Researchers at the University of California San Diego School of Medicine provide some of the first experimental evidence that such ripples do in fact occur in humans.
“Think about the experience of petting your cat: shape, position, surroundings, color, feel, movement and sound, plus emotions and cues,” says senior author Eric Halgren. act on your own response. , PhD, professor of radiology at UC San Diego School of Medicine.
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“These different aspects of experience are encoded in locations distributed on the cortical surface, and the experience is served by their spatial firing pattern. The mystery is how the activities work at these locations. Those disparate locations are interconnected.”
Previous studies, mainly in rodents, have found that ripples in another structure, the hippocampus, organize the playback of these spatial patterns during sleep, and this is needed to create permanent memories.
The UC San Diego team, led by Halgren, found that ripples also appear in all areas of the human cerebral cortex, during wakefulness and sleep. The ripples are short, lasting about 1/10th of a second, and have a consistently narrow frequency of nearly 90 cycles per second. The authors calculated that a typical short ripple event might involve about 5,000 small modules becoming active simultaneously, distributed across the cortical surface.
This work is part of first author Charles W. Dickey’s doctoral thesis in neuroscience.
“Remarkably, the ripples co-occur and are synchronous across all lobes and between both hemispheres, even at great distances,” says Dickey. “The cortical neurons fire when rippling, in rhythm with the ripple, capable of supporting interactions between distant sites.
“More co-occurrence precedes successful memory recall. All show that uniformly distributed, cortical ripples promote the integration of disparate elements that can form a single memory. specific experience.”
The researchers found that Cortical ripples are often associated with hippocampal ripples and are embedded in slower oscillations (1 and 12 cycles per second). These slower rhythms are regulated by a central structure that controls cortical and thalamic activity levels and regulates neuronal activation, which is necessary for memory consolidation.
“Since our experiences are hierarchically ordered in time, so is the rhythm that organizes our cortical activities that produce that experience,” Halgren said.
The study involved the analysis of week-long audio recordings taken directly from inside the brains of 18 patients being monitored to determine the source of their epileptic seizures. Ongoing work in Halgren’s lab demonstrates that patterns of neuronal activation in different parts of the cerebral cortex are more predictive of each other during co-ripple and synchrony. ripples have to do with linking letters into words and meaning with action.
“Like any other fundamental research aimed at improving our understanding of how the world works, we don’t know what it actually means,” Halgren said.
“But I would like to note that schizophrenia, a common and incurable disease, is characterized by mental fragmentation. Our findings and those of others indicate a type of interneuron. specific inhibition is important for the generation of ripples.These cells are known to selectively affect schizophrenia as well as high-frequency oscillation.Perhaps we are closer. a little bit to finding the mechanism for one aspect of this tragic disease.”
Source: Eurekalert
