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- Optomapping: A breakthrough method for exploring synaptic connections in the brain
Pioneering technique developed by researchers at The Institute offers new insights into how neurons communicate
SOURCE: The Research Institute of the McGill University Health Centre (The Institute)
January 30, 2025
Scientists at The Research Institute of the McGill University Health Centre (The Institute) have implemented a groundbreaking method called “optomapping,” which dramatically accelerates the study of neurons in the brain. Led by Jesper Sjöström, PhD, and published in The Innovation, this new work provides unprecedented insights into how neurons connect and communicate, offering hope for better understanding neurological disorders such as epilepsy and autism.
Gathering speed in understanding neurons
The human brain contains an estimated 100 trillion synapses—microscopic connections through which neurons communicate. Studying these connections has long been a challenge, as traditional methods using miniature electrodes are time-intensive and can identify just a few neuronal connections in a day. Optomapping revolutionizes this process.

“With optomapping, we can map hundreds of neurons and reveal dozens of connections in just an hour,” explains Prof. Sjöström, who is a scientist in the Brain Repair and Integrative Neuroscience (BRaIN) Program at The Institute. “This represents a massive increase in throughput and allows us to explore much larger brain areas than ever before.”
The research team tested over 30,000 candidate connections and characterized approximately 1,800 synapses in the visual cortex of a mouse brain. Their findings revealed new insights into how the brain’s communication networks are organized, such as the distinct ways different types of inhibitory neurons connect to other cells, and how the strength of these connections changes depending on the layers of the brain’s cortex.
Applications for neurological disorders
In this publication, the researchers shared three key discoveries made using optomapping. First, they found unique connection patterns onto different types of inhibitory neurons, challenging the traditional understanding of how information flows in the brain’s cortical layers. Second, they showed that the brain’s communication patterns are carefully balanced, with some connections amplifying signals (excitation) and others calming them (inhibition). Finally, they observed an imbalance in how different neuron types are activated, with inhibition consistently tempering excitation—a finding that could help explain brain function in both health and disease.
“Conditions like autism and epilepsy often involve imbalances between excitatory and inhibitory neurons,” says Christina Chou, PhD, a postdoctoral fellow in the Sjöström lab and first author of the paper. “Optomapping gives us the tools to pinpoint these changes, which could lead to more targeted and effective treatments. For instance, by identifying specific connectivity imbalances in autism, optomapping could help researchers design therapies that restore the brain’s natural communication patterns.”
Collaboration and impact
The project was made possible through the cutting-edge technology and expertise provided by The Institute’s Molecular Imaging Platform, where high-resolution 3D images of neurons were captured and analyzed. The platform’s advanced imaging capabilities allowed the team to visualize and analyze neuronal arbors with unprecedented clarity.
The study received funding from multiple sources, including the Montreal General Hospital Foundation, the Canadian Institutes of Health Research (CIHR), and the Fonds de recherche du Québec (FRQ) as well as fellowship support for team members from institutions such as the Natural Sciences and Engineering Research Council of Canada (NSERC) and McGill University.
Looking ahead, the team plans to use optomapping to study how connectivity patterns are altered in neurodevelopmental disorders such as Fragile X syndrome. This genetic condition, linked to an elevated risk of epileptic seizures, strongly affects synapses, and thus is a prime candidate for study using the new method’s high-throughput capabilities. The researchers aim to accelerate discoveries in neuroscience and bring the promise of precision medicine closer to reality.
About the publication:
Principles of visual cortex excitatory microcircuit organization. Christina Y.C. Chou, Hovy H.W. Wong, Connie Guo, Kiminou E. Boukoulou, Cleo Huang, Javid Jannat, Tal Klimenko, Vivian Y. Li, Tasha A. Liang, Vivian C. Wu, P. Jesper Sjöström. The Innovation, Volume 6, Issue 1, 100735
DOI: https://doi.org/10.1101/2023.12.30.573666
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