Neuroplasticity and Reorganization of Brain Functioning, 2/1997


           The brain is constantly reorganizing structurally and functionally
           as it responds to stimuli and to injury. This ability to reorganize
           is referred to as "neuroplasticity". In very general terms, all
           areas of the brain adapt to a change in any one area of the brain
           because of the wealth of neurological connections to and from each
           area. Most of these changes are very subtle and do not usually
           result in dramatic changes in brain structure or function; however,
           significant alterations in behavior and/or performance can occur if
           the reorganization is either in a very specialized area of the brain
           or in a large volume of the brain.

           The period of most dramatic plasticity is during the first 2 years
           of life as the infant's brain becomes organized in response to its
           environment. At birth, most of the nerve circuits are in place
           anatomically but functional connections are awaiting stimuli.
           Plasticity is also challenged dramatically at any age when the brain
           responds to an injury (e.g.: a developmental injury; head trauma;
           stroke; a convulsion). The scientific issues are: what are the
           several mechanisms underlying neuroplasticity and what are the
           results on brain function of each of these several mechanisms,
           individually and collectively?

           On December 3-4, 1996, the National Institute of Neurological
           Disorders and Stroke of the National Institutes of Health conducted
           a research workshop exploring these issues. Basic and clinical
           research scientists from around the world met together and shared
           their research findings. Our Foundation participated in these
           discussions. The topic addressed was: what brain mechanisms underlie
           changes in performance following brain injury? Four mechanisms were
           discussed:

             Compensatory Masquerade: This mechanism involves "learning," the
             result of which permits one body part to compensate for loss of
             function in another body part. It is the basis of many clinical
             approaches used in rehabilitation and in orthopedic surgery. The
             brain and spinal cord "reorganize" as they learn to provide for
             the substitution; the changes in neurological organization are
             driven by the changes in demand. This mechanism is most successful
             for very specific tasks involving only one of a few areas of the
             brain. However, it can be unsatisfactory if coordination of
             several areas of the brain are required to provide for the
             substituted demand. Thus, the nervous system can accommodate to a
             tendon transplant and result in movement of a joint; however,
             compensatory masquerade is of little use in the control of a
             substituted process for swallowing which involves a number of
             coordinated neurological activities.

             Functional Map Expansion: This mechanism of neuroplasticity
             provides for an area of the "healthy" brain to "grow into" an
             adjacent area of the "damaged" brain that has lost its function.
             The area of growth is usually in the border zone bounding both
             areas. Thus, if a person were to lose his arm, the brain area
             which recognizes the sensation of touch in the arm would no longer
             be functional. The adjacent area of brain recognizing touch on the
             face can send fibers into the arm area. When the face is touched,
             the person perceives touch in both the face and the arm, even
             though the arm has been amputated. When this occurs in the brain's
             motor control system (as in cerebral palsy), it can result in
             contractions of inappropriate muscles in conjunction with a
             purposeful muscle contraction; this double response is not
             desirable. On the plus side, if the healthy area's function is
             minor or related, functional map expansion provides for the
             adjacent healthy area of brain to take over the function of a
             damaged area of brain. Under these conditions, lost function is
             partially restored.

             Homologous Region Adoption: This mechanism of neuroplasticity
             provides for one area of the brain to take over the function of a
             distant area that has been injured. The new functional area can be
             in the same half or in the other half of the brain. (The human
             brain has two halves connected by a bridge. Each half controls
             somewhat different functions, but can share in control of a single
             function). The mechanism involved is thought to be possible
             because of the existence of a minor, but existing neural pathway
             in the distant area which has been non-functional as long as the
             major pathway was in operation. This "uncovering" of existing
             pathways can return some function, but it can be at the cost of a
             decrease in the function of the uninjured part of the brain; the
             uncovered pathway is usually less efficient than the original, no
             longer functional pathway. Also uncovering the substitute pathway
             can interfere with the principle function of that section of the
             brain.

             Cross Model Reassignment: This aspect of neuroplasticity provides
             for one sensory input to replace another. For example: in braille,
             the sense of touch replaces the sense of vision in the "reading
             areas" of the brain. This mechanism resembles compensatory
             masquerade (point 1 above) but generally involves the sensory
             systems (vision, hearing, touch, pain).

             Comments:
             What does this all mean, particularly to a person with a
             disability due to cerebral palsy? It tells us that there are
             mechanisms by which the injured brain can and does rearrange
             itself. Thus, the possibility exists for restoring lost function.
             However, the restoration of a brain function is often at the price
             of impinging upon the quality of another brain function. The
             evidence at this time indicates that in order to restore a
             detailed function, compensatory mechanisms (points 1 and 4 above)
             are more likely to be successful. Points 2 and 3 above can also be
             useful, but generally interfere with other brain functions.

             For the restoration of a broad function involving the coordinated
             interaction of several areas of brain (e.g.: speech and language;
             swallowing), learning how to influence neuroplasticity will
             provide the ultimate answer. Understanding the basic mechanisms of
             neuroplasticity provides the building blocks for achieving this
             goal. In the interim, we are learning: why the methods we use
             successfully, appear to work; how we might improve the success of
             the methods that do work; and why the methods that don't work,
             aren't working.

             © UCP Research & Educational Foundation, February 1997