Bridging Brain, Mind, and Behavior
Research Award
James S. McDonnell Foundation
Brain Plasticity and Neuro-Rehabilitation
Our brains are constantly changing throughout our
lives. Connections between neurons are
strengthened or weakened as we learn each new skill and acquire each new
memory. Such circuitry changes, called ‘brain
plasticity’, serve to optimize the brain’s function to meet each
individual’s needs. If I decide
one day I want to get better at tap dancing, wine tasting, or identifying bird
calls, my brain is happy to oblige and rewire its circuits to make these skills
possible. Practice makes perfect because
practice triggers plasticity.
The observation that people can get ten times better
at most simple tasks with a few weeks of practice has lead some to wrongly
conclude that we use only ten percent of our brains. In fact, the brain allocates its computational
resources with great efficiency. Brain
plasticity allows neural networks to accomplish difficult tasks that evolution
never selected for, including freeway driving, Braille reading, and
calculus. The nervous system, like the
immune system, evolved to solve undefined problems and adapt to changing
environments. Even the brain’s
remarkable ability to adapt does have limits, however.
Brain damage can cause pain, paralysis, blindness,
and loss of language depending on the regions of the brain that are
affected. Plasticity helps restore some
function by rewiring damaged circuits, but is often insufficient for full
recovery, even after months of rehabilitation.
Despite advances in neurosurgery, there is presently
no way to directly rewire the brain.
While physicians can treat many of the symptoms of brain damage, there
is little they can do to stimulate recovery.
In this way treatment for neurological disease is very much like
treatment for infection and cancer was a century ago. Recent research offers new hope for millions of
stroke patients struggling to regain lost independence. It may one day be possible to rebuild
damaged circuits and restore lost function by guiding plasticity in much the
same way that doctors now routinely manipulate the immune system.
We know from studies of normal learning that
plasticity depends on repetition and attention.
If I intently practice bird call identification, for example, the part
of my brain that responds to these sounds would increase, making it easier to
distinguish the subtle differences between them. However, if I simply heard the sounds over
and over without focusing on them, there would be no change in my brain and I
would learn nothing. Focused attention
stimulates release of neurotransmitters that encourage plasticity and
learning. Without this mechanism to
regulate plasticity our neurons would try to learn every detail about common,
but useless stimuli like air conditioner sounds and the textures of our
clothes.
During the period after brain damage decreases
levels of neurotransmitters like acetylcholine, dopamine, and norepinephrine are decreased, limiting the brain’s
rewiring potential. Drugs that increase
release of these transmitters don’t help much because they tend to
stimulate non-specific plasticity.
However, if one could direct the form of plasticity stimulated by these
drugs, it might be possible to control rewiring and restore lost function.
I have recently demonstrated that it is possible to
precisely manipulate plasticity in animals by controlling neurotransmitter
release and sensory experience. Using
electrical stimulation of one of the brain’s learning centers,
I was able to alter both the brain’s wiring and processing speed. My next goals are to develop a method to
control plasticity by combining drug therapy with sensory stimulation and to
test its effectiveness in restoring functions lost to brain damage.
Preliminary evidence indicates that combining speech
and physical therapy with pharmacological stimulation can significantly improve
recovery from stroke. As these
techniques are refined, they may make complete recovery from stroke a realistic
goal. The potential to manipulate
plasticity in humans would also be beneficial for patients suffering from other
neurological disorders. Many scientists
believe that epilepsy, focal dystonia, tinnitus, and
chronic pain result from pathological forms of plasticity. While current treatments attempt to alleviate
the symptoms of these conditions, neurorehabilitation
could be used to reverse the bad wiring that causes them. It may even be possible to use therapeutic
plasticity as a treatment for psychiatric disorders, such as posttraumatic
stress disorder, drug addiction, obsessive-compulsive disorder, and phobia.
The proposed experiments will provide a solid
experimental foundation for further development of neurorehabilitation
to minimize side effects and optimize patient recovery. Although far from proven, neurorehabilitation
has the potential to transform the treatment of brain disease in the same way
that antibiotics and chemotherapy have changed the treatment of infection and
cancer.
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For preliminary findings see our Society for
Neuroscience 2005 Poster
