Loss and enhancement of layer-selective signals in geniculostriate and corticotectal pathways of adult human amblyopia.

How abnormal visual experiences early in life influence human subcortical pathways is poorly understood. Using high-resolution fMRI and pathway-selective visual stimuli, we investigate the influence of amblyopia on response properties and the effective connectivity of subcortical visual pathways of the adult human brain. Compared to the normal and fellow eyes, stimuli presented to the amblyopic eye show selectively reduced response in the parvocellular layers of the lateral geniculate nucleus and weaker effective connectivity to V1. Compared to the normal eye, the response of the amblyopic eye to chromatic stimulus decreases in the superficial layers of the superior colliculus, while response of the fellow eye robustly increases in the deep SC with stronger connectivity from the visual cortex. Therefore, amblyopia leads to selective parvocellular alterations of the geniculostriate and corticotectal pathways. These findings provide the neural basis for amblyopic deficits in visual acuity, ocular motor control, and attention.