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Visual fMRI Responses in Human Superior Colliculus Show a Temporal–Nasal Asymmetry That Is Absent in Lateral Geniculate and Visual Cortex

¹Wellcome Department of Imaging Neuroscience, Institute of Neurology and ²UCL Institute of Cognitive Neuroscience, University College London, London, United Kingdom

Submitted 9 August 2006; accepted in final form 23 November 2006

Eye patching has revealed enhanced saccadic latencies or attention effects when orienting toward visual stimuli presented in the temporal versus nasal hemifields of humans. Such behavioral advantages have been tentatively proposed to reflect possible temporal–nasal differences in the retinotectal pathway to the superior colliculus, rather than in the retinogeniculate pathway or visual cortex. However, this has not been directly tested with physiological measures in humans. Here, we examined responses of the human superior colliculus (SC) to contralateral visual field stimulation, using high spatial resolution fMRI, while manipulating which hemifield was stimulated and orthogonally which eye was patched. The SC responded more strongly to visual stimulation when eye-patching made this stimulation temporal rather than nasal. In contrast, the lateral geniculate nucleus (LGN) plus retinotopic cortical areas V1–V3 did not show any temporal–nasal differences and differed from the SC in this respect. These results provide the first direct physiological demonstration in humans that SC shows temporal–nasal differences that LGN and early visual cortex apparently do not. This may represent a temporal hemifield bias in the strength of the retinotectal pathway, leading to a preference for the contralateral hemifield in the contralateral eye.