Summary: New experiments reveal how the brain’s internal compass adapts to changing environments and how those navigation processes can break down in conditions such as Alzheimer’s disease.
Source: McGill University
Researchers have made significant progress in understanding the brain circuitry that provides our sense of direction by recording neural activity with state-of-the-art imaging and analysis methods.
The study illuminates how the brain reorients itself when environmental cues shift, and it highlights mechanisms that may fail in degenerative conditions that cause disorientation and spatial confusion.
“The past decade has brought a technological revolution in neuroscience, enabling questions that were once out of reach,” says Mark Brandon, Associate Professor of Psychiatry at McGill University and a researcher at the Douglas Research Centre. He co-led the work with Zaki Ajabi, formerly a student at McGill and now a postdoctoral fellow at Harvard University.
Reading the brain’s internal compass
To investigate how visual cues influence the brain’s internal compass, the team exposed mice to a controlled but disorienting virtual environment while recording neural activity. Using the latest neuronal recording techniques, they decoded head-direction signals with unprecedented precision.
This high-resolution readout of the animals’ internal heading made it possible to examine how Head-Direction (HD) cells—the neurons that form the brain’s compass—support reorientation when surroundings change or become ambiguous.
The researchers identified a dynamic property of the HD network they call “network gain.” Network gain reflects a second, previously underappreciated dimension of population activity that becomes especially prominent when visual cues conflict or are uncertain. Changes along this dimension predicted how the neural compass realigned and the speed of that realignment after disorientation.
“It appears the brain can implement a kind of reset mechanism that rapidly reorients its internal compass in confusing situations,” Ajabi explains.
Although the visual situations used in the experiments were artificial, the authors note these scenarios are increasingly relevant to humans, given the widespread use of virtual reality and other immersive technologies. The findings may help explain how virtual environments can override or distort our natural sense of direction.
Inspired by the recordings, the team developed computational models to formalize how population-level dynamics produce flexible, reliable heading representations. The models integrate the newly identified gain dimension with classic descriptions of HD circuitry to explain reorientation, drift, and recalibration when cues change.
“This study is a clear example of how combining precise experimental recordings with computational modeling advances our understanding of the neural activity that drives behavior,” says Xue-Xin Wei, a computational neuroscientist and Assistant Professor at The University of Texas at Austin, who is a co-author on the paper.
Implications for degenerative disease
The results carry important implications for Alzheimer’s disease and related disorders. Brandon notes that early in Alzheimer’s many people report getting lost or disoriented even in familiar places. By revealing how the HD network anchors to visual cues, retains recent cue information, and recalibrates after sustained changes, these findings may point to biomarkers or behavioral assays for earlier detection.
A more complete picture of how the brain’s navigation system operates could also improve how clinicians evaluate treatments aimed at preserving or restoring spatial orientation in neurodegenerative disease.
About the study
Funding: Supported by the Natural Sciences and Engineering Research Council of Canada and the Canadian Institutes of Health Research.
About this neuroscience research news
Author: Shirley Cardenas
Source: McGill University
Contact: Shirley Cardenas – McGill University
Image: The image is in the public domain
Original Research: Open access. “Population dynamics of head-direction neurons during drift and reorientation” by Mark Brandon et al. Nature
Abstract
Population dynamics of head-direction neurons during drift and reorientation
The head-direction (HD) system functions as the brain’s internal compass and has often been modeled as a one-dimensional ring attractor. Unlike a magnetic compass that refers to global poles, the HD system anchors to local environmental cues, maintaining a stable offset when those cues rotate and drifting when external references are absent.
Key questions remain about the mechanisms that support anchoring and drift, and these are best addressed by examining population activity. In particular, it is unclear whether a one-dimensional description of population dynamics suffices under conditions of reorientation and cue conflict.
In this study, the authors performed population recordings of thalamic HD cells using calcium imaging while they rotated a salient visual landmark. Across experiments, activity varied along a second dimension—network gain—which became especially important during cue conflict and ambiguity. Variations in network gain predicted realignment and drift dynamics, including the speed of realignment.
In darkness, network gain retained a memory trace of the previously visible landmark. Additional experiments showed that after brief exposures to a rotated cue the HD network returned to its baseline orientation, whereas longer exposures produced more persistent changes. This dependence on prior experience indicates that memories of associations between HD neurons and external cues influence the internal representation of heading.
Continuous rotation of a visual landmark induced a corresponding rotation in the HD representation that persisted in darkness, demonstrating experience-dependent recalibration of the HD system. The authors present a computational model that formalizes how the neural compass flexibly adapts to changing cues to maintain a reliable heading representation.
Taken together, these results challenge classical one-dimensional accounts of the HD system and provide new insight into how internal compass signals interact with the cues to which they anchor.