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Early experimental work on neuroplasticity was conducted by an eighteenth-century Italian scientist, Michele Malacarne, who discovered that animals made to learn tasks would develop larger brain structures Rosenzweig, The first theoretical notions of neural plasticity were developed in the nineteenth century by William James , a pioneer of psychology.
James wrote about this topic in his book The Principles of Psychology James, Progress of the idea — modern theories: Modern experimental instruments like imaging tools have yielded enough information to develop improved theories. Scientists now think that neuroplasticity occurs throughout all life stages, having extensive capacities from childhood development through healing diseases Doidge, The brain can rearrange itself in terms of the functions it carries out, as well as in terms of the basic underlying structure Zilles, Functional plasticity is the brain's ability to move functions from a damaged area of the brain after trauma, to other undamaged areas.
Existing neural pathways that are inactive or used for other purposes take over and carry out functions lost because of the injury. After brain injury such as accidents or stroke, the unaffected brain areas can adapt and take over the functions of the affected parts. This process vary in speed but it can be fast in the first few weeks phase of spontaneous recovery then it becomes slower.
It can be helped by rehabilitation, and the nature of rehabilitation programmes varies with the type of injury from retraining some types of movement to speech therapy. There are ways through which brain plasticity can enable brain-damaged people to regain some of their past capacities. Each of the approaches through which the nervous system adapts its functionality has differences in terms of how it occurs, as well as in which patients it occurs.
Functional plasticity can occur through a process termed axonal sprouting, where undamaged axons grow new nerve endings to reconnect the neurons, whose links were severed through damage.
Undamaged axons can also sprout nerve endings and connect with other undamaged nerve cells, thus making new links and new neural pathways to accomplish what was a damaged function. Although each brain hemisphere has its own functions, if one brain hemisphere is damaged, the intact hemisphere can sometimes take over some of the functions of the damaged one.
In homologous area adaptation, brain behavior becomes active in the equivalent part on the opposite side of the brain from where it usually occurs Grafman, If it normally occurs on the right side, then it would instead move to the left side, and vice versa.
This functional neuroplasticity occurs more often in children than in adults. Shifting over a module to the opposite side displaces some of the functionality that was originally there. Cross-modal reassignment occurs when the brain uses an area that would normally process a certain type of sensory information such as sight for a different type of sensory information instead such as sound.
When a brain region does not receive sensory data as expected, say because a person has become blind, this brain region may become repurposed for another sense, like touch.
In map expansion, the brain notices that a certain area gets extensive use, so it expands this area Grafman, This is comparable to how the body can notice that certain muscles get more use such as those involved in an often-played sport , then grows those muscles larger.
When a person often engages in an activity or experience, this produces enlargement of the associated brain region.
The brain growth occurs right away, so that neuroscientists can detect it through brain imaging technologies while it occurs Grafman, Compensatory masquerade involves the brain reusing a component to conduct a mental operation other than what it would typically do. Case studies of stroke victims who have experienced brain damage and thus lost some brain functions have shown that the brain has an ability to re-wire itself with undamaged brain sites taking over the functions of damaged brain sites.
Thus, neurons next to damaged brain sites can take over at least some of the functions that have been lost. A youth with a right parietal lobe injury wound up with the left parietal lobe taking over some functions normally occurring on the right side.
The youth then had difficulty with tasks normally occurring on the left side, because some right-side equivalents had taken over left-side brain resources Grafman, Neuronal Unmasking:.
However, when brain damage occurs these synapses can become activated and open up connections to regions of the brain that are not normally active and take over the neural function that has been lost as a result of damage. Structural neuroplasticity is the brain's ability to change its physical structure as a result of learning, involving reshaping individual neurons nerve cells.
During infancy, the brain experiences rapid growth in the number of synaptic connections. As each neuron matures, it sends out multiple branches, this increases the number of synaptic contacts from neuron to neuron. At birth, each neuron in the cerebral cortex has approximately 2, synapses. By the time a child is three years old, the number of synapses is approximately 15, synapses per neuron Gopnick, et al. This process continues throughout our life.
Part of the development of the vision system is genetically hardwired. However, another part of this development depends on neuroplasticity. As a child grows, the incoming information from light sources, such as light reflected off the faces of caregivers, provides necessary cues for the brain to adjust its growth patterns. The equivalent plasticity-based growth also occurs with the other senses, calibrating the young person to local conditions. The development of language reveals even more about neuroplasticity.
Again, part of this functionality is genetically hardwired, but part depends on feedback from the environment. An individual has certain nerve cells programmed to become grammar modules.
For these to function correctly, they require the input of specific grammatical rules from a culture, such as the rules of English or Spanish. Thus, neuroplasticity enables the brain to process language.
New neural connections, different densities of nerve cells, varying strengths of neural connections. How does neuroplasticity work? At the most basic level, it starts with the production of a new nerve cell neurogenesis. Then, individual neurons develop new connections to each other. A neuron works by sending or receiving electrochemical signals with other neurons in the brain.
The way that individual neurons connect to each other controls how the signals get sent, like the routing of messages over the internet or of instructions codes in a computer processor. As each neuron develops connections to others, this results in growing clusters of cells. The neurons can adjust the level or strength of signal with connecting neurons. This ongoing process provides fine-tuning of the neural architecture.
Rewiring larger regions, reorganizing the nervous system at multiple levels. Neurons work together at several different levels. Not only individual cells, but even clumps within brain regions can grow in greater or lower density.
As cells grow or die in different regions, the relative densities vary. Such variations can provide an even broader adjustment or neuroplasticity in the brain than individual nerve cell connections.
When nerve bundles become broken, through injury or surgery, the brain can regrow these elements Doidge, Surprisingly, the brain can reconnect itself in an efficient manner even to deal with sizable upsets. It operates like a plant, able to regrow around lost parts. Gradually, the repairs extend through subcortical layers, reaching larger-scale cortical levels of the brain. This growth occurs throughout the nervous system, including the spine and distributed branches, not only in the brain.
Recurring synaptic connections grow more efficient cell assembly theory. The nerve connections grow stronger when one cell fires before the other, rather than when they both fire simultaneously.
Sequential firing produces a causal relationship, enabling the nervous system to learn. This is something that is predetermined by your genes.
For example, there is an area of the brain that is devoted to movement of the right arm. Damage to this part of the brain will impair movement of the right arm. In other words, neuroplasticity is not synonymous with the brain being infinitely malleable. In a study of Caenorhabditis elegans , a type of nematode used as a model organism in research , it was found that losing the sense of touch enhanced the sense of smell.
This suggests that losing one sense rewires others. As in the developing infant, the key to developing new connections is environmental enrichment that relies on sensory visual, auditory, tactile, smell and motor stimuli.
The more sensory and motor stimulation a person receives, the more likely they will be to recover from brain trauma. For example, some of the types of sensory stimulation used to treat stroke patients includes training in virtual environments, music therapy and mentally practising physical movements. The basic structure of the brain is established before birth by your genes. But its continued development relies heavily on a process called developmental plasticity, where developmental processes change neurons and synaptic connections.
In the immature brain this includes making or losing synapses, the migration of neurons through the developing brain or by the rerouting and sprouting of neurons.
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