So we know that enrichment and learning expands motor maps that correspond to the body part being trained (like the playing hand of string players). What is the consequence of NOT using a part of the body? If you stop speaking for a period of time will brain maps that serve areas of the mouth and tongue shrink or be taken over by neighbouring brain areas?
In amputees, researchers have shown that the area of the brain that formerly represented the missing arm was ‘taken over’ by the adjacent brain cortex that was part of the face map (research by Cohen, Flor). This suggests that removing stimulus to a body part (by amputation) causes a shift in the topographical arrangement of the brain map. Amputation is an extreme example of loss of both sensory input and movement of a body part; is there a body map shift if you don’t use your arm for whatever reason?
In a study published in Science in 1998, Florence and colleagues showed that in monkeys with chronic hand and arm injuries, cortex areas for the face and uninjured upper arm expanded into the cortex representing the damaged limb. This suggests to me that synaptic competition is operating here. When we do not use some capacity that we have, our brains have efficient mechanisms to shift resources to where they are needed. An important question is, how permanent are these brain map rearrangements? Is there a ‘use it or lose it’ rule in place that will rob unused brain maps? Permanency of brain map modification does not make sense to me considering the flexibility and dynamic nature of the healthy brain. The brain is a responsive organ.
Some interesting studies were carried out in the early 1990’s to address the permanency of brain map changes. Brasil-Neto and group showed that when a blood pressure cuff is applied to a person’s arm or leg to temporarily block nerve input to the limb, brain responsiveness to muscles above the cuff increase within a few minutes. This heightened activity goes back to baseline once the cuff is removed. Liepert and colleagues (1995) showed that when someone’s leg is immobilized in a cast after injury, the cortical map representation for the ankle muscle is diminished. However, if the person tries to wiggle their foot, the map activity returns to baseline. This suggests that cortical maps, at least in the normal adult brain, are flexible and responsive. When a body part is missing, injured or immobilized, brain maps shift. When circumstances change, brain maps shift again.
There are possibly a few stages of brain map changes; early and rapid changes involving awakening of dormant synapses or changing the strength of synapses while more permanent changes may involve growing new synapses and dendrites.
I now think about how these facts would be applied to brain injury recovery. During the acute phase of brain injury (days and weeks), shock and inflammation shut down areas adjacent to the injured area. The person may have pretty severe changes in their movements, sensation, thinking, language and emotions during this stage. They try to get going again and are encouraged to do so but they use different muscle groups and rely on body parts not affected by the brain injury. Brain maps likely shift in response, handing over more territory to serve the unaffected body and mind. As shock and inflammation subside, opportunity exists for reorganization around the damaged area and recovery of some of the impaired functions. Perhaps a month has passed…How easy or difficult is it to reverse these initial compensatory brain map changes? Do we (health professionals and families) do a disservice to people after brain injury by encouraging compensatory functions early after brain injury (like using a cane, writing rather than speaking etc.)? Is there untapped capacity for recovery and plasticity that we do not optimize?