Brain plasticity refers to the changes that occur in the organisation of the brain, and in particular changes that occur to the location of specific information processing functions, as a result of the effect of experience.
The term "cortical plasticity" is more commonly used, however there is no particular restriction of the phenomenon to the cortex.
A common and surprising consequence of plasticity is that the location of a given function can "move" from one location to another in the brain.
The concept of plasticity can be applied to molecular as well as to environmental events. The phenomenon itself is complex and involves many levels of organization. To some extent the term itself has lost its explanatory value because almost any changes in brain activity can be attributed to some sort of "plasticity". Plasticity should be more restricted to adaptive events in the central nervous system rather than merely indicating any change in response to environmental input. For example, after a traumatic brain injury, if the organism can recover to normal levels of performance, that adaptiveness could be considered as a example of "positive plasticity". However, an excessive level of neuronal growth leading to spasticity or tonic paralysis, or an excessive release of neurotransmitters in response to injury which could kill nerve cells, would have to be considered perhaps as a "negative or maladaptive" plasticity.
The main thing to know is that even the adult brain is not "hard-wired" with fixed and immutable neuronal circuits. Many people have been taught to believe that once a brain injury occurs, there is little to do to repair the damage. This is simply not the case and there is no fixed period of time after which "plasticity" is blocked or lost. We simply do not know all of the conditions that can enhance neuroal plasticity in the intact and damaged brain, but new discoveries are being made all of the time. There are many instances of cortical and subcortical rewiring of neuronal circuits in response to training as well as in response to injury. There is now solid evidence that neurogenesis, the formation of new nerve cells, is possible in the adult, mammalian brain--and such changes can persist well into old age.
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