Wednesday, 8 April 2009

Mostly Armless

A regular reader and personal friend, Petra, put me on to this little story. One that I'd missed.

From Science Daily :
Phantom limbs, often described after amputation, are also experienced as an extra limb in patients who are paralyzed on one side following a stroke. Referred to as supernumerary phantom limb (SPL), patients can usually perceive these limbs as a vivid somatosensory presence of an extra limb, but generally cannot see or intentionally move them. In some unusual cases, however, patients have reported seeing their phantom limb or feeling objects or body parts with it, which indicates that multiple areas of the brain may be involved in SPLs.

A new study on a patient who experienced an SPL which she could feel, see and intentionally move is published in Annals of Neurology, the official journal of the American Neurological Association and the Child Neurology Society. It is one of the very few studies to investigate brain activity connected to SPLs.

The study involved a 64-year-old woman who suffered a stroke and was subsequently paralyzed on her left side. A few days after the stroke, she experienced an SPL starting from the elbow of her paralyzed left arm, which she described as “pale,” “milk-white” and “transparent.” She claimed she could move, see and even use the SPL to touch parts of her body such as her head and right shoulder, but that she experienced it only when she decided to “trigger” it intentionally. She even claimed to be able to use it to scratch an itch on her head, with an actual sense of relief. She also reported that the phantom limb could not penetrate solid objects
So far, nothing much new. Except there's this, which has come out of Left Field...
Led by Asaid Khateb of Geneva University Hospitals, researchers conducted functional magnetic resonance imaging scans to analyze the patient’s brain activity during actual and imagined movements of her healthy right hand, imagined movements of her paralyzed left hand and movements of the SPL.

The real movements of the right hand were associated the dominant activation of left areas of the brain associated with movement, perception of stimuli and visual processing, as expected. Similar but less extensive activations were seen with imaginary movements of the right hand. In contrast, imaginary movements of the paralyzed left hand showed dominant activation in areas associated with movement in right side of the brain. When asked to scratch her cheek with the SPL, areas of the brain associated with movement and vision were activated, which confirmed her report that she could see and move her SPL. In addition, a measurable sensory response was also detected when she scratched her left cheek with the SPL.
Who ordered THAT?? We can come up with some plausible explanations for brain activity in the motor section, either in the paralysed arm or the "new" one that's just been acquired. Clues as to how body image is mapped in the brain, something we have only the barest understanding of at the moment.

But when the imaginary arm scratches an itch, there's a measurable sensory response. We can't say the response is a figment of the imagination, something purely psychological. Not only does the patient say it's real, so does the MRI scan, objective rather than subjective evidence.

I'm not even going to try to formulate a conjecture on this one.

More at, but as that was published on April 1st, there was a certain credibility problem.

When I first read this, I was immediately reminded of some stories by Larry Niven. Ones involving Gil "the Arm" Hamilton. Life imitating Art?

Anyway, another part of the puzzle. One that can't be wished away simply because it's inconvenient.


Battybattybats said...

Sounds like the old fashioned notions of psychosomatic response when they were used to explain some of the phenomena observed in mesmerism and hypnosis experiments.

It might be interesting to see what MRI scans of people in guided trance states experience.

Guess that cartesian dualism may be headed for it's final end.

timberwraith said...

Oh my goodness, I thought of the Gil Hamilton stories too!