Summary: Brain oscillations may help explain how activity of individual neurons links to larger-scale brain networks involved in spatial navigation.
Source: RUB
Spatial navigation is a core cognitive ability that is often impaired in neurological and psychiatric disorders. Research across species has shown that both single neurons and larger neural networks contribute to navigation, but how activity at the cellular level connects with activity at the network level has remained largely unclear.
In a review published in Trends in Cognitive Sciences on 24 May 2019, an international team explored theories that could bridge this gap. The article was co-authored by Dr. Lukas Kunz (University Medical Center Freiburg), Professor Liang Wang (Chinese Academy of Sciences, Beijing), Professor Nikolai Axmacher (Ruhr-Universität Bochum), and collaborators from Columbia University, New York.
The brain’s internal GPS
Decades of animal research have identified specialised neurons that encode spatial information. Place cells in the hippocampus activate when an animal is in a specific location, and grid cells in the entorhinal cortex generate a characteristic patterned representation of space. Together, these cell types form a neural substrate often described as the brain’s “GPS.” In studies with humans, however, researchers typically measure activity from larger-scale networks using methods such as fMRI or scalp EEG, identifying broad brain regions and oscillatory dynamics associated with navigation.
Two independent research teams—one in New York and a collaborative network in Bochum, Freiburg, and Beijing—have proposed a potential link between the single-cell and network perspectives. Their work examines mesoscopic signals, specifically rhythmic oscillations recorded from ensembles of neurons, and how those rhythms might reflect the spatial codes previously observed at the cellular level.
Mesoscopic signals: bridging cells and networks
The groups focused on rhythmic activity in the entorhinal cortex, the region that contains grid cells identified in animal studies. Using intracranial recordings in humans (iEEG) and complementary analyses, they found that characteristics of larger-scale brain oscillations—particularly in the theta frequency band—show patterns analogous to the firing properties of individual spatial cells.
Two broad mechanisms were proposed to explain how oscillations could reflect spatial information. One hypothesis suggests that nearby neurons represent nearby locations, producing a spatially structured pattern across the tissue that would be visible in population-level oscillations. A second hypothesis proposes that navigating in particular directions engages a larger or more diverse set of neurons, and that this increased recruitment produces stronger or distinct oscillatory signatures during movement in those directions.
“Consequently, EEG oscillations may constitute the link between individual cells and the larger-scale networks that are typically investigated in humans,” concludes Axmacher.
Alternative interpretations and next steps
The authors also consider an alternative possibility: the micro-scale and network-scale phenomena might both support spatial behaviour but operate largely independently. As Lukas Kunz notes, “It is just as conceivable that the neural phenomena on the individual-cell scale and the network scale are not linked at all.” Under that view, single-cell firing patterns and mesoscopic oscillations could represent different facets of navigation, each important but not directly causally connected.
To adjudicate between these scenarios, the researchers propose targeted experiments that integrate animal models, human intracranial recordings, and noninvasive measures such as EEG and fMRI. Key goals include determining how mesoscopic oscillations relate to single-unit firing, clarifying which frequency bands (for example, theta) carry spatial representations, and assessing how fMRI signals reflect the same underlying spatial codes.
Understanding these relationships has important clinical implications. If mesoscopic spatial representations reliably reflect single-neuron coding, they could serve as accessible biomarkers for early detection of navigation-related deficits in conditions such as Alzheimer’s disease, epilepsy, and other neuropsychiatric disorders. Conversely, if the scales are affected independently, treatments might need to target micro- and macro-scale dysfunctions separately.
The authors emphasize careful, hypothesis-driven research to integrate findings from animal experiments and human studies. Clarifying whether and how oscillatory activity links single-cell representations to large-scale networks will improve our basic understanding of spatial cognition and may guide future diagnostic and therapeutic approaches.
Source:
RUB
Media Contacts:
Nikolai Axmacher – RUB
Image Source:
The image is in the public domain.
Original Research: Closed access
“Mesoscopic Neural Representations in Spatial Navigation”. Lukas Kunz, Shachar Maidenbaum, Dong Chen, Liang Wang, Joshua Jacobs, Nikolai Axmacher.
Trends in Cognitive Sciences. doi:10.1016/j.tics.2019.04.011
Abstract
Mesoscopic Neural Representations in Spatial Navigation
Neural representations of spatial navigation have mainly been investigated at the microscopic level of single neurons and at the macroscopic level of fMRI. Recent intracranial electroencephalography (iEEG) recordings in patients with epilepsy revealed mesoscopic neural representations of spatial features, including travelled distance, proximity to goals and boundaries, and grid-like hexadirectional orientation. These effects are particularly evident in oscillatory activity within the theta frequency band.
Mesoscopic representations provide a bridge between microscopic single-unit activity and macroscopic imaging signals. The review outlines experimentally testable scenarios linking mesoscopic oscillations to single-neuron firing, other neural rhythms, and fMRI responses. Ultimately, neural spatial representations at this mesoscopic scale could offer new biomarkers for neurological and psychiatric diseases that affect navigation and memory.