A Brief Exposure to Leftward Prismatic Adaptation Enhances the Representation of the Ipsilateral, Right Visual Field in the Right Inferior Parietal Lobule

Abstract

A brief exposure to rightward prismatic adaptation (PA) was shown to shift visual field representation within the inferior parietal lobule from the right to the left hemisphere. This change in hemispheric dominance could be interpreted as i) a general effect of discrepancy in visuo-motor alignment caused by PA or ii) a direction-specific effect of rightward PA. To test these hypotheses, we compared the effects of rightward and leftward PA on visual representation in normal human subjects. Three groups of normal subjects underwent an fMRI evaluation using a simple visual detection task before and after brief PA exposure using leftward- or rightward-deviating prisms or no prisms (L-PA, R-PA, Neutral groups). A two-way ANOVA Group x Session revealed a significant interaction suggesting that PA-induced modulation is direction-specific. Post hoc analysis showed that L-PA enhanced the representation of the right visual field within the right inferior parietal lobule. Thus, a brief exposure to L-PA enhanced right hemispheric dominance within the ventral attentional system, which is the opposite effect of the previously described shift in hemispheric dominance following R-PA. The direction-specific effects suggest that the underlying neural mechanisms involve the fine-tuning of specific visuo-motor networks. The enhancement of right hemispheric dominance following L-PA offers a parsimonious explanation for neglect-like symptoms described previously in normal subjects.

Significance Statement L-PA increased the representation of the right visual field within the right IPL. This enhancement of the right hemispheric dominance within the ventral attentional system contradicts the dominance shift, from right to left hemisphere, which is induced by R-PA. Thus, the PA-induced modulation of hemispheric dominance within the ventral attentional system is sensitive to the direction of prismatic deviation and is likely to depend on fine-tuning of specific visuo-motor networks. The overemphasis of right visual field representation within the (right) ventral attentional system offers a parsimonious explanation for neglect-like effects following L-PA.