Human subcortical pathways automatically detect collision trajectory without attention and awareness

Abstract

Detecting imminent collisions is essential for our survival and is likely supported by evolutionarily conserved mechanisms in the brain. Using high-resolution 7T fMRI, we investigated subcortical pathways for detecting collision trajectories in healthy human subjects and hemianopic patients. When healthy participants focused their attention on a central fixation task, their superior colliculus (SC), ventromedial pulvinar (vmPul) and ventral tegmental area (VTA) elicited stronger responses to a peripheral object approaching on head-collision courses compared to near-miss trajectories. Correlation and path analyses of collision-sensitive responses revealed collision sensitivity in the SC-vmPul and SC-VTA pathways without attention and cortical influence. Both behavioral performance and SC responses showed higher sensitivity to looming stimuli from the upper visual field. For hemianopic patients with unilateral lesions of the geniculostriate pathway, the ipsilesional SC, vmPul and VTA showed collision sensitivity to looming stimuli in their blind visual field, in the absence of their awareness. Stronger responses in the SC were also associated with better detection performance of the collision events. These findings clearly demonstrate that human tectofugal pathways, without attention and awareness, automatically detects approaching objects on a collision course, supporting blindsight to impending visual threats.