The brain maintains an unchanged representation of one hand even after it has been removed: an important information for neuroprostetics.
A study that observed how the brain “map” the position of the limbs in space could improve the treatment of phantom limb pain, coming from a part of the body that has been amputated. The search for the universities of Cambridge (United Kingdom) and Pittsburgh (Pennsylvania), published on Nature Neuroscienceit is the first to have followed three people even before a programmed amputation of the hand, and not only to the intervention that took place.
A map of the body in the brain
The different parts of the human body are represented in the primary somatosensory cortex, an external and recent layer of the brain located in the parietal lobe (under the upper part of the head) and in charge of receiving sensory stimuli. This representation, disproportionate for some parts of the body capable of refined movements such as hands, feet and mouth, serves to map sensory stimuli such as those relating to touch, temperature, pain and position in space.
It was a hypothesis shared between the neuroscientists, which following the amputation of an limb the cerebral regions close to that corresponding to the amputated part, through the phenomenon of neuroplasticity, reorganized to “recycle” the area corresponding to the missing limb and overwrite its function: in essence, to reuse the neurons first used for the perception of the limb thus the use of the resources remained.
Yet it was there!
However, the fact that most of the amputated people report sensations of pain or itching at the headquarters of the missing limb (ghost limb syndrome) It seems to indicate that the brain retains a spatial memory of that missing body portion. To give further weight to this second hypothesis, British and US scientists for the first time studied the maps on the primary somatosensory cortex of hands and face in three people who had to meet a programmed amputation of one hand for various medical reasons.
As if nothing had happened
The researchers asked the participants to move the individual fingers of the hand destined for intervention and to curl their lips while observing their brain with functional magnetic resonance imaging (FMRI), which measures brain activity by monitoring changes in blood flow. They reconstructed the map of hands and lips on the cortex and repeated the operation – asking, this time, to imagine to move the missing fingers – after three, six, eighteen months and after five years from the amputation.
Even after the intervention, the same identical areas that once controlled the missing limbs, as if the cortex had not recorded the amputation, were activated in the brain of the participants. The regions corresponding to the lips, neighboring in the cortex to those of the fingers, had not expanded or expanded on those nearby orphans of the limb.
Therapeutic repercussions
The discovery could be useful in the treatment of the pain of the ghost limb or improve brain-computer interface technologies: “Now these technologies can operate starting from the assumption that the Body Map of the brain remains constant over time” explains Hunter Schone, among the authors of the study. “This allows us to advance towards the next frontier: to access the finer details of the hand map, how to distinguish the tip of the finger from the base, and restore the rich qualitative aspects of the sensation, such as consistency, shape and temperature”.
