Neurons produce rhythmic patterns of electrical activity within the brain. One among the unsettled questions in the sector of neuroscience is what primarily drives these rhythmic signals, called oscillations. University of Arizona researchers have found that simply remembering events can trigger them, much more so than when individuals are experiencing the actual event.

The researchers, whose findings are published within the journal Neuron, specifically focused on what are referred to as theta oscillations, which emerge within the brain’s hippocampus region during activities like exploration, navigation and sleep. The hippocampus plays a vital role within the brain’s ability to recollect the past.

Prior to this study, it was believed that the external environment played a more necessary role in driving theta oscillations, said Arne Ekstrom, professor of cognition and neural systems within the UArizona Department of Psychology and senior creator of the study. But Ekstrom and his collaborators found that memory generated within the brain is the foremost driver of theta activity.

“Surprisingly, we found that theta oscillations in humans are more prevalent when someone is just remembering things, in comparison with experiencing events directly,” said lead study creator Sarah Seger, a graduate student within the Department of Neuroscience.

The outcomes of the study could have implications for treating patients with brain damage and cognitive impairments, including patients who’ve experienced seizures, stroke and Parkinson’s disease, Ekstrom said. Memory may very well be used to create stimulations from inside the brain and drive theta oscillations, which could potentially result in improvements in memory over time, he said.

UArizona researchers collaborated on the study with researchers from the University of Texas Southwestern Medical Center in Dallas, including neurosurgeon Dr. Brad Lega and research technician Jennifer Kriegel. The researchers recruited 13 patients who were being monitored at the middle in preparation for epilepsy surgery. As a part of the monitoring, electrodes were implanted within the patients’ brains for detecting occasional seizures. The researchers recorded the theta oscillations within the hippocampus of the brain.

The patients participated in a virtual reality experiment, wherein they got a joystick to navigate to shops in a virtual city on a pc. Once they arrived at the right destination, the virtual reality experiment was paused. The researchers asked the participants to assume the placement at which they began their navigation and instructed them to mentally navigate the route they only passed through. The researchers then compared theta oscillations during initial navigation to participants’ subsequent recollection of the route.

In the course of the actual navigation process using the joystick, the oscillations were less frequent and shorter in duration in comparison with oscillations that occurred when participants were just imagining the route. So, the researchers conclude that memory is a robust driver of theta oscillations in humans.

One option to compensate for impaired cognitive function is through the use of cognitive training and rehabilitation, Ekstrom said.

“Principally, you’re taking a patient who has memory impairments, and you are trying to show them to be higher at memory,” he said.

In the longer term, Ekstrom is planning to conduct this research in freely walking patients versus patients in beds and find how freely navigating compares to memory with regard to brain oscillations.

“With the ability to directly compare the oscillations that were present through the original experience, and through a later retrieval of that may be a huge step forward in the sector when it comes to designing latest experiments and understanding the neural basis of memory,” Seger said.