Brain ripples may help bind information across the human cortex: Ubiquitous bursts of brain waves appear to synchronize disparate and distant elements of memory, unifying them upon recollection

A fundamental mystery of the human cortex is how its 16 billion neurons integrate or bind the many different kinds of information they encode into a single coherent unified experience or memory.

Scientists have hypothesized that such binding involves high-frequency oscillations or “ripples” that promote neural interactions, much like rhythm does in music or dance. In a paper published July 7, 2022 in PNAS, researchers at University of California San Diego School of Medicine provide some of the first empirical evidence that such ripples do, in fact, occur in people.

“Think about the experience of petting your cat: its form, location, surroundings, color, feel, movement and sound, plus your own responding emotions and actions. They are all bound together in a coherent whole,” said senior author Eric Halgren, PhD, professor of radiology at UC San Diego School of Medicine.

“These different aspects of the experience are encoded in locations distributed across the cortical surface of the brain, and the experience is sub-served by their spatiotemporal firing pattern. The mystery has been how activities in those different locations get connected.”

Previous studies, mainly in rodents, had found that ripples in a different structure, the hippocampus, organize the replay of these spatiotemporal patterns during sleep, and this is essential for making memories permanent.

The UC San Diego team, led by Halgren, found that ripples also occur in all areas of the human cortex, in waking as well as sleep. The ripples were brief, lasting roughly one-tenth of a second, and had a consistent narrow frequency close to 90 cycles per second. The authors calculated that a typical brief ripple event may involve approximately 5,000 small modules becoming active simultaneously, distributed across the cortical surface.

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