The coordinated activity of brain cells, like birds flying in formation, helps us behave intelligently in new situations, according to a study led by Cedars-Sinai researchers. The work, published in the peer-reviewed journal Nature, is the first to elucidate the neurological processes known as abstraction and inference in the human brain.
“Abstraction allows us to ignore irrelevant details and focus on the information we need to act, and inference is the use of knowledge to make informed assumptions about the world around us,” said Ueli Rutishauser, PhD, professor and Board of Governors Chair in Neuroscience at Cedars-Sinai and co-corresponding author of the study. “Both are important parts of cognition and learning.”
Humans often use these two cognitive processes together to learn quickly and act appropriately in new environments. An example of this is an American driver renting a car in London for the first time.
“The British drive on the right side of the car and the left side of the road, which is the opposite of what we do in the U.S.,” Rutishauser said. “For someone from the U.S., driving in London means reversing many of the rules they’ve been taught, and making that mental shift requires abstraction to focus on lateral driving and making inferences to avoid merging directly into oncoming traffic.”
In the study, researchers worked with 17 hospitalized patients who had electrodes surgically implanted in their brains as part of a procedure to diagnose epilepsy. In total, the researchers recorded the firing of thousands of brain cells as the participants performed an inference task on a computer.
Observing the activity of so many brain cells required the use of artificial intelligence to extract the relevant responses, allowing researchers to see the coordination between neurons during successful inference.
“These are high-dimensional geometric shapes that we can’t imagine or visualize on a computer monitor,” said Stefano Fusi, PhD, a principal investigator at Columbia University’s Zuckerman Mind Brain Behavior Institute and co-corresponding author of the study. “But we can use mathematical techniques to visualize simplified renditions of them in 3D.”
During the recordings, participants were repeatedly shown four images — a person, a monkey, a car, and a watermelon. In response to each image, they were asked to press a button with either their left or right hand. The subjects were then given a “correct” or “incorrect” message.
Through repetition, participants eventually learned the correct response for each of the four images. At this point, the rules of the game were reversed without participants being informed, and the opposite response for each image was counted as correct.
After the switch, some participants were able to quickly figure out the rule change and infer the correct answers without relearning them, meaning they performed inference.
The researchers saw striking geometric patterns in the brains of these participants. Groups of neurons were firing together, much like birds flying in formation or a crowd of people spontaneously singing at a sporting event. The way the neurons coordinated their activity and encoded the relevant information indicated that the subjects had acquired the conceptual knowledge needed to perform the task. The researchers saw no such patterns in the brains of participants who were unsuccessful in using inference.
“Building conceptual knowledge is an important aspect of learning,” said Hristos Courellis, PhD, a Cedars-Sinai researcher and first author of the study. “In our study, we identified a neural basis for this process, which in cognitive psychology is called abstraction.”
Some subjects were initially unable to make inferences from experience with the task alone. For these subjects, the investigators provided verbal instructions that allowed the subjects to then infer the correct answers.
“A remarkable finding was that the same neural geometries emerged in participants who received verbal instructions as in those whose ability to infer was based on experiential learning,” said Adam Mamelak, MD, director of the Functional Neurosurgery Program and professor of Neurosurgery at Cedars-Sinai and a co-author of the study. “This crucial finding shows that verbal input can result in neural representations that would otherwise take a long time to learn through experience.”
The study, which drew on data from Cedars-Sinai and the University of Toronto, was led by Cedars-Sinai and conducted as part of a multi-institutional consortium funded by the National Institutes of Health. Brain Research Through the Advancement of Innovative Neurotechnologies Initiative, or The BRAIN Initiative.
“This study provides new insights into how our brains enable us to learn and perform tasks flexibly and in response to changing conditions and experiences,” said Merav Sabri, PhD, program director for The BRAIN Initiative. “These insights build on a body of knowledge that may one day lead to interventions for neurological and psychiatric conditions involving memory and decision-making deficits.”
One surprise for the researchers was the discovery that these specific patterns of brain activity emerged only in the hippocampus, a region in the center of the brain that is known to be crucial for the formation of new long-term memories.
“Our discovery expands our knowledge about the role of the hippocampus in learning,” Rutishauser said. “This is the first direct demonstration of the human hippocampus’ involvement in learning abstract knowledge and inferential behavior. Many neurological conditions, including Alzheimer’s disease, obsessive-compulsive disorder and schizophrenia, affect this brain region, and our discovery may help explain the impaired decision-making we see in these patients.”
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