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Thursday, March 10, 2005

NATURAL SELECTIONS

CEREBRAL TRAINING

Glimpsing the 'big picture' at the heart of gray matter


It is a commonly held belief that we don't tap into the full power of our brains. Self-help gurus make millions by exploiting this belief, separating people from their money by making them think there is a secret to tapping mysterious, unused reserves of brain power.

"This is a fallacy that comes from the early days of neuroscience," said Earl Miller, professor of neuroscience at the Picower Center for Learning and Memory at the Massachusetts Institute of Technology.

"Early maps of the brain only had a few things labeled because we did not know much about the rest. People falsely thought that this meant that the rest was untapped potential."

Miller should know -- his work is aimed at uncovering how the brain learns, and how it is "trained" to do different tasks. For example, we learn to stop at a red stoplight without having to consciously think about it. How?

Scientists used to think that it was the cerebral cortex, the crowning glory of the human brain, that learned decision rules like "stop at red" and "go at green," and then transferred this knowledge to the more primitive lobes in the forebrain known as the basal ganglia, under the cortex.

It's like an executive in a top-floor office delegating small amounts of power to a menial worker down below.

But Miller and colleague Anitha Pasupathy found that the menial workers are a lot smarter than scientists thought. As their results published in the journal Nature last month show, by simultaneously recording neural activity from the prefrontal cortex and the striatum (the input structure of the basal ganglia) as monkeys learned new rules, they found that the striatum learned faster than the more highly evolved prefrontal cortex.

In the worker analogy, this is equivalent to the workers learning the new rule, and then instructing the executive upstairs.

"These findings suggest new ways of thinking about learning," Miller said. "They suggest that new learning isn't simply the smarter bits of our brain such as the cortex 'figuring things out.' Instead, we should think of learning as interaction between our primitive brain structures and our more advanced cortex. In other words, primitive brain structures might be the engine driving even our most advanced, high-level, intelligent learning abilities," he said.

The prefrontal cortex is where the self sits, the "I." It is the "thinking" part of the brain and is highly developed in humans. So it is only natural to imagine that when we learn new things, the prefrontal cortex figures them out first and then, once they are routine, delegates the tasks to the more primitive, subcortical basal ganglia.

The new study turns this idea around.

So what does it tell us about nonhuman brains? Does it mean that animals without a highly developed prefrontal cortex might nevertheless be "smarter" than we imagined?

"Of course, this depends on what we mean by 'smart,' " said Miller. "Animals without a highly developed prefrontal cortex are capable of learning some very complex behaviors, but they tend to be very stereotyped; the behaviors are always done the same way and always in the same situation."

Having a developed prefrontal cortex means that an animal has the ability to adapt and modify its behavior when circumstances change.

"A major difference between human thought and animal thought is that more advanced animals get the 'big picture' easily, whereas less advanced animals do not," said Miller, who explained with a story about monkeys he'd once trained to perform a simple matching task.

"The monkeys saw two color patches one after another. If they were the same color -- we used red, green and blue -- the monkeys had to pull a lever to indicate a match. Monkeys learned this by trial and error."

Once the monkey had learned, the researchers switched to three new colors. What happened?

"The monkeys had no idea what to do with the new colors," said Miller. "They hadn't learned the 'big picture' -- the concept of matching. Instead, they had simply memorized all 36 possible combinations of stimuli."

The difference is that humans, with a more developed prefrontal cortex, easily get the big picture.

However, the big picture of the brain itself is still a long way off. It is yielding its secrets, but slowly.

In Ian McEwan's new novel, "Saturday," the protagonist Perowne, a neurosurgeon, is contemplating that future day when the secret of consciousness has been laid bare. "But even when it has," Perowne thinks, "the wonder will remain, that mere wet stuff can make this bright inward cinema of thought, of sight and sound and touch bound into a vivid illusion of an instantaneous present, with a self, another brightly wrought illusion, hovering like a ghost at its center."

As for the medical benefits of Miller's work, they too lie in the future: "We think that autism and other neuropsychiatric diseases could come from a lack of balance in the interactions between the basal ganglia and the frontal cortex," he said. "It will take further research to determine how to test for and correct this. But, it's a start."

"Saturday," by Ian McEwan, is published by Jonathan Cape. A book of Natural Selections columns translated into Japanese, "Nou to sekkusu no seibutsugaku (Evolution, Sex and the Brain)," is published by Shinchosha. Rowan Hooper is a biologist at Trinity College, Dublin. He welcomes readers' questions and comments at rowan.hooper@tcd.ie


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