BRAIN REORGANIZATION  [ back to Recovering from a Brain injury ]
While a starfish can regrow an arm that was torn off by a predator, the same is not true of our brains. The injured human brain does not grow new neurons to replace those killed off initially by the traumatic event or subsequently by complications such as brain swelling. Spontaneous brain repair is extremely limited by chemical factors. Proteins naturally occurring in the white matter of the brain (including NoGo, MAG and OMgp) block regrowth of damaged axons. Following brain trauma scavenger cells called astrocytes (a type of glial cell) consume dead and dying brain cells for weeks following TBI. The action of scavenger cells can cause permanent hole or permanent scars in the brain. These holes or scars may or may not be visible on MRI dependent upon their size. They tend not to show up after mild TBI. The larger holes that form after severe brain injury can become sealed off in a fluid filled sac called a hygroma. Research on post-traumatic epilepsy indicates that glial scars left behind by astrocytes can be a trigger for seizures. Experimentation on rats has been underway for decades on use of neuro-protective chemicals to lessen the kill size of brain cells from trauma, and use of nutrients like NGF (Nerve Growth Factor) after the traumatic event to promote healing of damaged brain tissue. These experiments have not reached the point where they have been cleared for use on human beings. We do not know who they would help, to what extent and with what adverse consequences or side effects. The same is true of more recent experimental use of embryonic stem cells injected into rat brains following TBI in hopes of sprouting new brain cells.

The human brain displays a varying amount of "plasticity" which is greatest in infants and young children and least in the elderly. Plasticity refers to the ability of the brain to remodel or reorganize itself in response to stimuli or to injury from trauma, oxygen deprivation or toxic chemicals. Underlying brain plasticity are redundancy and multi-potentiality. Redundancy refers to the extra brain cells and circuits we develop in utero and during infancy as a reserve against future loss. As adults who suffer a TBI, we can put to first real use those extra brain cells and circuits that were laying dormant. Multi-potentiality refers to the capacity of some neural circuitry to serve diverse brain functions. The theory goes that some existing circuits serving a particular function, can be "recruited" to serve a new function following stroke or TBI with prodding in the form of rehabilitation therapies. Plasticity does not depend on growth of new cells, but on changing how given cells and circuits are used in the context of whole brain function.

There is powerful evidence to support the concept of brain reorganization. Some of it is observational. Neurosurgeons who have removed the left half of a child's brain (the speech half) to stop epileptic seizures, have observed that in the years following surgery these children regain normal or near normal speech by developing a new speech center in the surviving right half of the brain. Investigators have shown that following paralysis of one arm after stroke on the opposite side of the brain, if you bind the good arm to the patient's side with a brace, and force him to use his bad arm, the paralyzed arm will begin to move and accomplish simple tasks. Some of the evidence comes from brain scanning techniques. fMRI has been used to show that people with TBI who spontaneously regain lost or diminished brain function, are activating very different parts of their post-injury brain to accomplish the tasks. This helps explain why brain injured people function more slowly and less efficiently and fatigue more quickly; because, they are using more brain sites at farther distances than they used to before injury to accomplish the same tasks.

Plasticity is not just a feature of short term brain response to acute injury. People with chronic brain disorders can improve in some aspects when put through intensive, structured therapy. For example, Parkinson's Disease patients with hypophonia (very soft, nearly inaudible voices) can be taught to speak loudly and keep their volume up through a speech therapy technique known as the Lee Silverman Voice Treatment. When these patients were scanned with PET, the investigators observed that speech initiation had moved from the motor/pre-motor areas of the left hemisphere to the anterior insula, dorso-lateral pre-frontal cortex and basal ganglia in the right hemisphere. See, Neurology 2003; 60(3): 432-440.

The more we know about the brain's potential to reorganize its functions following brain injury (and how to stimulate, induce or guide the reorganization), the more hope exists for improved outcomes following TBI.