WE MUST REMEMBER, OF COURSE, THAT THESE ARE STUDIES OF
animals other than humans, so it's possible that their conclu-sions can't be applied generally to humans. However, as the studies have progressed from rats to squirrels to monkeys, whose brains are very similar to human brains, the results have remained consistent. Also, it's significant that the part of the brain altered by an enriched environment is the cortex, which grows not only in absolute size, but in its ratio to the rest of the brain. While rats have small cortex-to-subcortex ratios, some 83 percent of the total weight of human brains is in the cortex. So it makes sense to think that the relative ef-fects of environmental enrichment compared to lack of stimu-lation would have even more pronounced effects in humans than in rats - after all, the cortex plays a much greater role in human affairs than in rat affairs. We don't know what effect varied environments like those the Berkeley rats experienced have on rat creativity, rat philosophy, rat wisdom, rat intu-ition, and so on; but since human life is powerfully influenced by these products of our "higher," which is to say cortical, faculties, substantial cortical growth could have an enormous impact on human consciousness and human evolution.
But, you point out, these rats experienced cerebral devel-opment as a result of being raised, or spending large amounts of their life, in this so-called enriched environment. Granted that an enriched environment or increased environmental complexity, challenge, and stimulation might lead to human brain growth - the whole point is moot, since no human, would agree to being confined for long periods of time to a
36
GETTING SMART: BRAIN EXPANSION THROUGH STIMUIATION
controlled environment, no matter how "enriched."
If it were the case that the enrichment effect required long periods of exposure, this would be true. However, the re-search of Rosenzweig and his colleagues at Berkeley has proved that cortical change can happen much more easily and rapidly than they had initially thought. First they found that keeping the rats in the enriched cage for only two hours a day resulted in just as much brain growth as keeping them in the cage all day.
Argentinian researchers created a "super-enriched" envi-ronment and found that it caused as much brain growth in four days as took place in thirty days in the ordinary enriched envi-ronment of the Berkeley group. Later they found that four daily one-hour periods of enriched exposure significantly in-creased cortical growth. Then they went on to find that four daily exposures of only ten minutes to an enriched environ-ment brought significant increases in cortical weight!101 Other investigators found that a single forty-five-minute session of learning to choose lighted alleys to avoid shock has resulted in significant brain changes, such as increase in the number and shape of some synapses.281 As researchers become increas-ingly sophisticated, they are discovering that even very short exposures to an enriched environment can have significant and long-lasting effects on the cortex. And what's more, these brain changes can happen rapidly - in some cases structural changes in the brain are evident within seconds of sensory stimulation!
In another series of experiments, scientists demonstrated that when neurons in the brains of lab rats are electrically stimulated, new synapses are formed within seconds, dramati-cally increasing the number of synapses per neuron. Neurobi-ologist William Greenough of the University of Illinois at Champaign-Urbana is one of many brain scientists intrigued by these experiments. "This is the most extraordinary case of structural plasticity encountered so far in the brain sciences,"
says Greenough. He asked himself if there was a relationship between increased brain capacity, represented by a growth of new synapses, and memory. To answer this question he
de-37
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.
PRESTO CHANGO: THE BRAIN AS QUICK-CHANGE
WE MUST REMEMBER, OF COURSE, THAT THESE ARE STUDIES OF
animals other than humans, so it's possible that their conclu-sions can't be applied generally to humans. However, as the studies have progressed from rats to squirrels to monkeys, whose brains are very similar to human brains, the results have remained consistent. Also, it's significant that the part of the brain altered by an enriched environment is the cortex, which grows not only in absolute size, but in its ratio to the rest of the brain. While rats have small cortex-to-subcortex ratios, some 83 percent of the total weight of human brains is in the cortex. So it makes sense to think that the relative ef-fects of environmental enrichment compared to lack of stimu-lation would have even more pronounced effects in humans than in rats - after all, the cortex plays a much greater role in human affairs than in rat affairs. We don't know what effect varied environments like those the Berkeley rats experienced have on rat creativity, rat philosophy, rat wisdom, rat intu-ition, and so on; but since human life is powerfully influenced by these products of our "higher," which is to say cortical, faculties, substantial cortical growth could have an enormous impact on human consciousness and human evolution.
But, you point out, these rats experienced cerebral devel-opment as a result of being raised, or spending large amounts of their life, in this so-called enriched environment. Granted that an enriched environment or increased environmental complexity, challenge, and stimulation might lead to human brain growth - the whole point is moot, since no human, would agree to being confined for long periods of time to a
36
GETTING SMART: BRAIN EXPANSION THROUGH STIMUIATION
controlled environment, no matter how "enriched."
If it were the case that the enrichment effect required long periods of exposure, this would be true. However, the re-search of Rosenzweig and his colleagues at Berkeley has proved that cortical change can happen much more easily and rapidly than they had initially thought. First they found that keeping the rats in the enriched cage for only two hours a day resulted in just as much brain growth as keeping them in the cage all day.
Argentinian researchers created a "super-enriched" envi-ronment and found that it caused as much brain growth in four days as took place in thirty days in the ordinary enriched envi-ronment of the Berkeley group. Later they found that four daily one-hour periods of enriched exposure significantly in-creased cortical growth. Then they went on to find that four daily exposures of only ten minutes to an enriched environ-ment brought significant increases in cortical weight!101 Other investigators found that a single forty-five-minute session of learning to choose lighted alleys to avoid shock has resulted in significant brain changes, such as increase in the number and shape of some synapses.281 As researchers become increas-ingly sophisticated, they are discovering that even very short exposures to an enriched environment can have significant and long-lasting effects on the cortex. And what's more, these brain changes can happen rapidly - in some cases structural changes in the brain are evident within seconds of sensory stimulation!
In another series of experiments, scientists demonstrated that when neurons in the brains of lab rats are electrically stimulated, new synapses are formed within seconds, dramati-cally increasing the number of synapses per neuron. Neurobi-ologist William Greenough of the University of Illinois at Champaign-Urbana is one of many brain scientists intrigued by these experiments. "This is the most extraordinary case of structural plasticity encountered so far in the brain sciences,"
says Greenough. He asked himself if there was a relationship between increased brain capacity, represented by a growth of new synapses, and memory. To answer this question he
de-37
MEGABRAIN
cided to see if this almost instantaneous brain growth can hap-pen not only in response to electrical stimulation but also in response to learning and experience. He taught a group of rats to master a number of mazes over a period of three and a half weeks, then microscopically examined their brains. He found pronounced increases in their cortical dendrites, compared to no increases in control rats.
Next, he fitted rats with tiny opaque contact lenses. By covering one eye and then teaching them to run mazes, he was able to compare the growth of one side of the brain with the other. He found increased dendritic branching and increased synapses in the brain hemisphere that received the sensory input from the eye with vision. The equation was clear: more information, more synapses. What's more, experiments with infant, adult, and even very old rats showed this same rapid-brain-growth effect. Greenough's work suggests that an indi-vidual's experience can cause new neuronal connections to spring up quickly and systematically, exactly where they are needed: "synapses on demand."
"We can offset and even reverse late brain aging in rats by providing changes in experiences on a regular basis," con-cludes Greenough. "It's known that old rats lose synapses, and old people do, too. Are they lost because they're forming fewer connections? There's a good possibility that experience can govern the number of synapses that are born and the number of synapses that survive."133
If this kind of significant structural change can happen as a result of brief stimulation in a rat's cortex, surely the much larger, more responsive, more powerful human cortex should similarly respond to certain types of "enrichment," that is, stimulation, or challenge, or complexity, with significant structural changes - i.e., growth - in the cortex. These struc-tural changes should result in increases in the functioning of the cortex, which means increases in intelligence, creativity, and all those other higher faculties that reside in the cortex.
WHEN WE USE THE FRUITS OF THIS RESEARCH TO THINK ABOUT
the human brain, with its much more powerful and important 38
GETTING SMART: BRAIN EXPANSION THROUGH STIMULATION
cortex, it make sense that humans who are exposed to enriched environments - that is, humans whose brains are challenged and stimulated - should experience changes in the shape, size, and structure of the cortex. These changes should result in enhanced cortical function, including increased intel-ligence, creativity, and so on. Very short exposures to stimula-tion can bring about these changes. That is, it's likely that short periods of intense brain stimulation can increase brain complexity and capacity for humans of any age. As David Krech predicted with characteristic audacity more than fifteen years ago, "I foresee the day when we shall have the means, and therefore, inevitably, the temptation, to manipulate the behavior and the intellectual functioning of all people through environmental and biochemical manipulation of the brain."65
And how could this environmental manipulation of the brain take place? One possibility is by using any of a variety of machines designed by scientists to expose the human neo-cortex to stimuli and experiences which are novel, changing and challenging, and which provide the brain an opportunity to exercise itself by means of self-observation, self-transfor-mation, and learning. These mind machines, many scientists now believe, can be the adult human counterpart to the swings, slides, bells, ladders, and flashing lights of the lab rats' enriched environment.
39
MEGABRAIN
cided to see if this almost instantaneous brain growth can hap-pen not only in response to electrical stimulation but also in response to learning and experience. He taught a group of rats to master a number of mazes over a period of three and a half weeks, then microscopically examined their brains. He found pronounced increases in their cortical dendrites, compared to no increases in control rats.
Next, he fitted rats with tiny opaque contact lenses. By covering one eye and then teaching them to run mazes, he was able to compare the growth of one side of the brain with the other. He found increased dendritic branching and increased synapses in the brain hemisphere that received the sensory input from the eye with vision. The equation was clear: more information, more synapses. What's more, experiments with infant, adult, and even very old rats showed this same rapid-brain-growth effect. Greenough's work suggests that an indi-vidual's experience can cause new neuronal connections to spring up quickly and systematically, exactly where they are needed: "synapses on demand."
"We can offset and even reverse late brain aging in rats by providing changes in experiences on a regular basis," con-cludes Greenough. "It's known that old rats lose synapses, and old people do, too. Are they lost because they're forming fewer connections? There's a good possibility that experience can govern the number of synapses that are born and the number of synapses that survive."133
If this kind of significant structural change can happen as a result of brief stimulation in a rat's cortex, surely the much larger, more responsive, more powerful human cortex should similarly respond to certain types of "enrichment," that is, stimulation, or challenge, or complexity, with significant structural changes - i.e., growth - in the cortex. These struc-tural changes should result in increases in the functioning of the cortex, which means increases in intelligence, creativity, and all those other higher faculties that reside in the cortex.
WHEN WE USE THE FRUITS OF THIS RESEARCH TO THINK ABOUT
the human brain, with its much more powerful and important 38
GETTING SMART: BRAIN EXPANSION THROUGH STIMULATION
cortex, it make sense that humans who are exposed to enriched environments - that is, humans whose brains are challenged and stimulated - should experience changes in the shape, size, and structure of the cortex. These changes should result in enhanced cortical function, including increased intel-ligence, creativity, and so on. Very short exposures to stimula-tion can bring about these changes. That is, it's likely that short periods of intense brain stimulation can increase brain complexity and capacity for humans of any age. As David Krech predicted with characteristic audacity more than fifteen years ago, "I foresee the day when we shall have the means, and therefore, inevitably, the temptation, to manipulate the behavior and the intellectual functioning of all people through environmental and biochemical manipulation of the brain."65
And how could this environmental manipulation of the brain take place? One possibility is by using any of a variety of machines designed by scientists to expose the human neo-cortex to stimuli and experiences which are novel, changing and challenging, and which provide the brain an opportunity to exercise itself by means of self-observation, self-transfor-mation, and learning. These mind machines, many scientists now believe, can be the adult human counterpart to the swings, slides, bells, ladders, and flashing lights of the lab rats' enriched environment.
39