Animal Experiments and the Brain

There is ample evidence in the literature to demonstrate that the structure and function of the brain are to a large extent determined by the way it is used and educated. By sacrificing their brains during controlled experiments, this has already been proven in the animal kingdom.

Although no conclusions on human learning or functioning can be drawn from experiments on animals, it is nevertheless interesting to take note of such experiments, because they seem to confirm that learning does indeed change brain structure.

Professor Klosovskii, a neurosurgeon in Moscow, took newborn litters of kittens and puppies and divided them into two exactly equal groups, one as the experimental group and the other as the control group. The kittens and puppies in the control group were permitted to grow in the usual way in which kittens and puppies normally grow. The experimental animals, however, were placed on a slowly revolving turntable and lived there throughout the experiment. The only difference in what happened to each of the groups was that the experimental group experienced a moving world while the control group experienced only as much as newborn kittens and puppies normally do. When the animals were ten days old, Klosovskii began to sacrifice matched pairs of the puppies and kittens to take their brains. The last of them were sacrificed by the nineteenth day of life. The animals on the turntable had from 22.8 percent to 35 percent (one third) more growth in the vestibular areas of their brains than did the animals in the control group. Just what does more growth mean? Did Klosovskii see one-third larger number of brain cells in his microscope? Not at all; he saw the same number of brain cells but one third larger and one third more mature.

Mark Rosenzweig and his associates have shown that the brains of rats raised in an “enriched” laboratory environment — in a large cage containing many fellow rats and playthings that could be explored and manipulated — differed markedly in a number of respects from rats raised in small, isolated cages. The rats in the enriched environment had a greater weight and thickness of cerebral cortex than the ones raised in isolation. The researchers found more spines — which often serve as receivers in synaptic contacts — on the dendrites of cortical neurons in rats from enriched environments. Synaptic junctions in rats from enriched environments averaged about 50 percent larger than those in rats raised in isolation, and synaptic contacts were more frequent in the rats from enriched environments.

The researchers wondered which of the many stimuli in the enriched environment had the most effect on the development of the rats' brains. Further experiments brought surprising findings to light. Exercising and physical activity had no effect in terms of enriching their brains; visual stimulation wasn't necessary to create enriched brains, as demonstrated by blind rats; handling and petting had no effect; whether the rats were together or isolated didn't matter; and teaching the rats to press a lever helped only a little. The experimenters found only one aspect that helped to enrich the rats' brains — the freedom to roam a large, object-filled space. Rats appear to be able to develop a good “space-brain” (one that helps them locate points in space and objects to climb over or through) rather than a “reasoning brain.” Or, as David Krech, one of the experimenters put it, “For each species there exists a set of species-specific experiences that are maximally enriching and maximally efficient in developing its brain.”