Rosenzweig’s research
Theory: The experiences that a human faces during early development has an effect on the development of the brain
Hypothesis: Animals raised in an enriched (highly stimulating) environment will demonstrate differences in brain growth and chemistry when compared to animals raised in a plain/dull environment
Why use rats? First of all, using humans would be ethically wrong for this experiment. Using rats (versus using another animal) is a better option for many reasons. Their brains are smooth therefore it can be measured and examined more easily after they are killed, they are small and inexpensive and last but not least, large litters allow researchers to also study the role of genetics which is especially useful in nature vs. nuture experiments such as this one.
Methods:
- 12 sets of rats, 3 male rats from the same litter, each of the 3 “brothers” placed in the 3 separate environments
- 3 different environments: the control = with the rest of their colony or in an enriched environment or in an impoverished environment
- treatment period was 4-10 weeks
To avoid bias, the examiners were not told which rat’s brain belonged to which of the 3 environments. After the treatment period, the brains were then measured, weighed and analyzed to determine cell growth and levels of neurotransmitter activity. A neurotransmitter called Acetylcholinesterase was the focus of the chemical aspect of the examination. This neurotransmitter is responsible for faster and more efficient transmission of neural impulses
Results: The cerebral cortex is the part of the brain that responds to experiences, responsible for movement, learning and sensory input, therefore it was the center of the study. It was found to be more heavy and thicker in the enriched environment compared to the other two environments. The brains that inhabited the enriched environment also had increased acetylcholinesterase activity, there were larger neurons (however, no differences between the number of neurons) and the RNA:DNA ratio was higher in the rats that came from the enriched environment. They assumed that this implies higher level of chemical activity had taken place. These results were repeated when they performed the same experiment several more times. The cortex increased in weight in response to experience, but the sub-cortex (the rest of the brain) changed very little. The measurement of the cortex compared to the sub-cortex was the most accurate measurement of all the other measurements because overall brain weight varies with the overall weight of each animal. They also found that enriched synapses were much larger in the rats that came from the enriched environment.
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