快猫短视频

PEOPLE who have lost a limb often experience chronic pain seemingly coming
from the missing limb, or feel sensation in the absent limb if someone touches
their face. Following a study using monkeys, researchers say this is caused by a
deep-seated rewiring of the brain.

Conscious thought and memory are dealt with in the cortex. When part of the
cortex no longer receives sensory input鈥攂ecause of amputation or a spinal
cord injury鈥攁djacent nerves encroach on the defunct region, essentially
taking it over. This often results in people perceiving a missing limb, or
suffering constant pain.

Neuroscientists suspected that this migration might be triggered by changes
in more primitive areas of the brain, such as the brainstem, which handles
automatic and instinctive functions. One clue was the frequent link between
touching the face and feeling sensation in a missing arm. Nerves from the arm
enter the brainstem at a point called the cuneate nucleus, while facial nerves
culminate right next door at the trigeminal nucleus.

No studies have yet shown communication between neighbouring nuclei in the
brainstem in people. But a team of researchers at Vanderbilt University in
Nashville, Tennessee, has now shown that growth can cross boundaries between
nuclei in the brainstem of adult monkeys who have had the nerves to their arms
cut, or have had an arm amputated for medical reasons. The monkeys sprouted
connections from the trigeminal into the cuneate nucleus. 鈥淎lthough some believe
that there are pre-existing connections in the cortex, there are no known
connections between the hand and face nuclei in healthy primates at the
brainstem level,鈥� says team member Neeraj Jain.

鈥淭he amount of sprouting shown here is quite substantial, so it needs to be
taken seriously,鈥� says Edward Jones, Director of the Center for Neuroscience at
the University of California at Davis. 鈥淏ut this doesn鈥檛 tell us the exact
mechanism yet. Once you start exploring these phenomena from a molecular level,
only then is there the opportunity to intervene.鈥�

Up in the cortex, the area that receives input from the arm and hand is again
next to that of the face. This leads Jain and his colleagues to suggest that
changes in the brainstem and the cortex may be connected. 鈥淲e already know that
the brain is very plastic,鈥� says Jain. 鈥淏ut now we have a handle to actually
tackle this problem.鈥�