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Abstract:
Melanopsin is expressed in a subset of retinal ganglion cells and mediates non-image-forming responses to light. It is unknown whether melanopsin contributes to conscious vision. We obtained fMRI data from four subjects who viewed spectral pulses that selectively targeted either melanopsin or the cones (3 sec, cosine windowed, 5 contrasts between 25% to 400%; separate backgrounds used for melanopsin and cone-directed stimuli to maximize available contrast; melanopsin background: 110 cd/m2, 3.39 log10 scotopic Trolands). The melanopsin and cone-directed stimuli evoke distinct pupil light responses. Melanopsin-directed stimulation produces fMRI responses in the visual cortex larger than can be easily explained by imperfections in cone silencing. Both melanopsin and cone-directed stimuli produce monotonic contrast-response functions. We find evidence that melanopsin-directed stimulation produces a more temporally extended fMRI response, consistent with known properties of the melanopsin-containing RGCs.
