One of the most fundamental mysteries of the human cortex lies in how 16 billion neurons combine and bind information from many sources into a coherent, coherent experience.
Scientists think that such binding may involve high-frequency oscillations (or “ripples”) that promote neural interaction, similar to rhythms in music and dance. A paper published July 7, 20,22. PNASResearchers from the University of California San Diego School of Medicine offer some of the first empirical evidence showing that such ripples can occur in people.
Think about how you feel when you pet your cat. This includes its appearance, environment, color, movement, sound, and form. You also have to consider your emotions and reactions. Eric Halgren, senior author and professor of radiology at UC San Diego School of Medicine, said that they are all connected in a cohesive whole.
These diverse aspects of the experience can be encoded in different locations on the cortical surface. They are sub-served via their spatiotemporal fire pattern. How activities in these locations connect is the mystery.
Previous research in rodents had shown that hippocampus ripples organize the repetition of these spatiotemporal patterns in sleep. This is critical for making memories permanent.
Halgren led the UC San Diego team that discovered ripples can also be found in all areas of the brain, both in sleep and waking. The ripples were short, lasting approximately one-tenth to a second and having a constant narrow frequency close at 90 cycles per second. A typical short ripple event, according to the authors, could see approximately 5,000 modules become active simultaneously and spread across the cortical surfaces.
This work is part a doctoral thesis in neurosciences written by Charles W. Dickey.
Dickey stated that “Remarkably the ripples co-occurred, and synchronized across both hemispheres and across all lobes, even at great distances.” “Cortical neuron firing was increased during ripples, at ripple rhythm, possibly supporting interaction between distant places.
“There were many co-occurrences that preceded successful memory recall.” This all suggests that cortical coripples encourage the integration of various elements that could make up an experiential memory.
Researchers found that cortical ripples often combine with hippocampal ripples, and embed in slower oscillations (1 to 12 cycles per second). These slower rhythms are controlled by the thalamus (central structure that controls cortical activity levels) and modulate neuronal firing. This is necessary for memory consolidation.
Halgren explained that “as our experience is organized hierarchically and in time,” so too are the rhythms which organize our cortical activities, that create that experience.
This research included analysis of week-long recordings taken directly inside the brains 18 patients to determine the source of epileptic seizures. Research in Halgren’s laboratory continues to show that neuronal firing pattern in different parts the cortex is more predictive during corippling. This is because co-rippling involves the binding letters into words and meanings and actions.
Halgren stated, “Like any other research that expands our understanding about the world’s functioning, it is difficult to predict its practical implications.” Mental fragmentation is a hallmark of schizophrenia, an incurable and common disease. Our findings and others suggest that a certain type of inhibitory inneron is critical for the generation ripples. These cells are known to be selectively affected with schizophrenia. We might be closer to identifying a mechanism for this horrible disease.
Co-authors include: Ilya A. Verzhbinsky, Xi Jiang, Burke Q. Rosen, Sophie Kajfez, Jerry J. Shih and Sharona Ben-Haim, all at UC San Diego; Brittany Stedelin and Ahmed M. Raslan, Oregon Health & Science University; Emad N. Eskandar, Albert Einstein College of Medicine; Jorge Gonzalez-Martinez, Cleveland Clinic; and Sydney S. Cash, Harvard Medical School.