Researchers have recently made significant strides in understanding how the brain processes and integrates information, addressing a long-standing enigma in neuroscience.
For many years, scientists believed that the brain processes information in a hierarchical structure, with various regions dedicated to specific functions. Nevertheless, the way these regions communicate and merge information to create a unified understanding has remained unclear. Now, a team at the University of California San Diego School of Medicine has made substantial progress in unveiling this mystery by studying how neurons synchronize across the human brain while reading text. Their findings are detailed in Nature Human Behavior and form part of the doctoral thesis by Jacob Garrett, a candidate at UC San Diego School of Medicine.
“Understanding how the brain’s activity relates to our conscious experiences is one of the key unresolved questions in modern neuroscience,” stated senior study author Eric Halgren, Ph.D., a professor in the Departments of Neurosciences and Radiology at UC San Diego School of Medicine. “When you read, your brain must transform letters into a word and then connect it to a concept or an object. Our research supports the idea that this is achieved through synchronous activation across multiple brain regions.”
This synchronization, referred to as “co-rippling,” is believed to be vital for tying various pieces of information together to create a clear understanding. In rodent studies, co-rippling has been seen in the hippocampus, which is responsible for memory formation. In humans, Halgren and his colleagues have previously demonstrated that co-rippling also happens across the entire cerebral cortex.
To investigate the mechanics of co-rippling, Ilya Verzhbinsky, an M.D./Ph.D. candidate in UC San Diego’s Medical Scientist Training Program, conducted a study published in the Proceedings of the National Academy of Sciences, focusing on what happens at the level of individual neurons firing in different cortical areas during ripples. The current study broadens the scope, exploring how the billions of neurons in the cortex coordinate their firing to process information effectively.
“With 16 billion neurons in the cortex—double the global population—the brain functions like a massive choir that must be organized to produce a unified sound,” explained Halgren. “Just as a choir must sing in harmony, our neurons need to work together to create a single thought or action. Co-rippling resembles neurons performing in tune and rhythm, enabling us to integrate information and make sense of our surroundings. When ripples occur, about two-thirds of neuron pairs in the cortex synchronize, delivering a surprisingly powerful effect.”
Observing co-rippling in humans has been challenging due to the limitations of noninvasive brain imaging. To overcome this hurdle, the researchers employed intracranial electroencephalography (EEG), which captures the brain’s electrical activity from within the skull. The study focused on 13 patients with drug-resistant epilepsy, who were already being monitored with EEG as part of their treatment, allowing a deeper analysis of brain activity than typical noninvasive methods permit.
Participants viewed a series of animal names mixed with strings of random consonants or nonsensical words and then pressed a button to indicate the animal name they saw. During these evaluations, the researchers identified three cognitive stages: an initial phase where visual processing occurred in the cortical areas without conscious awareness; a second phase where information was “seeded” into other cortical areas via co-ripples for more complex processing; and a final phase where co-ripples facilitated the integration of this information into conscious awareness and a behavioral response—pressing the button.
Throughout this exercise, co-rippling was observed among various brain regions involved in these cognitive processes, with even stronger rippling when participants read actual words.
The implications of these findings could be significant for addressing neurological and psychiatric disorders, such as schizophrenia, which are marked by disruptions in how information is processed and integrated.
“By better understanding how typical minds integrate information, it may become easier to discover ways to help reintegrate minds affected by these disorders,” Halgren remarked.
Overall, this study contributes to a broader understanding of the connection between brain function and human experience.
“This inquiry touches on a fundamental aspect of human life, highlighting the relationship between mind and brain,” Halgren stated. “Gaining insights into how our brain’s neurons collaborate can lead us to a better understanding of consciousness itself.”
Other co-authors involved in the study include Erik Kaestner at UC San Diego School of Medicine, Chad Carlson at the Medical College of Wisconsin, Werner K. Doyle and Orrin Devinsky at New York University Langone School of Medicine, and Thomas Thesen at Geisel School of Medicine.
The research received funding from the National Institutes of Health (grants MH117155, T32MH020002) and the Office of Naval Research (grant N00014-16-1-2829).
