The second effect of an environment on physiological processes that will be discussed is brain plasticity. This is the brain’s ability to rearrange its connections with its neurons. This translates to the idea that the structure of the brain changing as a result of exposure to different environments. Two studies that support the idea that the brain is effected by the environment include: Maguire's study on spatial navigation and its effect on the hippocampus, and Rosenzweig and Bennett's study on deprivation versus enrichment and its effect on rat brains.
In Rosenzweigs and Bennets (1972) study, rats were placed in two different environments. The independent variable was the type of environment the rats were exposed to. One environment was stimulating which contained enrichment items such as toys and the other was deprived with no form of entertainment. These rats spent about 30-60 days in their respective environments and were killed at the end for a post-mortem study. This allowed researchers to dissect and measure the cortexes. The results were that rats that lived in the stimulating environment had a thicker cerebral cortex and heavier frontal lobe than the rats that lived in the deprived environment. This experiment, while demonstrating that a rat’s brain is literally shaped by the environment, is not 100% conclusive as it lacks ecological validity. Even though rats may be mammals, the findings cannot be wholly generalized to humans as the brain and environmental inputs differ between humans and animals such as rats. This doesn’t mean that the experiment isn’t useful - it only means that it has a limitation that needs to be developed upon with further studies that directly relate to the human brain.
Another experiment that fits the role of further studies would be Maguire et al. (2000). Maguire investigated whether or not the hippocampus played a role in human spatial memory such as memorizing and learning. This correlational study included London taxi drivers with a range of age/experience and MRI scanning to assess how their brains differed to the control group. The results demonstrated produced by the scans showed significantly more grey matter in both left and right hippocampi of the taxi drivers compared to the control group. For the control group, the pixel counting revealed a larger anterior right hippocampus than the left and larger body of the hippocampus on the right than the left than in taxi drivers, but the posterior hippocampus was larger in taxi drivers than in controls. Maguire’s experiment establishes a very strong correlation between the use of spatial memory and the hippocampus, as it is the first study that shows brain plasticity in humans. In essence, it adds to Rosenzweigs study.
That’s not to say this is a perfect experiment. It is important to recognize that this is a correlational study, which means there are no definite causations. A minor uncertainty that should be noted relates to the nature vs. nurture debate: did the driving influence the change in the hippocampus or did their larger than average hippocampus lead them to become taxi drivers? Correlation may not be causation in this bidirectional ambiguity problem. To fully confirm her findings, Maguire would theoretically have to take 40 guys and force 20 of them to learn “the Knowledge” test and measure the hippocampus before that. This form of longitudinal study would not be time efficient, as it would take an incredibly long time of 1 to 2 years. It is simply something that could be expanded upon in order to further develop Maguire’s original study. Despite this limitation, Maguire’s experiment is convincing as she also conducted other tests by looking at the brain scans of bus drivers and trainee taxi drivers to vary her subjects so that it wouldn’t be limited to only a certain group. In the end her study was groundbreaking as her finding showed that physiological processes do affect human brain plasticity.
In conclusion, the two discussed effects of the environment on physiological processes are enrichment on brain plasticity and climate effects on melatonin and behavior. With evidence provided by supporting studies and theories, it can be stated that there is a bidirectional relationship between the environment and physiological processes.
by
lizarrdo (student)
