Summary: Theta oscillations help the brain remember the locations a person is attempting to reach during navigation.
Source: RUB
Researchers report new insights into how specific brain rhythms support navigation, with potential future applications for patients with neurodegenerative disorders.
The brain appears to implement an internal navigation system that functions much like a biological GPS, but many details of how it operates remain unclear. In the journal Science Advances, researchers from Freiburg, Bochum, and Beijing present evidence that rhythmic fluctuations in brain activity known as theta oscillations contribute to spatial navigation by organizing how location-specific memories are reactivated. Their conclusions come from recordings of neuronal activity in epilepsy patients who had intracranial electrodes implanted for clinical planning. During a virtual reality navigation task, the implanted electrodes captured the brain’s electrical signals while participants learned and recalled object-location associations.
A research team led by Dr. Lukas Kunz at Universitätsklinikum Freiburg and Professor Nikolai Axmacher, Head of the Department of Neuropsychology at Ruhr-Universität Bochum, published these findings on 3 July 2019.
Experiments in virtual reality
Previous studies have shown that brain oscillations follow characteristic patterns during navigation. In particular, theta oscillations—rhythmic activity around four hertz—have been implicated in spatial orientation and memory. However, the precise mechanism by which theta rhythms support navigation and the separation of competing spatial memories was not fully understood.
In this study, epilepsy patients learned to associate specific objects with distinct locations inside a virtual environment. For each object-location pair, the researchers identified a unique pattern of large-scale electrophysiological activity. Later, when participants were asked to navigate back to a cued location, the brain reinstated those specific activity patterns as the person moved through the virtual space.
Importantly, the reactivation of different object-location representations was organized at distinct moments within the hippocampal theta cycle. In other words, the brain did not replay all remembered locations at once but sequenced them across different theta phases. “Accordingly, theta oscillations may coordinate the reactivation of different memories and help distinguish between competing memories,” explains Lukas Kunz. The timing of reactivation relative to the theta cycle appeared to be behaviorally meaningful: when representations locked to more distinct theta phases, participants showed better memory performance for the cued location.
Implications for Alzheimer’s and other disorders
Disorientation and spatial memory loss are prominent symptoms in many neurological disorders, including Alzheimer’s disease. Understanding the neural mechanisms that support goal-directed navigation is therefore important for both basic neuroscience and clinical research. “Many disorders are associated with disorientation and memory loss; it is therefore vitally important to gain an understanding of the underlying neuronal mechanisms,” says Nikolai Axmacher. The researchers hope that the theta phase-coding mechanism they identified could eventually contribute to biomarker development for neurodegenerative conditions or inform therapeutic strategies aimed at improving spatial memory.
Funding
This work was supported by multiple funding agencies, including the German Federal Ministry of Education and Research (grant no. 01GQ1705A), the German Research Foundation (EXC 1086, SFB 1280, SFB 874), the German Federal Ministry for Economic Affairs and Energy, the Faculty of Medicine at Freiburg University, the Epilepsie-Akademie Berlin-Bethel of the v. Bodelschwingh Foundation Bethel in Bielefeld, the National Science Foundation (BCS-1724243), the National Institutes of Health (563386), the Chinese Academy of Science (XDB32010300), the Beijing Municipal Science and Technology Commission (Z171100000117014), the Natural Science Foundation of China (31771255), and the Else Kröner-Fresenius-Stiftung.
Source:
RUB
Media contacts:
Dr. Lukas Kunz – RUB
Image source:
Image credit: RUB, Marquard.
Original research (open access):
“Hippocampal theta phases organize the reactivation of large-scale electrophysiological representations during goal-directed navigation” by Lukas Kunz et al., published in Science Advances. DOI: 10.1126/sciadv.aav8192
Abstract (summary)
The study reports that humans can maintain and follow multiple spatial goals and that hippocampal theta phases organize the dynamic reactivation of large-scale electrophysiological representations corresponding to object cues. During goal-directed navigation in a virtual environment, reactivation of different cue representations occurred at stimulus-specific theta phases. Greater separation of these representations across theta phases predicted superior memory performance. These findings support a shared neural mechanism between working memory and goal-directed navigation and provide new insight into the functional role of the hippocampal theta rhythm.