Summary: Scientists have made a new discovery regarding rhythmic brain signals known as theta oscillations.
These neural dances, primarily observed in the hippocampus, were previously thought to be driven mostly by external events. However, the study revealed that memory recall actually incites more of these oscillations than real-time experiences.
This research has implications for new therapeutic strategies in conditions that affect memory, such as seizures, strokes and Parkinson’s disease.
- The study found that theta oscillations, rhythmic brain signals, are more prevalent when a person is remembering events rather than experiencing them.
- The research suggests that memory could be harnessed to stimulate these oscillations in the brain, potentially leading to memory improvements in patients with cognitive impairments.
- The results were derived from a unique virtual reality experiment involving epilepsy patients, providing an innovative approach to understanding the neural basis of memory.
Source: University of Arizona
Neurons produce rhythmic patterns of electrical activity in the brain. One of the unresolved questions in neuroscience is what primarily drives these rhythmic signals, called oscillations.
Researchers from the University of Arizona have found that simply remembering events can trigger them, even more so than when people experience the actual event.
The researchers, whose results are published in the journal Neuron, specifically focused on what are known as theta oscillations, which occur in the hippocampus region of the brain during activities such as exploration, navigation and sleep. The hippocampus plays a crucial role in the brain’s ability to remember the past.
Prior to this study, the external environment was thought to play a more important role in driving theta oscillations, said Arne Ekstrom, professor of cognition and neural systems in the UArizona Department of Psychology and senior author of the study. But Ekstrom and his collaborators found that memory generated in the brain is the main driver of theta activity.
“Surprisingly, we found that in humans, theta oscillations are more prevalent when someone is just remembering things compared to directly experiencing events,” said lead study author Sarah Seger, a graduate student in the Department of Neuroscience.
The results of the study could have implications for treating patients with brain damage and cognitive impairments, including patients who have experienced seizures, strokes and Parkinson’s disease, Ekstrom said. Memory could be used to create stimulations from within the brain and drive theta oscillations, potentially leading to 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 monitored at the center in preparation for epilepsy surgery. As part of the monitoring, electrodes were implanted into the patients’ brains to detect occasional seizures. The researchers recorded the theta oscillations in the brain’s hippocampus.
Patients participated in a virtual reality experiment in which they were given a joystick to navigate to shops in a virtual city on a computer. When they arrived at the correct destination, the virtual reality experiment was paused.
The researchers asked the participants to imagine the place where they started their navigation and instructed them to mentally navigate the route they just passed through. The researchers then compared theta oscillations during the initial navigation with the participants’ subsequent recollection of the route.
During the actual navigation process using the joystick, the oscillations were less frequent and shorter in duration compared to oscillations that occurred when the participants were just imagining the route. So the researchers conclude that memory is a strong driver of theta oscillations in humans.
One way to compensate for decreased cognitive function is by using cognitive training and rehabilitation, Ekstrom said.
“Basically, you take a patient who has memory impairments and you try to teach them to be better at remembering,” he said.
In the future, Ekstrom plans to conduct this research in ambulatory patients, as opposed to bedridden patients, and observe how free navigation compares to memory in terms of brain oscillations.
“Being able to directly compare the oscillations present during the original experience and during a later retrieval of it is a major step forward in the field in terms of designing new experiments and understanding the neural basis of memory ,” Seger said.
About this memory research news
Original research: Closed access.
“Memory-related processing is the primary driver of human hippocampal theta oscillations” by Sarah E. Seger et al. Neuron
Memory-related processing is the primary driver of human hippocampal theta oscillations
- The 3-12 Hz hippocampal “theta” oscillation in rodents is related to locomotion and associated with navigation
- Yet, theta oscillations are also observed in humans during verbal memory processing
- Here we tested whether navigation or memory was the primary driver of human theta
- The results showed greater occurrence of human hippocampal theta during memory
Decades of work in rodents suggest that movement is a strong driver of hippocampal low-frequency “theta” oscillations. Confusingly, such movement-related theta increases in primates are less persistent and of lower frequency, leading to questions about their functional relevance.
Verbal memory encoding and retrieval lead to robust increases in low-frequency oscillations in humans, and one possibility is that memory may be a stronger driver of hippocampal theta oscillations in humans than navigation.
Here, neurosurgical patients navigated routes and immediately mentally simulated the same routes while undergoing intracranial recordings.
We found that mentally simulating the same route just navigated elicited oscillations that were of greater force, higher frequency, and longer duration than those involving navigation.
Our results suggest that memory is a more potent driver of human hippocampal theta oscillations than navigation, supporting models of internally generated theta oscillations in the human hippocampus.