Neuroplasticity can be defined as brain’s ability to change, remodel and reorganize for purpose of better ability to adapt to new situations. Neural networks are not fixed, but occurring and disappearing dynamically throughout our whole life, depending on experiences. While we repeatedly practice one activity such as a sequence of movements or a mathematical problem, neuronal circuits are being formed, leading to better ability to perform the practiced task with less waste of energy. Once we stop practicing a certain activity, the brain will redirect these neuronal circuits by a much known ‘use it or lose it’ principle. Neuroplasticity leads to many different occurrences, such as habituation, sensitization to a certain position, medication tolerance, even recovery following brain injury. Neuroplasticity also occurs hand-in-hand with synaptic pruning, which is the brain's way of deleting the neural connections that are no longer necessary or useful and strengthening the necessary ones. How your brain decides which connections to prune out depends on your life experiences and how recently connections have been used. In much the same way, neurons that grow weak from underuse die off through the process of apoptosis. Apoptosis is defined as the death of cells which occurs as a normal and controlled part of an organism's growth or development. Two well-known research studies into neuroplasticity were conducted by Maguire et al. (2000) and Rosenzweig & Bennet (1972).
Maguire et al (2000) examined the role of extensive navigational experience on the shape and size of the hippocampus. The study conducted was a qausi-experiment using a single blind method where the researches did not know which group the brains the were measuring came from. The sampling method was through volunteering and from those volunteers 16 right-handed male taxi drivers who passed the knowledge test to become a full driver were selected, with the target population being those with extensive navigational experience. Taxi drivers were selected as they were theorised to have extensive navigational experience. 50 right-handed males were used as a control group. MRI’s were used to measure the brains using VBM for a measure of density and pixels for size of the hippocampi. Researchers found that the posterior hippocampi were larger in the taxi drivers while the anterior hippocampi were larger in the control group. There was also a positive correlation with years’ experience and density of the hippocampus. As there was a difference in the size of the hippocampus between the two groups, it can be concluded that the experience of the taxi drivers directly caused the changes in their hippocampi.
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Although the research was limited by sampling considerations, it was well controlled giving it good internal validity. A small sample limits external validity because the results most likely will not be normally distributed and thus cannot represent the target population. The strengths of the research are that both the variables and bias were well controlled. The variable of interest was control by the research through the use of the Knowledge Test. As the sample was exclusively male and right-handed, the control participants were also controlled for these two variables. Likewise, the use of the single blind research design meant that researcher bias was controlled. On the other hand, although researcher bias was well controlled, there are some limitations of the research in regard to gender and culture representations. The sample was exclusively male and right-handed and therefore cannot be generalised without caution to female and/or left-handed individuals. In addition, as the sample was collected solely from London taxi drivers, some caution needs to be used when generalising outside of the sample. The research design was a quasi/natural experiment as the independent variable, navigational experience, could not be manipulated. Therefore, it can be assumed that extensive navigational experience would be found in individuals with who have to ‘navigate’ as a part of their everyday life. Therefore, with the limitations of the sample noted above taken into consideration, the sample can be considered to represent the target population. Although replication of the study with a more balanced sample would increase the validity of the research in support of the theory, all in all, the research carried out by Maguire et al. provides credible evidence in support of the theory of neuroplasticity.
A study that investigates the effects of a deprived or an enriched environment on neuroplasticity is an experiment conducted by Rosenzweig & Bennet (1972). The aim of the study was to investigate whether environmental factors such as a rich or an impoverished environment would affect the development of neurons in the cerebral cortex. In the experiment, male rats were chosen from different litters to be randomly allocated to three different conditions: In the control condition (CC) there were three rats in the cage. In the impoverished condition (IC), the researchers placed each rat in individual cages. The individual cages lacked the toys and the maze which were in the enriched environment. For the enriched condition (EC), the researchers placed 10 - 12 rats in a cage containing different stimulus objects to explore and play with. All groups had free and adequate access to food and water. The rats were kept in these condition for 30-60 days before being killed to study changes in the brain’s anatomy. The scientist conducting the autopsy and studying the brain did not know what condition the rat came from as to assist with validity. The rats in the enriched environment had a heavier frontal lobe and thicker cortex compared to the rats in the deprived environment. The researchers also noted that rats in the EC condition had developed significantly greater activity in the neurons in the cerebral cortex associated with transmission of acetylcholine. This may have resulted from the exposure to the toys in the stimulating environment, which helped to develop neural connections in the rat’s brain.
Since rats and humans are similar, brain-wise, the implications of the study are that the human brain should also be affected by environmental factors such as intellectual and social stimulation. It is now known that poverty is a major risk factor in children’s cognitive development as poverty is related to a number of risk factors such as poor nutrition, lack of access to good education and poor health. As Rosenzweig used rats for the experiment, it is difficult to generalise the findings to humans. There is also an ethical consideration on the cause of undue harm and stress onto the rats during the study. However, as it was a single blind study, and that there were numerous follow-up studies, the experiment has overall good validity. Rosenzweig’s experiments have had a significant impact on psychology as they clearly show that there is a cause and effect between the environment and brain development.
Neuroplasticity is the brain's ability to reorganize itself by forming new neural connections throughout life. Neuroplasticity allows the neurons in the brain to compensate for injury and disease and to adjust their activities in response to new situations or to changes in their environment. There are also limits to neuroplasticity being that its limited, but the strengths outweigh its weakness allowing the brain to retain much more important knowledge for longer. Neuroplasticity is a credible because it effectively explains behaviour and brain structure and has a number of applications. Within the theory itself, however, further research is required to uncover its aspects that are still unclear and to overcome its limitations.
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