GETTING SMART: BRAIN EXPANSION THROUGH STIMULATION

themselves, "If the rats run mazes differently, do they have a different brain chemistry?"

More generally, they wondered how the brain's chemistry was changed by various types of mental activity. They hy- pothesized that mental activity, particularly learning and mem- ory, would result in higher levels of a certain brain enzyme (acetylcholinesterase, or AChE). To test this, they took labora- tory rats with different levels of AChE in their brains and compared how they performed on problems that required mental activity (such as maze running). They found that the rats with higher levels of AChE learned better than those with low levels: the maze-bright rats had higher levels of AChE than the maze-dull rats.

Then they decided it would be interesting to approach the problem from the opposite direction, by making rats perform problems that required mental activity, and seeing whether different types of performance produced different levels of AChE. In other words, since there was a chemical difference in the brains of bright and dumb rats, could you change that chemistry by designing the rats' environment in a different way? That is, could you alter brain chemistry and structure by altering the environment?

To perform this experiment, they needed to have groups of rats whose lives had required of them differing levels of men- tal activity. Thus, the researchers took a pool of rats which through many years of controlled laboratory breeding had been made genetically equal, and divided them randomly at weaning into three different groups. Each group was placed in a different environment. The first group was placed in ordi- nary laboratory cages, three rats to each plain wire-mesh cage. This was called the standard environment. The second group was placed in isolation, each rat held 1. solitary confinement in a cage with three opaque walls, dim lights, little noise, a minimum of stimulation, and no chance to interact with other rats. This was called an impoverished environment. The third group was raised in "play groups" of ten to twelve rats, in a large, well-lit, multileveled cage filled with swings, slides, ladders, bridges, an assortment of toys, frequently changing

MEGABRAIN

were developed, scientists made the discovery that apparently brain cells, called neurons, do not reproduce themselves. In! other words, the absolute number of one's brain cells is deter- mined from infancy, and no matter what experiences or stimu-; lations the brain receives, the number of brain cells could not increase. In this the neurons are unlike the other cells of the body, which can reproduce many times - if a muscle cell is damaged or destroyed it can be replaced by a new cell; it is i this capability that is exploited by body builders, whose large muscles are the result of the repair and regeneration of muscle cells damaged or destroyed by strenuous exercise. No wonder scientists found it hard to conceive of any way brain structure and function could be changed by sensory input. No wonder our scoffer finds it hard to believe in brain machines that can be used like body-building devices, stimulating the brain and triggering brain growth and increases in mental powers.

HOW TO DEVELOP VERY SMART RATS

THEN CAME A SERIES OF EXPERIMENTS BY BIOLOGICAL psy-

chologists Mark Rosenzweig and colleagues at the University of California, Berkeley, that were so unexpected in their im- plications that they were, for many scientists, unbelievable. When it became clear that the controversial studies were being widely replicated by numerous independent researchers, initial disbelief and skepticism turned to universal acceptance, yet; the studies remain revolutionary and astounding in their impli- cations.

The studies started out innocently enough. Back in the 1920s, a Berkeley psychologist had noticed that some rats were better at running mazes than other rats. He had specifi- cally chosen and bred generation after generation of "maze- bright" rats, and another strain of genetically bred "maze-dull" rats. Some forty years later these strains of rats were still reproducing in the Berkeley labs. Mark Rosenzweig and asso- ciates David Krech and Mark Bennett, who were interested in the relationship between brain chemistry and learning, asked |

26

GETTING SMART: BRAIN EXPANSION THROUGH STIMULATION

themselves, "If the rats run mazes differently, do they have a different brain chemistry?"

More generally, they wondered how the brain's chemistry was changed by various types of mental activity. They hy- pothesized that mental activity, particularly learning and mem- ory, would result in higher levels of a certain brain enzyme (acetylcholinesterase, or AChE). To test this, they took labora- tory rats with different levels of AChE in their brains and compared how they performed on problems that required mental activity (such as maze running). They found that the rats with higher levels of AChE learned better than those with low levels: the maze-bright rats had higher levels of AChE than the maze-dull rats.

Then they decided it would be interesting to approach the problem from the opposite direction, by making rats perform problems that required mental activity, and seeing whether different types of performance produced different levels of AChE. In other words, since there was a chemical difference in the brains of bright and dumb rats, could you change that chemistry by designing the rats' environment in a different way? That is, could you alter brain chemistry and structure by altering the environment?

To perform this experiment, they needed to have groups of rats whose lives had required of them differing levels of men- tal activity. Thus, the researchers took a pool of rats which through many years of controlled laboratory breeding had been made genetically equal, and divided them randomly at weaning into three different groups. Each group was placed in a different environment. The first group was placed in ordi- nary laboratory cages, three rats to each plain wire-mesh cage. This was called the standard environment. The second group was placed in isolation, each rat held 1. solitary confinement in a cage with three opaque walls, dim lights, little noise, a minimum of stimulation, and no chance to interact with other rats. This was called an impoverished environment. The third group was raised in "play groups" of ten to twelve rats, in a large, well-lit, multileveled cage filled with swings, slides, ladders, bridges, an assortment of toys, frequently changing

MEGABRAIN

stimuli, and a variety of challengers. This was called an enriched environment.

After certain periods ranging from days to a number of months, the brains of the rats were removed and analyzed. The researchers discovered that rats raised in the enriched en- vironment showed higher levels of AChE activity in then- brain cortex than did rats raised in the standard and impover- ished environments. (The cerebral cortex is a layer of nerve cells forming a convoluted outer shell over the brain, the "thinking cap" or "gray matter" atop the brain, in which much of the thinking or higher intellectual activity of the brain takes place.) Says Rosenzweig, "Rather than cortical AChE activity being a fixed individual characteristic, as we had supposed, it could apparently be altered by experience!"281

Since AChE activity was related to learning ability, that is, the ability to process information, this meant that the rats in the enriched environment had more learning ability - were "smarter" - than the other rats, despite the fact that they had all started out as equals. Somehow, experiences had altered intelligence.

HIGHLY STIMULATED EINSTEINIAN RATS