Understanding behavior requires measuring how many brain regions interact at the same time. Yet most optical techniques historically faced a trade-off: they could record neural activity with good cellular or regional specificity, but only from a limited number of sites. This made it difficult to follow how distributed brain circuits coordinate activity during behavior.
In this Nature Methods paper, new team member Yaroslav Sych together with Fritjof Helmchen and other colleagues at University of Zurich, introduced high-density multi-fiber photometry: a compact, chronically implantable optical recording approach designed to monitor calcium activity simultaneously across many brain regions in mice. By combining arrays of optical fibers with genetically encoded calcium indicators, the method makes it possible to track large-scale circuit dynamics while preserving the advantages of optical readout: cell-type specificity, chronic recordings, and compatibility with behavioral experiments.
A major advance of the study is scale. The authors demonstrated simultaneous calcium recordings from up to 48 brain regions, including cortical, hippocampal, thalamic and striatal areas, during behavior. This allowed them to move beyond isolated regional signals and observe how activity patterns unfold across distributed networks during tasks such as texture discrimination.
The method is not limited to observation. The authors also showed that multi-fiber photometry can be combined with multi-site optogenetic perturbations, allowing selected brain regions to be stimulated while network-wide calcium responses are recorded. In proof-of-concept experiments, perturbing ventral thalamic nuclei produced distributed network effects and behavioral deficits, illustrating how the approach can link causal circuit manipulation to large-scale brain dynamics.
This work provides an important technical bridge between local circuit neuroscience and whole-brain systems neuroscience. It does not offer single-cell resolution like two-photon microscopy, nor whole-brain coverage like fMRI. Instead, it occupies a powerful intermediate level: mesoscale, multi-region, optically defined recordings in behaving animals.
A useful way to summarize the contribution is: high-density multi-fiber photometry makes it possible to follow the “conversation” between many brain areas at once, and to perturb parts of that conversation to test how they shape behavior.
By enabling chronic, simultaneous recordings across distributed circuits, this method opened new possibilities for studying how brain-wide dynamics support perception, decision-making, movement, and internal states. It is a particularly valuable tool for questions in which the key phenomenon is not located in one region alone, but in the coordinated activity of networks.
To know more:
- Sych, Y., Chernysheva, M., Sumanovski, L. T., & Helmchen, F. (2019). High-density multi-fiber photometry for studying large-scale brain circuit dynamics. Nature Methods, 16, 553–560. https://doi.org/10.1038/s41592-019-0400-4.