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 (i.e. objective) motion are the product of integration between motion signals on the retina and efference copies of eye movements. Human areas V3A and V6 have previously been shown to have strong objective (‘real’) motion responses. Here we used high-resolution laminar fMRI at ultra-high magnetic field (9.4T) in human subjects to examine motion integration across cortical depths in these areas. We found an increased preference for objective motion in areas V3A and V6+ i.e. V6 and possibly V6A towards the upper layers. When laminar responses were detrended to remove the upper-layer bias present in all responses, we found a unique, condition-specific laminar profile in V6+, showing reduced mid-layer responses for retinal motion only. The results provide evidence for differential, motion-type dependent laminar processing in area V6+. Mechanistically, the mid-layer dip suggests a special contribution of retinal motion to integration, either in the form of a subtractive (inhibitory) mid-layer input, or in the form of feedback into extragranular or infragranular layers. The results show that differential laminar signals can be measured in high-level motion areas in the human occipitoparietal cortex, opening the prospect of new mechanistic insights using non-invasive brain imaging.
Significance Statement Visual stability and our ability to differentiate between self-induced and real motion are central to our visual sense. Both require the integration of two signals – retinal motion and copies of muscle commands used for eye movements (efference copies). A reasonable assumption is that either the efference copy or the result of integration will be conveyed to high-level visual regions along with visual retinal input, possibly differentially across cortical depth as the input sources differ. Our ultra-high field recordings present the first laminar evidence of differential signal processing of retinal and objective motion signals in area V6+, and present a first window into a mechanistic understanding of visual high-level motion processing.
Competing Interest Statement
The authors have declared no competing interest.
