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Recycle the Plastic: But for how long? — The limits of Neuroplasticity

By Sanah Thakur

Thursday، 07 November 2019 01:09 AM

As human beings living in a dynamic and ever changing environment, we are constantly in contact with a plethora of external factors that directly or indirectly affect us either physically, psychologically or socially. The brain is the one organ in our bodies that is designed to change in response to experience, a phenomenon referred to as ‘plasticity’. Neuroplasticity is derived from the Greek word ‘plastikos’, meaning to form and includes the structural and functional changes in the brain as a result of experience and training. During the initial few years, plasticity of the brain is maximal but continues at a reduced rate throughout life. It is more prominent in certain parts of the brain and certain periods of life in comparison than in others, for example, children are able to recover from brain injuries much better and more completely than adults (Mundkur, 2005). However, a question that is much debated in this field is whether the plasticity of the brain is infinite or limited to some extent. 
There are two sides to this debate; one claiming that once the cognitive structures are established in the critical periods, the components are fixed and flexibility is finished. Damage to any one component can only be compensated by adopting certain behavioural strategies that work around the deficit. The second side postulates that the brain is permanently plastic, as a continuous interaction between the individual and his/her environment results in the formation of functionally specialised structures throughout development. However, though the process of neurogenesis ensures recovery from brain damage to some extent, there are certain limits to plasticity.
With time, the brain remains consistently malleable however the degree of flexibility changes, with the younger brains being more flexible compared to the adult brains. A mentally effortful new experience like acquiring a motor skill, learning a new language or moving through a new environment produces certain changes (increase in synapses, number of neurons or strengthening of connections) in the neural systems that support acquisition of the new skill. This ability to learn new skills remains intact throughout one’s lifespan, however it doesn’t ensure that such training induced changes go beyond the learned skills or promote a healthy brain. 
Despite evidence for neuroplasticity occurring even in adulthood, the damage done by diseases such as Alzheimer’s, Huntington’s, Parkinson’s etc remain unrepairable by the brain. This indicates that there is a certain limit to neuroplasticity, as otherwise brain injury would be overlooked in most situations. The implication of such damage is that the toxicity of the disease processes overrides the brain’s capacity for self-repair or neurogenesis. It occurs throughout the adult life span however much less rapidly in adults. While some of the new neurons that form die almost immediately, some cells are seen to integrate themselves into existing webs of neural connections. New neurons are also observed being produced from stem cells in certain regions of the brain even after the ‘critical period’ of development. However, this process of neurogenesis isn’t always fast enough and sometimes neurons might not also be able to migrate to the areas they are needed, leading to decay. In some cases, brain damage is too extensive for neurogenesis to revive the lost function.
The two conflicting positions on neuroplasticity can be reconciled by analysing the severity and nature of insult, age at the time and other factors like psychosocial context and gender. The relationship between age and damage share a U-shaped effect, with a prenatal injury having the possibility of the poorest outcome (no evidence of transfer of function from injured site to intact tissue) while at the same time plasticity being greater in early childhood, leading to reorganisation and greater sparing of function. On reaching adolescence and adulthood, the same plasticity becomes increasingly less evident. Though severity of damage is of primary importance in the short term, it is the environmental factors that influence nature and rate of recovery from acquired brain damage. Such external factors include family function, access to rehabilitation, socioeconomic status and response to the disability. Gender is also another factor, though the evidence is controversial, as hormonal factors are seen to affect brain development. The female brain appears to have more diffuse organisation due to its rapid speed of development, allowing for greater potential for plasticity and reorganisation of function. Though the brain cannot be stated to have infinite plasticity, it is clear that it isn’t equipotential in a strong sense.
In conclusion, evidence indicates that neuroplasticity is prevalent throughout an individual’s lifespan, however its effectiveness and degree of invasiveness declines with time. Within the field of neuroplasticity there is a lack of consensus on the debate of the brain’s plasticity continuing throughout adulthood, however majority of the research concludes that plasticity is present throughout the lifespan, within certain limits which are subjective to each individual. 

The author can be contacted on Instagram @sincerelysanah

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