Thanks for the support from the NEI intramural program

8. This work was a collaborative effort between
Dr.Okihide Hikosaka’s lab, Dr.Hendrikje Nienberg(NEI), @nienborglab.bsky.social
Dr. Ken-ichi Inoue & Masahiko Takada (Kyoto University)
Dr.Marc Sommer’s lab (Duke University) @neurocircuits.bsky.social @dukebrain.bsky.social

In summary, our study: (1)Resolves a long-standing debate on cortical–subcortical communication. (2)Demonstrates the power of retrograde optogenetics for behavioral control and pathway-specific tagging. (3)Provides a framework for studying perception–action transformations in primate brains

6. FEF-recipient SC neurons were strongly biased toward motor-related signals. This supports a visuomotor convergence model: Diverse cortical signals converge onto motor-selective neurons in the SC, where saccade commands are generated.

5. Do these diverse cortical signals remain separate in the SC — or converge? To answer this, we stimulated FEF while recording from SC, identifying SC neurons that directly receive the FEF output.

4 Characterizing these SC-projecting FEF neurons revealed a diverge population: visual, visuo-movement, movement. This diversity rules out a purely motor-dominant output from the FEF.

3.Because the virus is transported from axon terminals back to the soma, we could optically tag FEF neurons that specifically project to SC. Neurons with short response latencies (<5ms) were identified as directly activated projection neurons.

2. Optical activation of SC-projecting FEF neurons (1) Evoked robust contralateral saccades (2) Shortened or prolonged saccade reaction times, depending on direction. This demonstrates powerful causal control of behavior using retrograde optogenetics in primates.

1.To directly test these models, we leveraged retrograde optogenetics, to dissect a projection-defined circuit in awake macaques. We inject a retrograde viral vector into the SC and optically stimulated the FEF, selectively activating the FEF-SC pathway with high specificity.

-> Pure motor commands (motor-dominant)?
->Mixed visual & motor signals that converge downstream? (visuomotor convergence)
->Or mixed signals preserved all the way into subcortical circuits (no convergence)?
This has been debated for decades.

Every time your eyes scan a scene, visual input must be converted into a saccade vector that guides eye movements. But what exactly is sent from cortex to subcortex during this transformation?

-> Pure motor commands (motor-dominant)?
->Mixed visual & motor signals that converge downstream? (visuomotor convergence)
->Or mixed signals preserved all the way into subcortical circuits (no convergence)?
This has been debated for decades.