Causal mapping of a midbrain circuit supporting 3-D vision in humans and monkeys

Abstract Frontal-eyed species use a combination of conjugate and vergence eye movements, termed 3-D gaze, to scan their environment¹–³. The neural circuits mediating conjugate gaze have been extensively characterized, but those governing vergence remain disproportionately obscure⁴. Here, we combine lesion and deep brain stimulation data from 67 humans and 19 monkeys to causally link vergence function to a midbrain region rostral to the superior colliculus, encompassing the nucleus of the posterior commissure (NPC), and aligning with the location of neurons whose activity correlates with vergence in monkeys⁵,⁶. Cross-species eye movement analysis suggests the NPC region houses a vergence integrator maintaining stable eye alignment in depth⁵,⁷,⁸. Multimodal connectivity revealed NPC connections to the pretectum and the supraoculomotor area, brain regions previously linked to visual maps of 3-D space and premotor control of the near response, enabling focus across varying viewing distances⁹. Collectively, these results suggest the NPC region is a key node for 3-D visuomotor transformations. These findings bridge a translational gap between physiological observations in monkeys and clinical disorders in humans, revealing a subcortical circuit for 3-D vision.