decades. By HS and early college, I had a spinal curvature from unequal muscle development; my mother adjusted the clothes she made me to fit a lopsided body.  I’ve had some neurological “things” going on for a long time.

So there it is.  A supernumerary left hand sometimes hovers around my upper right thigh, and accomplishes nothing but mildly intriguing me.