Velji-Ibrahim, J. | bioRxiv Science

bioRxiv2019

Parietal Cortex Integrates Visual and Oculomotor Signals to Update Grasp Plans

Coordinated reach-to-grasp movements are often accompanied by rapid eye movements (saccades) that displace the desired object image relative to the retina. Parietal cortex compensates for this by updating reach goals relative to current gaze direction, but its role in the integration of oculomotor and visual orientation signals for updating grasp plans is unknown. Based on a recent perceptual experiment, we hypothesized that inferior parietal cortex (specifically supramarginal gyrus; SMG) integrates saccade and visual signals to update grasp plans in more superior parietal areas. To test this hypothesis, we employed a functional magnetic resonance adaptation paradigm, where saccades sometimes interrupted grasp preparation toward a briefly presented object that later reappeared (with the same/different orientation) just before movement. Right SMG and several parietal grasp areas, namely left anterior intraparietal sulcus (aIPS) and bilateral superior parietal lobe (SPL), met our criteria for transsaccadic orientation integration: during movement preparation, they showed task-dependent saccade modulations and, during grasp execution, they were specifically sensitive to changes in object orientation that followed saccades. Finally, SMG showed enhanced functional connectivity with both prefrontal saccade areas (consistent with oculomotor input) and aIPS / SPL (consistent with sensorimotor output). These results support the general role of parietal cortex for the integration of visuospatial perturbations, and provide specific cortical modules for the integration of oculomotor and visual signals for grasp updating. Significance StatementThe cortical mechanisms that update reach goals during eye movements are well documented, but it is not known how object features are linked to oculomotor signals when updating grasp plans. Here, we employed functional magnetic resonance imaging adaptation (fMRIa) and functional connectivity analysis to identify a cluster of inferior parietal (supramarginal gyrus) and superior parietal (intraparietal and superior parietal) regions that show functional connectivity with frontal cortex saccade centers, and also show saccade-specific modulations during unexpected changes in object / grasp orientation. This provides a network - complementary to the goal updater network - that integrates visuospatial updating into grasp plans, and may help explain some of the more complex symptoms associated with parietal damage such as constructional ataxia.

neuroscience↗

bioRxiv2018

Action intention modulates the representation of object features in early visual cortex

The role of the visual cortex has been extensively studied to determine its role in object recognition but to a lesser degree to determine how action planning influences the representation of objects features. We used functional MRI and pattern classification methods to determine if during action planning, object features (orientation and location) could be decoded in an action-dependent way. Sixteen human participants used their right dominant hand to perform movements (Align or Open reach) towards one of two 3D-real oriented objects that were simultaneously presented and placed on either side of a fixation cross. While both movements required aiming toward target location, Align but not Open reach movements required participants to precisely adjust hand orientation. Therefore, we hypothesized that if the representation of object features is modulated by the upcoming action, pre-movement activity pattern would allow more accurate dissociation between object features in Align than Open reach tasks. We found such dissociation in the anterior and posterior parietal cortex, as well as in the dorsal premotor cortex, suggesting that visuomotor processing is modulated by the upcoming task. The early visual cortex showed significant decoding accuracy for the dissociation between object features in the Align but not Open reach task. However, there was no significant difference between the decoding accuracy in the two tasks. These results demonstrate that movement-specific preparatory signals modulate object representation in the frontal and parietal cortex, and to a lesser extent in the early visual cortex, likely through feedback functional connections.

neuroscience↗