Scientists at the RIKEN Center for Life Science
Technologies, along with researchers from the AIST
Human Technology Research Institute in Japan, have
identified a time-dependent interplay between two
brain regions that contributes to the recovery of
motor function after focal brain damage, such as a
stroke.
Performance on the precision-grip task - Two days after lesion, monkeys perform poorly compared to before the injury. Twenty-nine days after injury performance was greatly improved and resembled that from before injury.
Published in the Journal of Neuroscience, the
research shows that when motor functions are
remapped through rehabilitative training, brain
regions relatively distant from a lesion are
recruited during the initial stages and functional
connections with regions near the lesion are
strengthened during the latter stages.
The research team investigated the special kind of
neural plasticity that allows the recovery of motor
function after brain damage, focusing on changes
that occur during the course of rehabilitative
training. This kind of training is known to promote
structural and functional alterations in the brain
that improve impaired motor ability, but how it does
so is a question that neuroscientists are still
trying to answer.
The team studied the rehabilitation process in
monkeys that had suffered injury to the region of
the cerebral cortex that controls hand movements.
This region of the primary motor cortex is
especially needed for fine movements, such as those
required to grip and manipulate small objects using
fingers. To facilitate recovery of motor function,
the researchers taught monkeys to quickly and
repeatedly grab a piece of potato through a small
opening using their thumbs and index fingers—a task
that requires a high degree of manual dexterity.
Brain regions and mechanisms involved in motor-function recovery - (Left) Activity in the ventral premotor cortex was higher during the early stage of recovery. Note that this region is somewhat far from the lesion. (Right) Functional connections between the lesion site and regions of primary motor cortex immediately surrounding it became stronger in the later stages of recovery. The blue arrow points to the lesion site.
LAs expected, the team found that performing this
task 30 minutes a day for several weeks after injury
resulted in greatly improved motor function. To
estimate changes in brain activity associated with
the recovery, they imaged the regional brain
activity using H215O-positron emission tomography (PET)
before injury and at the early and late stages of
recovery while monkeys performed the task. They
found that activity in the ventral premotor cortex—a
brain region somewhat distant from the injury—was
higher during the early stage of recovery than
before the injury. They also conducted what is known
as a psychophysiological interactions (PPI) analysis
and found that when monkeys performed the task in
the later stages of recovery, connections between
the lesion site and regions of primary motor cortex
immediately surrounding it became stronger.
To verify whether the changes in these regions were
in fact necessary for the recovery, they temporarily
inactivated them before injury and at the recovery
stages. They found that inactivation of the ventral
premotor region on the same side of the brain as the
lesion impaired precision grip during the early
stages of recovery—even when it was limited to
regions that had not been essential to hand
movements before the injury. They also found that
the area surrounding the injury became devoted to
movements related to precision grip. During the
later stage of recovery, inactivating this area only
affected precision grips, but not other types of
grips that had been impaired by inactivation before
the lesion.
When explaining their excitement for these new
findings, Yumi Murata from AIST noted that, “they
will likely contribute to the development of new
rehabilitation techniques and drugs, as well as new
ways to evaluate rehabilitative training.” Hirotaka
Onoe from RIKEN added that “new rehabilitation
techniques will help reduce the burden that these
types of strokes have on the patients and their
families.”
For more information
Murata et al. (2014)
Temporal Plasticity Involved in Recovery from Manual
Dexterity Deficit after Motor Cortex Lesion in
Macaque Monkeys. J. Neurosci.
doi:10.1523/jneurosci.1737-14.2014
RIKEN.
MDN |