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Title	Callosal transfer by crossing retinal ganglion cells in human sensory fusion
Abstract Nr.	P101

Purpose	Hemidecussation in the optic chiasm brings the crossed nasal retinal ganglion cells together with the uncrossed temporal retinal ganglion cells, allowing the cortex to analyse the contralateral visual fields. Binocularity is realized by extraction of disparity cues from these signals. Disparity appeared not to be lost after a median split of the optic chiasm in which crossing fibres are transected. It is assumed that by way of callosal tranfer only uncrossed fibres add disparity cues. We separated crossed signals from uncrossed signals to study its contribution to callosal transfer.
Methods	Functional activity in the corpus callosum and visual cortex was assessed using functional magnetic resonance imaging technology while participants with normal binocularity viewed at a central cross on a screen on which stripes with a checkerboard pattern reversal paradigm were projected on the right and the left side, one after the other, of the cross. Functional activity was assessed both during right and left eye occlusion.
Results	Functional activity in the corpus callosum was shown to be higher for the left eye as compared to the right eye, during a visual stimulus on the left side.
Conclusion	We show that callosal activity is significantly higher for crossed ganglion cell signals. In contrast to what is generally assumed, callosal transfer uses crossed retinal input more than uncrossed input.

Authors 1