Contralateral monocular dominance in anterior visual cortex confirmed by functional magnetic resonance imaging

Although it is known that the damage to anterior striate cortex results in temporal peripheral visual field loss of the contralateral eye in patients with cerebral visual disturbance, the monocularity of anterior striate cortex has not been demonstrated in normal living humans. The aim of this study was to investigate whether this could be shown noninvasively using functional magnetic resonance imaging of the human visual cortex.

Eleven normal volunteers were studied with functional magnetic resonance imaging during alternating monocular visual stimulation using a 1.5 Tesla scanner. The data were motion corrected and spatially normalized to the standard brain. The monocular activation of the visual cortex was compared with the activation by the other eye.

In the individual data analysis, contralateral eye dominance was always observed in the anterior striate cortex. In the group analysis from 11 subjects, the area with contralateral eye dominance was found in the most anterior part of primary visual cortex where the calcarine fissure merged with the parieto-occipital sulcus.

This study shows that the contralateral eye dominance of anterior striate cortex can be detected noninvasively with functional magnetic resonance imaging during monocular visual stimulation. The finding confirms that the anterior striate cortex, where the monocular temporal crescent is represented, is primarily monocular, but the fact that greatest density of retinal ganglion cells and photoreceptors is in the nasal hemiretina must also be taken into account when interpreting these results.