Biology subjects

Monaco, S.

Publications and source records attributed to Monaco, S..

3 recordsLinked to original sources

bioRxiv2018

Action-specific feature processing in the human visual cortex

Sensorimotor integration involves feedforward and reentrant processing of sensory input. Grasp-related motor activity precedes and is thought to influence visual object processing. Yet, while the importance of reentrant feedback is well established in perception, the top-down modulations for action and the neural circuits involved in this process have received less attention. Do action-specific intentions influence the processing of visual information in the human cortex? Using a cue-separation fMRI paradigm, we found that action-specific instruction (manual alignment vs. grasp) influences the cortical processing of object orientation several seconds after the object had been viewed. This influence occurred as early as in the primary visual cortex and extended to ventral and dorsal visual stream areas. Importantly, this modulation was unrelated to non-specific action planning. Further, the primary visual cortex showed stronger functional connectivity with frontal-parietal areas and the inferior temporal cortex during the delay following orientation processing for align than grasping movements, strengthening the idea of reentrant feedback from dorsal visual stream areas involved in action. To our knowledge, this is the first demonstration that intended manual actions have such an early, pervasive, and differential influence on the cortical processing of vision.

neuroscience↗

bioRxiv2018

Cortical Mechanisms for Reaches Versus Saccades: Progression of Effector-Specificity Through Target Memory to Movement Planning and Execution

Effector-specific cortical mechanisms can be difficult to establish using fMRI, in part because low time resolution might temporally conflate different signals related to target representation, motor planning, and motor execution. Here, we used an event-related fMRI protocol and a cue-separation paradigm to temporally separate these three major sensorimotor stages for saccades vs. reaches. In each trial, subjects (N=12) 1) briefly viewed a target 4-7{degrees} left or right of midline fixation on a touchscreen, followed by an 8 second delay (effector-independent target memory phase), 2) were instructed by an auditory cue to perform a reach or a saccade, followed by a second delay of 8 seconds (effector-specific planning phase), and finally 3) were prompted to move by reaching-to-touch or performing a saccade towards the remembered target (effector-specific execution phase). Our analysis of saccade and reach activation (vs. a non-spatial control task) revealed modest effector-agnostic target memory activity (left AG, bilateral mIPS) followed by independent effector parietofrontal sites and time courses during the motor components of the task, specifically: more medial (pIPS, mIPS, M1, and PMd) activity during both reach planning and execution, and more lateral (mIPS, AG, and FEF) activity only during saccade execution. These motor activations were bilateral, with a left (contralateral) preference for reach. A conjunction analysis revealed that left mIPS and right AG, PCu, SPOC, FEF/PMv and LOTC showed activation for both saccades and reaches. Overall, effector-preference contrasts (reach vs. saccade) revealed significantly more parietofrontal activation for reaches than saccades during both planning and execution, with the exception of FEF. Cross-correlation of reach, saccade, and reach-saccade activation through time revealed correlated activation both within and across effectors in each hemisphere, but with a tendency toward higher correlations in the right hemisphere, especially between the eye and hand. These results demonstrate substantially independent but temporally correlated cortical networks for human eye, hand, and eye-hand control, that follow explicit spatiotemporal rules for effector-specific timing, medial-lateral distribution, and hemispheric lateralization.

neuroscience↗

bioRxiv2018

Transsaccadic feature interactions in multiple reference frames: an fMRIa study

Transsaccadic integration of visual features can operate in various frames of reference, but the corresponding neural mechanisms have not been differentiated. A recent fMRIa (adaptation) study identified two cortical regions in supramarginal gyrus (SMG) and extrastriate cortex that were sensitive to transsaccadic changes in stimulus orientation (Dunkley et al., 2016). Here, we modified this paradigm to identify the neural correlates for transsaccadic comparison of object orientations in: 1) Spatially Congruent (SC), 2) Retinally Congruent (RC) or 3) Spatially Incongruent (SI)) coordinates. Functional data were recorded from 12 human participants while they observed a grating (oriented 45{degrees} or 135{degrees}) before a saccade, and then judged whether a post-saccadic grating (in SC, RC, or SI configuration) had the same or different orientation. Our analysis focused on areas that showed a significant repetition suppression (Different > Same) or repetition enhancement (Same > Different) BOLD responses. Several cortical areas were significantly modulated in all three conditions: premotor/motor cortex (likely related to the manual response), and posterior-middle intraparietal sulcus. In the SC condition, uniquely activated areas included left SMG and left lateral occipitotemporal gyrus (LOtG). In the RC condition, unique areas included inferior frontal gyrus and the left lateral BA 7. In the SI condition, uniquely activated areas included the frontal eye field, medial BA 7, and right LOtG. Overall, the SC results were significantly different from both RC and SI. These data suggest that different cortical networks are used to compare pre- and post-saccadic orientation information, depending on the spatial nature of the task.\n\nSignificance StatementEvery time one makes a saccade, the brain must compare and integrate stored visual information with new information. It has recently been shown that transsaccadic integration of visual object orientation involves specific areas within parietal and occipital cortex (Dunkley et al., 2016). Here, we show that this pattern of cortical activation also depends on the spatial nature of the task: when the visual object is fixed relative to space, the eye, or relative to neither space nor the eye, different frontal, parietal, and occipital regions are engaged. More generally, these findings suggest that different aspects of trans-saccadic integration flexibly employ different cortical networks.

neuroscience↗