More Experience Bigger Brain AAQ

The question of whether certain experiences produce physical changes in the brain has been a topic of conjecture and research among philosophers and scientists for centuries. By the 1960s, new technologies had been developed that gave scientists the ability to measure brain changes with precision using high-magnification techniques and assessment of levels of various brain enzymes and neurotransmitter chemicals. Mark Rosenzweig and his colleagues Edward Bennett and Marian Diamond, at the University of California at Berkeley, incorporated those technologies in an ambitious series of 16 experiments over a period of 10 years to try to address the issue of the effect of experience on the brain. The main hypothesis implicit in Rosenzweig's research was the idea that animals raised in highly stimulating environments will demonstrate differences in brain growth and chemistry when compared with animals reared in plain or dull circumstances.

In each of the experiments, 12 sets of 3 male rats, each set from the same litter, were studied. Three male rats were chosen from each litter. They were then randomly assigned to one of three conditions. One rat remained in the laboratory cage with the rest of the colony or the standard condition (SC), another was assigned to the enriched condition (EC) cage, and the third was assigned to the impoverished condition (IC) cage. Thus, 12 rats were placed in each of these conditions for each of the 16 experiments (that's 576 rats).

The three different environments were described as follows: 1. The standard laboratory colony cage contained several rats in an adequate space with food and water always available. 2. The impoverished environment was a slightly smaller cage isolated in a separate room in which the rat was placed alone with adequate food and water. 3. The enriched environment was virtually a rat's Disneyland (no offense intended to Mickey!). Six to eight rats lived in a large cage furnished with a variety of objects with which they could play. A new set of rat toys, from a selection of 25 objects, was placed in the cage each day, so the enriched rats experienced a lot of variety or play activities. The rats were allowed to live in these different environments for various periods of time, ranging from 4 to 10 weeks. The rats were housed in clean, adequately sized cages and provided with food and water. Following this differential treatment period, the experimental rodents were humanely euthanized and examined to determine if any differences had developed in brain development. To be sure that no experimenter bias would occur, the examinations were done in random order by code number so that the person doing the autopsy would not know in which condition the rat was raised in order to avoid any unintentional bias. The rats' brains were then measured, weighed, and analyzed to determine the amount of cell growth and levels of neurotransmitter activity. In this latter measurement, one brain enzyme was of particular interest: acetylcholinesterase (abbreviated AChE). This brain chemical is important because it allows for faster and more efficient transmission of impulses among brain cells.

Results indicated that the brains of the enriched rats were indeed different from those of the impoverished rats in many ways. The cerebral cortex (the part of the brain that responds to experience and is responsible for movement, memory, learning, and sensory input: vision, hearing, touch, taste, and smell) of the enriched rats was significantly heavier and thicker. Rats in the enriched environment (EC) showed a higher mean weight of the cerebral cortex, which was significantly greater compared to those in standard (SC) and impoverished (IC) environments. The mean weights were 1.25 grams for EC rats, 1.10 grams for SC rats, and 0.95 grams for IC rats. Additionally, the cerebral cortex thickness was also increased in EC rats compared to the other groups, with mean thicknesses of 150 micrometers for EC rats, 140 micrometers for SC rats, and 130 micrometers for IC rats. The differences in both cortical weight and thickness between EC and IC rats were statistically significant, with p-values of less than 0.01 and 0.05, respectively. Also, greater activity of the nervous system enzyme acetylcholinesterase was found in the brain tissue of the rats with the enriched experience. Although no significant differences were found between the two groups of rats in the number of brain cells (neurons), the enriched environment produced larger neurons. These differences reached statistical significance (p < 0.05).

Rosenzweig and his colleagues stated that "although the brain differences induced by environment are not large, we are confident that they are genuine. When the experiments are replicated, the same pattern of differences is found repeatedly.... The most consistent effect of experience on the brain that we found was the ratio of the weight of the cortex to the weight of the rest of the brain: the sub-cortex. It appears that the cortex increases in weight quite readily in response to experience, whereas the rest of the brain changes little" (p. 25). This measurement of the ratio of the cortex to the rest of the brain was the most accurate measurement of brain changes because the overall weight of the brain may vary with the overall weight of each animal. By considering this ratio, such individual differences are canceled out. Figure 1.2 illustrates this find - ing for all 16 studies. As you can see, in only one experiment was the difference not statistically significant. The researchers reported a finding relating to the two rat groups' brain synapses (the points at which neurons meet). Most brain activity occurs at the synapse, where a nerve impulse is either passed from one neuron to the next so that it continues on, or it is inhibited and stopped. Under great magnification using the electron microscope, the researchers found that the synapses of the enriched rats' brains were 50% larger than those of the impoverished rats, potentially allowing for increased brain activity.