Multiplexed mapping of long-range projections with FluoCode, a combinatorial fluorescent barcoding system

FluoCode multiplexes long-range projection mapping within single mice and marmosets, using AAV color barcodes to resolve topographic maps across up to 21 cortical areas.

• Why it matters: Conventional viral tracing labels only one or a few pathways per animal, and whole-brain atlas registration across individuals is limited by variability in morphology and wiring.
• What they did: The system uses AAV vectors expressing two of seven fluorescent proteins to generate 21 distinct color codes, plus a FluoCode Reader that classifies neurite signals by color combinations and morphology.
• The result: In individual mice, projections from up to 21 cortical areas were mapped to subcortical regions, and in marmosets primary visual cortex mapping revealed topographic projections in higher visual areas and thalamic nuclei.

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