have to do with me? These studies all have to do with mam-
mals who are raised in distinct environments from the time they're babies. I'm already an adult, so my brain has already taken on whatever cerebral growth it's ever going to have.
Not so. This assumption that the brain somehow becomes set, like concrete, after a period of youthful plasticity, has
been widespread. Rosenzweig and colleagues even based their
early experiments on it. According to Rosenzweig, "Our ini-
tial studies were of animals placed in the differential environ- ments at weaning... because we supposed that the brain
would be more plastic at weaning than in older rats."281 Says
Marian Diamond, "The general conception in the 1960s, and of course before, was that the brain did not change - that it
3 4
GETTING SMART: BRAIN EXPANSION THROUGH STIMULATION
was a stable structure - and after it developed, it retained its size and eventually decreased."
Soon, however, they began to wonder. If an enriched envi- ronment can alter the brains of young rats, isn't it possible it could also benefit even mature rats? They set about investigat- ing. In one experiment they kept the rats in a standard, non- enriched environment until they were the equivalent of seventy-five years of human age. As Diamond describes it: "The rat has the potential to live 1,000 days, and the human being has the potential to live 100 years. So at 766 days, when we moved some rats to enriched environments, we were three-quarters of the way through the animals' lives.... We found that when they were exposed to an enriched environ- ment between 766 and 904 days of age, even these very old rats showed thickening of the cerebral cortex."225 In test after test the Berkeley researchers found that, in Rosenzweig's words, "The capacity for plastic neural changes was found to be present not only early in life but throughout most if not all of the life span."
While some of the studies have shown that the amount of growth in the cortex is somewhat less and takes more expo- sure to the enriched environment to bring about with advanc- ing age, all the evidence indicates that cortical growth can take place even at extremely advanced ages. What a stunner. Rosenzweig puts it a bit more soberly: "The findings of brain plasticity in adult rats challenged the assumptions of many psychologists and neuroscientists that the brain assumes adult values early in life."281 In fact, the findings met much resis- tance in the scientific community. And no wonder. They seem to challenge not only scientific dogma but even common sense - we have all noticed how as people age they become Wore set in their ways, resistant to change; how adults find it more difficult to open their minds to new ways of thinking than children, as for example in learning a new language.
The implications of the Rosenzweig findings are so vast they're hard to grasp fully. For after all, what they mean is that, provided an environment that is sufficiently enriched (i.e, challenging, stimulating, complex), growth and qualita-
MEGABRA1N
tant to stress that these rats were genetically different, with quite different brains - different levels of brain enzymes, dif- ferent ratios of cortex to subcortex. Krech set out to discover whether environment could change these hereditary differ- ences. A group of maze-bright rats were placed in an impover- ished environment, while a maze-dull group were given an enriched environment. The differences in their brains virtually
disappeared. Similarly, when a maze-bright group was given
an enriched environment while maze-dulls were given an im- poverished environment, the differences doubled.
Krech also tested the rats for another type of intelligence - the ability to learn that rules can change. On this test of "reversal discrimination" the gifted rats always were far supe-
rior to the maze-dull rats. However, when the bright rats were raised in an impoverished environment and the dull rats were given an enriched environment, the dulls proved far superior in performance on the test! Krech's resounding conclusion:
"We can now undo the effects of generations of breeding. Heredity is not enough. All the advantages of inheriting a good brain can be lost if you don't have the right psychologi- cal environment in which to develop it."267
TEACHING OLD RATS NEW TRICKS
WELL, ALL THIS IS INTERESTING, YOU SAY, BUT WHAT DOES IThave to do with me? These studies all have to do with mam-
mals who are raised in distinct environments from the time they're babies. I'm already an adult, so my brain has already taken on whatever cerebral growth it's ever going to have.
Not so. This assumption that the brain somehow becomes set, like concrete, after a period of youthful plasticity, has
been widespread. Rosenzweig and colleagues even based their
early experiments on it. According to Rosenzweig, "Our ini-
tial studies were of animals placed in the differential environ- ments at weaning... because we supposed that the brain
would be more plastic at weaning than in older rats."281 Says
Marian Diamond, "The general conception in the 1960s, and of course before, was that the brain did not change - that it
3 4
GETTING SMART: BRAIN EXPANSION THROUGH STIMULATION
was a stable structure - and after it developed, it retained its size and eventually decreased."
Soon, however, they began to wonder. If an enriched envi- ronment can alter the brains of young rats, isn't it possible it could also benefit even mature rats? They set about investigat- ing. In one experiment they kept the rats in a standard, non- enriched environment until they were the equivalent of seventy-five years of human age. As Diamond describes it: "The rat has the potential to live 1,000 days, and the human being has the potential to live 100 years. So at 766 days, when we moved some rats to enriched environments, we were three-quarters of the way through the animals' lives.... We found that when they were exposed to an enriched environ- ment between 766 and 904 days of age, even these very old rats showed thickening of the cerebral cortex."225 In test after test the Berkeley researchers found that, in Rosenzweig's words, "The capacity for plastic neural changes was found to be present not only early in life but throughout most if not all of the life span."
While some of the studies have shown that the amount of growth in the cortex is somewhat less and takes more expo- sure to the enriched environment to bring about with advanc- ing age, all the evidence indicates that cortical growth can take place even at extremely advanced ages. What a stunner. Rosenzweig puts it a bit more soberly: "The findings of brain plasticity in adult rats challenged the assumptions of many psychologists and neuroscientists that the brain assumes adult values early in life."281 In fact, the findings met much resis- tance in the scientific community. And no wonder. They seem to challenge not only scientific dogma but even common sense - we have all noticed how as people age they become Wore set in their ways, resistant to change; how adults find it more difficult to open their minds to new ways of thinking than children, as for example in learning a new language.
The implications of the Rosenzweig findings are so vast they're hard to grasp fully. For after all, what they mean is that, provided an environment that is sufficiently enriched (i.e, challenging, stimulating, complex), growth and qualita-
MEGABRAIN
tive enrichment of the cerebral cortex can continue throughout adult life. And since the cortex is the seat of the higher func- tions, such as intelligence and creativity, we can suppose that, given the right experiences, intelligence, creativity, and brain size can continue to increase even into extreme old age.