Neuroplasticity, also known as neural plasticity, or brain plasticity, is the ability of neural networks in the brain to change through growth and reorganization. These changes range from individual neuron pathways making new connections, to systematic adjustments like cortical remapping. Examples of neuroplasticity include circuit and network changes that result from learning a new ability, environmental influences, practice, and psychological stress.

Neuroplasticity was once thought by neuroscientists to manifest only during childhood, but research in the latter half of the 20th century showed that many aspects of the brain can be altered (or are "plastic") even through adulthood. However, the developing brain exhibits a higher degree of plasticity than the adult brain. Activity-dependent plasticity can have significant implications for healthy development, learning, memory, and recovery from brain d amage.

The term "plasticity" was first applied to behavior in 1890 by William James in The Principles of Psychology. The first person to use the term neural plasticity appears to have been the Polish neuroscientist Jerzy Konorski.

In 1793, Italian anatomist Michele Vicenzo Malacarne described experiments in which he paired animals, trained one of the pair extensively for years, and then dissected both. He discovered that the cerebellums of the trained animals were substantially larger. But these findings were eventually forgotten. The idea that the brain and its function are not fixed throughout adulthood was proposed in 1890 by William James in The Principles of Psychology, though the idea was largely neglected. Until around the 1970s, neuroscientists believed that the brain's structure and function was essentially fixed throughout adulthood.

While the brain was commonly understood as a nonrenewable organ in the early 1900s, Santiago Ramón y Cajal, father of neuroscience, used the term neuronal plasticity to describe nonpathological changes in the structure of adult brains. Based on his renowned Neuron doctrine, Cajal first described the neuron as the fundamental unit of the nervous system that later served as an essential foundation to develop the concept of neural plasticity. He used the term plasticity in reference to his work on findings of degeneration and regeneration in the central nervous system after a person had reached adulthood, specifically. Many neuroscientists used the term plasticity only to explain the regenerative capacity of the peripheral nervous system, which Cajal's conceptual transfer of the term gave rise to a controversial discussion.

The term has since been broadly applied:

Given the central importance of neuroplasticity, an outsider would be forgiven for assuming that it was well defined and that a basic and universal framework served to direct current and future hypotheses and experimentation. Sadly, however, this is not the case. While many neuroscientists use the word neuroplasticity as an umbrella term it means different things to different researchers in different subfields ... In brief, a mutually agreed upon framework does not appear to exist.

Applications and examples

The adult brain is not entirely "hard-wired" with fixed neuronal circuits. 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 evidence that neurogenesis (birth of brain cells) occurs in the adult, mammalian brain—and such changes can persist well into old age. The evidence for neurogenesis is mainly restricted to the hippocampus and olfactory bulb, but current research has revealed that other parts of the brain, including the cerebellum, may be involved as well. However, the degree of rewiring induced by the integration of new neurons in the established circuits is not known, and such rewiring may well be functionally redundant.

There is now ample evidence for the active, experience-dependent re-organization of the synaptic networks of the brain involving multiple inter-related structures including the cerebral cortex. The specific details of how this process occurs at the molecular and ultrastructural levels are topics of active neuroscience research. The way experience can influence the synaptic organization of the brain is also the basis for a number of theories of brain function including the general theory of mind and Neural Darwinism. The concept of neuroplasticity is also central to theories of memory and learning that are associated with experience-driven alteration of synaptic structure and function in studies of classical conditioning in invertebrate animal models such as Aplysia.

Regards,
Jack

Submit manuscript at: https://www.scholarscentral.org/submissions/clinical-experimental-neuroimmunology.html

E-mail attachment at: manuscripts@omicsonline.com