Human study provides evidence that theta phase precession promotes memory formation and retrieval

Previous research in neuroscience has identified numerous neural processes by which the human brain forms, stores, and retrieves important information, such as domain-specific knowledge and memories. One of the dimensions of human memory is the ability to relate various aspects of experience to specific life events.

Previous studies have suggested that this memory-related process is supported by phase precession, which corresponds to a change in the timing at which specific neurons are activated. But until now, this hypothesis has not been confirmed experimentally.

Researchers from the University of California, Davis, Harvard Medical School, Toronto Western Hospital, and Cedars-Sinai Medical Center recently conducted a study to probe the relationship between phase precession and memory.

Their findings, published in Human behaviorsuggest that theta phase precession, the change in the timing at which specific neurons fire relative to the theta rhythm in the brain, contributes to memory formation and retrieval.

“Our study was inspired by previous work showing that the relative timing of spikes versus population activity in the form of field potentials changes dynamically as animals navigate an environment,” said Jie Zheng, first author of the article, at Medical Xpress.

“In extending this idea to human memory, the primary goal was to test the functional role of such dynamic timing signals during episodic memory formation and retrieval of complex event sequences in a natural, non-natural task. space.”

Zheng and colleagues recruited 22 study participants and recorded single-neuron activity and local field potentials in their medial temporal lobe while they encoded and retrieved memories of video clips. The team incorporated event boundaries (i.e., contextual changes) into the video clips because this allowed them to mimic the process by which humans form memories in their daily lives.

The researchers then asked the participants to remember the events they observed in the film clips and the order in which they occurred. They then analyzed the activity of a single neuron that they recorded while the participants watched the video clips and recalled the memory of the viewed clips.

“The study was conducted in patients with pharmacologically resistant epilepsy, where we were able to simultaneously record the activity of individual neurons as well as population field potential signals,” Zheng said. “We observed that the precise time at which neurons fired was linked to ongoing theta rhythms in the brain and that this relative timing changed dynamically (called phase precession).”

The experiments carried out by Zheng and his colleagues produced very interesting results. The team observed dynamic phase precession in participants’ brains throughout the experiment, with specific neurons changing the timing with which they fired at different stages of the experimental task.

“We found strong theta phase precession at the event boundaries when participants were watching the clips and also when they were answering memory questions,” Zheng said. “The strength of theta phase precession was also predictive of participants’ memory accuracy, particularly for their order memory.”

Overall, the results of this recent study support the role of theta phase procession in the formation and retrieval of episodic memories. In the future, they could pave the way for other studies exploring the link between phase precession and specific memory processes.

“We would like to study the mechanisms underlying memory formation and retrieval of dynamic experiences with different sensory inputs (e.g., visual and auditory), how the order of events is encoded, and how phase precession Theta supports these consolidation and recovery processes,” Zheng added.

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