Brain waves synchronize 'in order to learn'

Brain waves synchronize 'in order to learn'

Researchers from the Massachusetts Institute of Technology have published new findings in the journal Neuron on how the human brain can rapidly absorb and analyze new information.

"Brain waves" are oscillations produced by the combined electrical signals of millions of neurons. The Massachusetts Institute of Technology (MIT) researchers found that, when monkeys are learning to categorize different patterns of dots, the brain waves from two regions involved in learning synchronize to form new communication circuits.

In these category-learning tasks, the scientists had previously shown that neurons in one of these brain regions - the striatum, which controls habit formation - become active first, and are then followed by the slower activation of neurons in the prefrontal cortex, which is the brain's executive control system.

Next, the researchers wanted to see whether this staggered activation is the result of communication between the two regions, or if they are simply working independently. To test this, they used electroencephalography (EEG) to measure brain waves in monkeys as the animals learned to sort patterns of dots into categories

To begin with, the monkeys were shown just two different examples ("examplars") from each of the two categories of dots. The number of exemplars shown to the monkeys was doubled after each round.

Eventually, at the point at which they were no longer able to memorize which specific exemplars belonged to which category, the monkeys began to understand the traits that characterized the two categories.

By the end of the task, the monkeys could be shown 256 unique exemplars and categorize all of them correctly.

Brain forms unique circuits specific to categories learned

While the monkeys were learning the task, the researchers monitored shifts in the animals' EEG patterns. In particular, they noticed that at the point where the monkeys transitioned from simply memorizing the dots to understanding the categories, the scientists saw new brain wave patterns, known as "beta bands," correspond with the adoption of the new thinking process.

The researchers used electroencephalography to measure brain waves in monkeys as the animals learned to sort patterns of dots into categories.

These beta bands, though produced independently by the striatum and prefrontal cortex, began to synchronize. Earl Miller, the picower professor of neuroscience at MIT and senior author of the study, says that this shows the two regions are communicating.

"There is some unknown mechanism that allows these resonance patterns to form, and these circuits start humming together," he says. "That humming may then foster subsequent long-term plasticity changes in the brain, so real anatomical circuits can form. But the first thing that happens is they start humming together."

Interestingly, as the monkeys became confident at sorting the dots into categories, the researchers noticed two separate circuits form that connected the striatum and prefrontal cortex - each corresponding to one of the categories.

These circuits would undergo further modification as more information relating to the categories is received and interpreted by the animals.

Prof. Miller explains that the prefrontal cortex learning the categories "isn't the end of the game." To Miller, these constantly updating circuits typify "the open-ended nature of human thought. You keep expanding your knowledge."

"We're seeing direct evidence for the interactions between these two systems during learning, which hasn't been seen before," he says. "Category-learning results in new functional circuits between these two areas and these functional circuits are rhythm-based, which is key because that's a relatively new concept in systems neuroscience."

He adds:

If you can change your thoughts from moment to moment, you can't be doing it by constantly making new connections and breaking them apart in your brain. Plasticity doesn't happen on that kind of time scale.

There's got to be some way of dynamically establishing circuits to correspond to the thoughts we're having in this moment, and then if we change our minds a moment later, those circuits break apart somehow. We think synchronized brain waves may be the way the brain does it."

The MIT researchers are now examining how the brain learns more abstract information, and how this abstraction is reflected in the activity of the striatum and prefrontal cortex.

Earlier this week, reported on a study published in the journal Science that found sleep strengthens memory after learning.

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