Rosenzweig, Bennet & Diamond (1972)
Rosenzweig, Bennet & Diamond carried out a classic study of neuroplasticity. You can use this study for the following learning objectives:
Explain how principles that define the biological level of analysis may be demonstrated in research.
Discuss how and why particular research methods are used at the biological level of analysis.
Discuss ethical considerations related to research studies at the biological level of analysis.
Discuss two effects of the environment on physiological processes
In this classic study, Rosenzweig, Bennet & Diamond wanted to see if changing the level of stimuli in the environment would result in physical changes in the brain. Neuroplasticity refers to the ability of the brain to change as a result of one's experience. Before this research was done, scientists believed that the brain changed up until a critical period in childhood. After that, no changes in the brain were believed possible.
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.
Three male rats from a common litter were randomly allocated to one of three environments. 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 typically spent 30 to 60 days in their respective environments before they were killed in order for the researchers to study changes in the brain's anatomy.
The anatomy of the brain was different in the EC and the IC. There was an increased thickness and higher weight of the cortex in EC rats compared to that of IC rats. 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, which is an important neurotransmitter for learning and memory.
It appears that the thickness of the cortex and the overall weight of the brain increased as a result of the enriched environment. Follow-up to this research indicated that just 30 minutes a day in an enriched environment produced the same changes in the brain in rats as had been observed in the original experiment where rats were exposed to the EC condition for a much longer period of time.
One variable that was not clear in the enriched environment is whether it was the environment (the toys) or the social activity. Putting rats alone in large cages with toys for two hours a day showed no effect. The single rat tended not to play with the objects and instead rested and groomed himself. The enriched environment produced cerebral changes in a single rat only if the rat was stimulated to interact with the objects.
Since brain plasticity is assumed to follow the same pattern in both animals and humans, 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.
- The experiment was a highly controlled laboratory experiment so it was possible to establish a cause and effect relationship.
- The experiment used animals, so it may be difficult to generalize to humans unless research with humans provides the same results.
- In the enriched environment it could have been exercise that made a difference, rather than "stimulation." It is still not clear from the enriched environment how the variables of social interaction, environmental stimulation and exercise may interact.
- The research results have been replicated many times.
- There is the ethical consideration of undue stress or harm to the animals in the study. Not only were some rats isolated and put into an impoverished environment, but they were killed at the end of the study. A cost benefit analysis should demonstrate that the goals of the study are worth the harm done to the animals.