The fundamental mystery of the human cortex is how its 16 billion neurons integrate or bind different types of information to encode into a single, consistent, integrated experience or memory.
Scientists hypothesize that such connections include high-frequency vibrations or “ripples” that promote neural interactions, similar to the rhythms of music and dance. In a treatise published on July 7, 2022 PNASResearchers at the University of California, San Diego Medical School have provided some of the first empirical evidence that such ripples actually occur in people.
“Think about the experience of stroking a cat. In addition to the shape, location, surroundings, colors, feels, movements, and sounds of the cat, there are emotions and behaviors that you react to. These are all cohesive and overall. It’s tied up, “says senior author Eric Halgren. Professor of Radiology, University of California, San Diego School of Medicine.
“These various aspects of the experience are encoded in places that are distributed throughout the cortical surface of the brain, and the experience is supported by their spatiotemporal firing patterns. The mystery is in these different places. How the activities of the are connected. “
Previous studies, primarily in rodents, have found that hippocampal ripples of different structures organize the regeneration of these spatiotemporal patterns during sleep. This is essential for permanent memory.
A team at the University of California, San Diego, led by Halgren, discovered that ripples occur in all areas of the human cortex, not only during sleep but also during awakening. Ripple was short, lasting about one tenth of a second, and had a consistently narrow frequency close to 90 cycles per second. The authors calculated that a typical short ripple event could contain about 5,000 small modules that are dispersed across the cortical surface and become active at the same time.
This work is part of a doctoral dissertation in neuroscience by lead author Charles W. Dicky.
“Surprisingly, ripples occurred simultaneously and synchronized between all lobes and between both hemispheres, even over long distances,” Dicky said. “Cortical neurons increase firing with ripple rhythms during ripples, potentially supporting interactions between distant locations.
“There was more co-occurrence prior to the success of memory recall, all of which facilitates the integration of various elements that may constitute a particular empirical memory, with dispersed cortical co-occurrence. It suggests that. “
Researchers have found that cortical ripples combine with hippocampal ripples and are often embedded in slower vibrations (1 and 12 cycles per second). These slower rhythms are regulated by cortical activity levels, the central structure that controls the thalamus, and the firing of neurons required for memory integration.
“Since our experience is organized hierarchically in time, so is the rhythm that organizes the cortical activities that produce that experience,” Halgren said.
The study analyzed weekly records taken directly from the brain of 18 patients monitored to determine the cause of an epileptic seizure. Ongoing studies in Halgren’s laboratory show that neuronal firing patterns in different parts of the cortex are more mutually predictable during co-ripping.
“It is impossible to know what its practical meaning is, like other basic researches that deepen our understanding of how the world works,” Halgren said. “But note that schizophrenia, a common and incurable disease, is characterized by mental fragmentation. Our finding and other findings are that certain types of inhibitory interneurons generate ripples. It is important and shows that these cells are known to be selectively present, affected by schizophrenia, as well as high frequency vibrations, probably one aspect of this tragic illness. We’re a little closer to finding a mechanism. “
The co-authors are: IlyaA.Verzhbinsky, Xi Jiang, Burke Q. Rosen, Sophie Kajfez, Jerry J. Shih, Sharona Ben-Haim, all at the University of California, San Diego. Brittany Stederin and Ahmed M. Laslan, Oregon Health & Science University; Emad N. Eskandar, Albert Einstein Medical College; Jorge Gonzalez-Martinez, Cleveland Clinic; and Sydney S. Cash, Harvard University School of Medicine.