In the early stages, the animals could simply memorize which exemplars belonged to each category. After each round, the number of exemplars was doubled. To do this, they measured EEG signals as monkeys learned to assign patterns of dots into one of two categories.Īt first, the animals were shown just two different examples, or “exemplars,” from each category. In the new study, the researchers wanted to investigate whether this activity pattern actually reflects communication between the prefrontal cortex and striatum, or if each region is working independently. “The striatum learns the pieces of the puzzle, and then the prefrontal cortex puts the pieces of the puzzle together.” “The striatum learns very simple things really quickly, and then its output trains the prefrontal cortex to gradually pick up on the bigger picture,” Miller says. Miller’s lab has previously shown that during category-learning, neurons in the striatum become active early, followed by slower activation of neurons in the prefrontal cortex. The paper’s lead author is former Picower Institute postdoc Evan Antzoulatos, who is now at the University of California at Davis. We think synchronized brain waves may be the way the brain does it.” “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. Plasticity doesn’t happen on that kind of time scale,” says Miller, who is a member of MIT’s Picower Institute for Learning and Memory. “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. That process, known as synaptic plasticity, is too time-consuming to account for the human mind’s flexibility, he believes. The phenomenon of brain-wave synchronization likely precedes the changes in synapses, or connections between neurons, believed to underlie learning and long-term memory formation, Miller says. The research team focused on EEG patterns from the prefrontal cortex -the seat of the brain’s executive control system - and the striatum, which controls habit formation. These combined signals generate oscillations known as brain waves, which can be measured by electroencephalography (EEG). There are millions of neurons in the brain, each producing its own electrical signals. 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,” says Earl Miller, the Picower Professor of Neuroscience at MIT and senior author of the study, which appears in the June 12 issue of Neuron. “We’re seeing direct evidence for the interactions between these two systems during learning, which hasn’t been seen before. The researchers found that as monkeys learn to categorize different patterns of dots, two brain areas involved in learning - the prefrontal cortex and the striatum - synchronize their brain waves to form new communication circuits. These quickly changing brain states may be encoded by synchronization of brain waves across different brain regions, according to a new study from MIT neuroscientists. The human mind can rapidly absorb and analyze new information as it flits from thought to thought.
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