BIOLOGICAL LIMITS TO HEALING TBI [ back to What's New ]
Compared to adults, the neural plasticity of the child's brain is vastly superior. There are many clinical cases on record in which a neurosurgeon removed the entire left hemisphere of a severely epileptic child, who went on to speak normally because all his language functions were transferred to and taken over by his remaining right hemisphere. Such a thing is utterly impossible in an adult. Why? When the adult brain loses a pocket of nerve cells from trauma, glial cells migrate to the area and create a glial scar which acts as a physical barrier to rewiring and reorganization of surviving brain tissue. Experimentation with grafts of healthy brain tissue into the space left behind by dead neurons has failed largely because of glial scarring. Recent research has shed light on the reason for this. The developing human embryo undergoes an explosive proliferation of neurons which migrate along genetically predetermined paths with the assistance of glial cells which act as a kind of scaffolding. When they reach their targets, they begin hooking up with (synapsing with) other brain cells in response to genetic coding and experience. Some of these connections are normal and adaptive (useful), while others are abnormal and maladaptive. During late embryonic development and early childhood, the human brain undergoes a kind of self-pruning of maladaptive neural connections. The failure of this pruning process to occur as it should is believed to be a factor in the genesis of schizophrenia. Recent research indicates that certain glial cells (those containing a substance called chondroitin sulfate) block axons from sprouting new connections which would be harmful to the organism. These glial cells continue to be produced into adulthood, and continue to block axonal regeneration following brain trauma. Neuroscientists are now at the point where they can breed glial cells in vitro without the protein which inhibits new growth of damaged axons. These could be injected into a damaged brain. Such experiments will now occur in rats for a long time before they are attempted in humans.