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Abstract:
Neural mechanisms underlying a stable perception of the world during pursuit eye movements are not fully understood. Both, perceptual stability as well as perception of real-world motion are the product of multi-modal integration between retinal motion (visual motion signals) and efference copies of eye movements (non-visual motion signals). The comparison between these two signals allows differentiating between self-induced motion and external, real-world motion. Recently, pursuit-paradigms revealed that human area V3A responds to motion predominantly in a world-centered rather than in a retina-centered reference frame (Fischer et al., 2012). This indicates that V3A integrates retinal motion with non-retinal eye-movement signals. In this study we combined ultra-high-field (9.4T) human fMRI, state of the art pulse sequences, and laminar analysis to find out if there is a differential involvement of cortical layers in the processing of real world motion compared to retinal motion in area V3A. We used a 2D GE EPI sequence with 0.8 mm isotropic resolution to measure BOLD signal at different cortical depths while subjects performed a visual pursuit task. The paradigm involved a 2x2 design containing real motion and visual pursuit, which allowed separating responses to retinal and real motion while fully controlling for pursuit-related effects. A laminar surface-based analysis method was used to study the relationship between spatial localization and activation strength as a function of cortical depth by sampling the BOLD signal from the superficial, middle, or deep cortical lamina in area V3A.
The results show that signals related to retinal motion were evenly spread across layers with a bias towards deep layers of V3A while real-motion responses had a gradient with a peak in superficial layers. The differential laminar response profile is compatible with differential local processing for the two motion types. The stronger involvement of superficial layers during real motion processing may be indicative of feedback related processing, possibly through mediation of efference-copy related signals from higher-level regions such as parietal cortex or smooth pursuit fields of the frontal eye fields with which V3A has direct connections. Future studies are needed to clarify the reasons for differential laminar responses and to identify communication pathways leading to V3A.
