An implanted lennula approach to measure neural Ca²⁺ responses in the awake marmoset visual cortex

We present a novel approach for endoscopic calcium imaging in the marmoset extrastriate visual cortex, combining a chronically implanted microprism lens with an integrated injection cannula. This method achieved stable, longitudinal imaging of visually responsive GCaMP-expressing neurons over multiple weeks. Using a head-mounted miniscope in two subjects, we repeatedly presented naturalistic visual stimuli and longitudinally tracked the activity of more than one hundred neurons across sessions within an 800-μm² field of view. Stably monitored neurons in cortical areas V3 and MT responded reliably to visual images and movies over periods up to 3 weeks. Cells having different visual response preferences were spatially intermixed. These results demonstrate the feasibility of longitudinal calcium imaging in the primate visual cortex using a single-surgery, integrated lens-cannula approach, and provide initial insights into single neuron response stability and diversity to naturalistic stimuli in mid-level cortical visual areas.