Neural Plasticity Evidence From Numerous

Neural Plasticity

Evidence from numerous studies make a strong case for a relationship between brain plasticity and behavioral change, thus it is clear that experience alters the synaptic organization of the brain in species as diverse as fruit flies and humans, and although evidence that these changes are functionally meaningful is more difficult to collect, there is little doubt that changes in synaptic organization are correlated with changes in behavior (Whishaw Pp).

Therefore, animals with extensive dendritic growth, relative to untreated animals show facilitated performance on numerous types of behavioral measures in contrast to animals with atrophy in dendritic arborization that show a decline in behavioral capacity (Whishaw Pp). Similarly, factors that enhance dendritic growth, nerve growth factor, facilitate behavioral outcome, while factors that block dendritic growth, brain injury at birth in rats, retard functional outcomes (Whishaw Pp). Although studies have stressed that changes in dendritic morphology, there are multiple, and likely dissociable, changes in the neuron morphology that correlate behavioral change, including "increases in dendritic length, dendritic branching pattern, spine density, synapse number, synapse size, glial size and number, and metabolic activity" (Whishaw Pp).

According to current studies, dendrites in the cortex may show a net proliferation, regression, or stability depending upon several factors that affect behavior, thus it seems likely that a net proliferation of dendrites is a response to an increased availability of afferent supply, while the net reduction in dendrites, seen in response to injury for example, is likely to reflect a decline in the afferent supply to a cell (Whishaw Pp). From this view, "dendrites are hypothesized to be in a state in which they are constantly ready to expand or retract their territory, limited largely by availability of afferent nourishment and by the metabolic capacities of the cell" (Whishaw Pp).

There is little evidence that the infant or adult brain is capable of growing new projections over long distances, thus "it seem most likely that changes in afferent supply reflect changes in axonal arborizaiton of relatively nearby neighbors" (Whishaw Pp). One recent study examined the patterns of connections of pyramidal cells, which are the almost exclusive outputs of the neocortex, and found that approximately 70% of the excitatory synapses on any layer pyramidal cell are derived from pyramidal cells in the near vicinity (Whishaw Pp). Therefore, the fact that neurons can expand their field of influence means that if neurons die, remaining ones could enlarge their field to make up for some of the lost processing power (Whishaw Pp).

The concept of neural plasticity is central to the work of psychiatrists and psychotherapists because how they help people change involves enabling their patients' minds to develop new pathways for self-regulation that can enable them to live more rewarding lives (Beychok Pp). Whether the community utilizes the power of interpersonal relationships alone to heal and promote growth or combine this crucial aspect of clinical work with pharmacological tools to aid in therapeutic process, the community is attempting to harness the natural capacity of the brain to change in response to new conditions (Beychok Pp).

Peter Huttenlocher offers a comprehensive overview of the science of plasticity and how the most evolved part of the brain changes in response to experience (Beychok Pp). His review of research, both basic and clinical, highlights important principles of neural plasticity and the limits of present understanding (Beychok Pp). Among the principles outlined by Huttenlocher are:

More than half of our genes directly influence brain development; this is especially prevalent as a factor in utero and in the early years of life;

Plasticity involves the development of synapses, myelination, synaptic pruning and even the growth of new neurons;

Plasticity has both positive aspects (adapting to environmental changes) and negative aspects neural circuits can compete with each other for specificity of function and crowd out other functions);