HOW TO DEVELOP VERY SMART RATS
STIMULATING THE THINKING CAP THE IMPORTANCE OF THIS QUALITATIVE AND QUANTITATIVE
change in the cortex as a result of environmental enrichment can be seen when we consider a few facts about the cerebral cortex (also called the neocortex). Whatever evolution "means," perhaps its most tangible result is the cortex: it is the end result of the tendency of creatures to develop their ner- vous system as they increase in complexity. In the case of vertebrates, this has meant a steady shift to the top, or the uppermost part of the nervous system. In the earliest verte- brates this meant a swelling of nervous tissue at the top of the spinal cord. As creatures evolved, this swelling increased in size and complexity, including first a hindbrain, then a mid- brain or limbic brain, then a forebrain. Only in higher mam- mals does there develop a new evolutionary structure, the cerebral cortex, which gains in size and importance as we go up the evolutionary ladder.
In rats, the cortex is fairly smooth, and quite small in pro- portion to the lower parts of the brain. In cats and dogs the cortex grows in size, and in order to pack more cortex into the available space there appear crumples and folds called convo- lutions. The relative size of the cortex and its amount of con- volutions increase in apes, and in humans it is deeply convoluted and makes up about 83 percent of the total brain weight.
The neocortex can be visualized as a sheet about two and a half square feet in area (in the case of humans) and less than an eighth of an inch thick, containing about 100 billion neurons, supported and nurtured by many billions of glial cells. Remarkably, these neurons, with their unimaginably rich numbers of interconnections (each neuron with its hundreds or thousands of axonal and dendritic extensions is as complex as a small computer, and each is linked to thousands of other neurons), are virtually all linked only to other neurons in the cortex, with relatively few neurons connecting the cor- tex to the lower brain structures. As brain expert Dr. Eric
32
GETTING SMART: BRAIN EXPANSION THROUGH STIMULATION Harth points out, this means that the incredible interweaving of neural connections largely represents "cortex talking to cortex. This remarkable fact... points to the highly reflective mode of operation of the neocortex. If we were to compare it to a government, it would be analogous to a group of people in lively dispute with one another, but virtually isolated from the outside world."
The cortex is, then, in evolutionary terms, something very new, very different; it is the seat of our so-called higher func- tions. These functions include, in Harm's words, "detection of features in all sensory systems; learning and association of new features and learning of all kinds; memory and recall of sequences of events perceived in the past; patterning of elabo- rate programs of voluntary muscle actions from tying shoe- laces to playing Liszt; formation and understanding of speech; creativity and appreciation in all forms of art, and of course all sensations and consciousness."138
So when we consider the importance of the cortex to every- thing that makes us human, the implications of the studies of Rosenzweig, Diamond, and their colleagues are staggering. Those studies clearly indicate that environmental enrichment, that is, stimulation, or sensory experience, leads to enlarge- ment and other structural changes in the cortex. Since the cortex is the seat of intelligence, then it makes sense to con- clude that environmental enrichment, stimulation, or sensory experience leads to increased intelligence.
Intelligence is, of course, a slippery concept; an animal can prove intelligent when tested for one quality, less intelligent when tested for another. But there are clear indications that there is a strong connection between sensory stimulation and intelligence. Berkeley psychologist David Krech, who with Rosenzweig pioneered the studies of the relationship between mental activity and brain chemistry using rats from different environments, has made a number of studies of the relation- ship between intelligence and experience.
In one experiment he took the two groups of rats which had been selectively bred for many generations, one group for
maze dullness," the other for "maze brightness." It's impor- 33
MEGABRA1N
STIMULATING THE THINKING CAP THE IMPORTANCE OF THIS QUALITATIVE AND QUANTITATIVE change in the cortex as a result of environmental enrichment can be seen when we consider a few facts about the cerebral cortex (also called the neocortex). Whatever evolution "means," perhaps its most tangible result is the cortex: it is the end result of the tendency of creatures to develop their ner- vous system as they increase in complexity. In the case of vertebrates, this has meant a steady shift to the top, or the uppermost part of the nervous system. In the earliest verte- brates this meant a swelling of nervous tissue at the top of the spinal cord. As creatures evolved, this swelling increased in size and complexity, including first a hindbrain, then a mid- brain or limbic brain, then a forebrain. Only in higher mam- mals does there develop a new evolutionary structure, the cerebral cortex, which gains in size and importance as we go up the evolutionary ladder.
In rats, the cortex is fairly smooth, and quite small in pro- portion to the lower parts of the brain. In cats and dogs the cortex grows in size, and in order to pack more cortex into the available space there appear crumples and folds called convo- lutions. The relative size of the cortex and its amount of con- volutions increase in apes, and in humans it is deeply convoluted and makes up about 83 percent of the total brain weight.
The neocortex can be visualized as a sheet about two and a half square feet in area (in the case of humans) and less than an eighth of an inch thick, containing about 100 billion neurons, supported and nurtured by many billions of glial cells. Remarkably, these neurons, with their unimaginably rich numbers of interconnections (each neuron with its hundreds or thousands of axonal and dendritic extensions is as complex as a small computer, and each is linked to thousands of other neurons), are virtually all linked only to other neurons in the cortex, with relatively few neurons connecting the cor- tex to the lower brain structures. As brain expert Dr. Eric
32
GETTING SMART: BRAIN EXPANSION THROUGH STIMULATION Harth points out, this means that the incredible interweaving of neural connections largely represents "cortex talking to cortex. This remarkable fact... points to the highly reflective mode of operation of the neocortex. If we were to compare it to a government, it would be analogous to a group of people in lively dispute with one another, but virtually isolated from the outside world."
The cortex is, then, in evolutionary terms, something very new, very different; it is the seat of our so-called higher func- tions. These functions include, in Harm's words, "detection of features in all sensory systems; learning and association of new features and learning of all kinds; memory and recall of sequences of events perceived in the past; patterning of elabo- rate programs of voluntary muscle actions from tying shoe- laces to playing Liszt; formation and understanding of speech; creativity and appreciation in all forms of art, and of course all sensations and consciousness."138
So when we consider the importance of the cortex to every- thing that makes us human, the implications of the studies of Rosenzweig, Diamond, and their colleagues are staggering. Those studies clearly indicate that environmental enrichment, that is, stimulation, or sensory experience, leads to enlarge- ment and other structural changes in the cortex. Since the cortex is the seat of intelligence, then it makes sense to con- clude that environmental enrichment, stimulation, or sensory experience leads to increased intelligence.
Intelligence is, of course, a slippery concept; an animal can prove intelligent when tested for one quality, less intelligent when tested for another. But there are clear indications that there is a strong connection between sensory stimulation and intelligence. Berkeley psychologist David Krech, who with Rosenzweig pioneered the studies of the relationship between mental activity and brain chemistry using rats from different environments, has made a number of studies of the relation- ship between intelligence and experience.
In one experiment he took the two groups of rats which had been selectively bred for many generations, one group for
maze dullness," the other for "maze brightness." It's impor- 33
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