It has been known for some time that increased environmental stimulation usually results in improved performance in animals and humans. Since the 1950s, improved scientific techniques have allowed researchers to demonstrate that this stimulation directly affects the brain cells, thereby showing that the effect goes beyond simply achieving better function.
Studies in this area fall into three major categories: the effects of increased environmental stimulation on normal animals; the effects of decreased stimulation; and, most importantly, the question of whether or not increased stimulation has any effect on recovery of function following brain injury.
Environmental enrichment
Many studies, including those of Rosenzweig and Goldman, show that increased environmental stimulation results in improved performance. Of greater interest are the studies that demonstrate that not only does increased stimulation produce increased abilities, it actually increases brain growth. In these particular studies, rats were put into three different environments for the exact same period of time. The environments were varied according to the amount of stimulation they offered - either normal, deprived or enriched.
At the end of the study period, the rats were tested and, as expected, those that had been in the enriched environment performed significantly better than those in the other two groups. When the rats were sacrificed and their brains studied, a startling revelation was made. Without exception, the rats which had been living in the enriched world had brains that were bigger in weight and dimension, along with increased chemical activity, than the brains of the rats from the other two groups. Thus, increased stimulation had resulted in increased brain growth.
Environmental Deprivation
Gold states that the strongest evidence to support the concept of environmental influence on brain development has come from the studies of selective stimulation or deprivation of a single sense (see note 25 above). The most striking results have been obtained by looking at the effects of deprivation on the visual system. Almost all of these studies show that, with a decrease in visual stimulation, there is a depressive effect on visual function. Also, it was found that the early visual environment can modify the structure and function of connections in various regions of the visual system.
Environmental enrichment following brain injury
One of the first people to investigate this area was Schwartz. He studied four groups of rats - those who received brain injury one day after birth and were then placed in either an enriched or normal environment, and rats without brain injury who were placed in either of the same two environments.
After 120 days, all the rats were tested. It was found that not only did the brain injured rats from the enriched environment perform better than the brain injured ones who had been in the normal environment, but they also did as well as the rats with intact brains who had been in the normal environment. In other words, increased stimulation in these rats after brain injury resulted in normal levels of performance.
This experiment was repeated to see if the enriched conditions following brain injury would affect brain size and chemistry, as well as performance. Since Schwartz had only studied rats injured immediately after birth, the effects on older rats were also investigated. These studies showed that, even though brain injury had occurred, the increased stimulation did in fact produce larger brain weights and increased chemical activity, just as it had done with the normal rats. These same results were also evident in young adult rats - those over 100 days of age.
Thus, following brain injury, the amount of environmental stimulation provided plays a vital role in determining how much brain growth and recovery of function will occur.
Some possible explanations
Will and associates suggest that enriched experience may help to overcome the effects of brain injury in at least three ways:
1 . It results in an increase in the number of connections and pathways in the brain, which may in part take over the functions of the destroyed or damaged tissue.
2. It may protect against the secondary loss of cells in regions away from the injured site-cells that through reorganization may he able to take over function. Their studies showed that the loss of these cells was somewhat smaller in the enriched group.
3. It may promote a compensatory increase in the vital brain chemicals which determine brain growth, since their studies also showed that the measure of these chemicals was larger in the enriched group.