A scalable, all-optical method for mapping synaptic connectivity with cell-type specificity.

Area of Science:

• Neuroscience
• Molecular Biology
• Genetics

Background:

• Single-cell transcriptomics reveals extensive cell-type heterogeneity in the mammalian brain.
• Mapping cell-type-specific neural circuit connectivity remains a significant challenge due to low-throughput methods.
• Advances in optical tools (e.g., genetically encoded voltage indicators) and spatial transcriptomics offer new possibilities for high-throughput circuit analysis.

Purpose of the Study:

• To develop and apply a high-throughput, optically-based method for assaying long-range synaptic connectivity with cell-type specificity.
• To investigate cell-type-specific synaptic innervation patterns of thalamic and contralateral inputs onto motor cortical neurons.
• To overcome the limitations of low-throughput recording approaches in characterizing detailed circuit connectivity.

Main Methods:

• Utilized advanced optical tools, including genetically encoded voltage indicators, for perturbing and observing neural circuit activity.
• Integrated spatial transcriptomics for *in situ* cell-type identification based on gene expression signatures.
• Applied the combined optical and transcriptomic approach to map synaptic connectivity onto over 1000 motor cortical neurons.

Main Results:

• Demonstrated a high-sensitivity, high-throughput optical method for mapping long-range synaptic connectivity.
• Revealed cell-type-specific synaptic innervation patterns in the motor cortex.
• Found that neurons within the same cortical layer receive distinct levels of synaptic input, a resolution not achievable with previous methods.

Conclusions:

• The developed optical approach significantly enhances the throughput and specificity of neural circuit mapping.
• This method uncovers fine-grained differences in synaptic input even among neurons in the same cortical layer.
• Provides a powerful new tool for understanding the complex circuitry of the mammalian brain at cellular resolution.