Differential Responses to a Visual Self-Motion Signal in Human Medial Cortical Regions Revealed by Wide-View Stimulation.
ABSTRACT: Vision is important for estimating self-motion, which is thought to involve optic-flow processing. Here, we investigated the fMRI response profiles in visual area V6, the precuneus motion area (PcM), and the cingulate sulcus visual area (CSv)-three medial brain regions recently shown to be sensitive to optic-flow. We used wide-view stereoscopic stimulation to induce robust self-motion processing. Stimuli included static, randomly moving, and coherently moving dots (simulating forward self-motion). We varied the stimulus size and the presence of stereoscopic information. A combination of univariate and multi-voxel pattern analyses (MVPA) revealed that fMRI responses in the three regions differed from each other. The univariate analysis identified optic-flow selectivity and an effect of stimulus size in V6, PcM, and CSv, among which only CSv showed a significantly lower response to random motion stimuli compared with static conditions. Furthermore, MVPA revealed an optic-flow specific multi-voxel pattern in the PcM and CSv, where the discrimination of coherent motion from both random motion and static conditions showed above-chance prediction accuracy, but that of random motion from static conditions did not. Additionally, while area V6 successfully classified different stimulus sizes regardless of motion pattern, this classification was only partial in PcM and was absent in CSv. This may reflect the known retinotopic representation in V6 and the absence of such clear visuospatial representation in CSv. We also found significant correlations between the strength of subjective self-motion and univariate activation in all examined regions except for primary visual cortex (V1). This neuro-perceptual correlation was significantly higher for V6, PcM, and CSv when compared with V1, and higher for CSv when compared with the visual motion area hMT+. Our convergent results suggest the significant involvement of CSv in self-motion processing, which may give rise to its percept.
Project description:We investigated how interactions between monocular motion parallax and binocular cues to depth vary in human motion areas for wide-field visual motion stimuli (110 × 100°). We used fMRI with an extensive 2 × 3 × 2 factorial blocked design in which we combined two types of self-motion (translational motion and translational + rotational motion), with three categories of motion inflicted by the degree of noise (self-motion, distorted self-motion, and multiple object-motion), and two different view modes of the flow patterns (stereo and synoptic viewing). Interactions between disparity and motion category revealed distinct contributions to self- and object-motion processing in 3D. For cortical areas V6 and CSv, but not the anterior part of MT(+) with bilateral visual responsiveness (MT(+)/b), we found a disparity-dependent effect of rotational flow and noise: When self-motion perception was degraded by adding rotational flow and moderate levels of noise, the BOLD responses were reduced compared with translational self-motion alone, but this reduction was cancelled by adding stereo information which also rescued the subject's self-motion percept. At high noise levels, when the self-motion percept gave way to a swarm of moving objects, the BOLD signal strongly increased compared to self-motion in areas MT(+)/b and V6, but only for stereo in the latter. BOLD response did not increase for either view mode in CSv. These different response patterns indicate different contributions of areas V6, MT(+)/b, and CSv to the processing of self-motion perception and the processing of multiple independent motions.
Project description:To plan movements toward objects our brain must recognize whether retinal displacement is due to self-motion and/or to object-motion. Here, we aimed to test whether motion areas are able to segregate these types of motion. We combined an event-related functional magnetic resonance imaging experiment, brain mapping techniques, and wide-field stimulation to study the responsivity of motion-sensitive areas to pure and combined self- and object-motion conditions during virtual movies of a train running within a realistic landscape. We observed a selective response in MT to the pure object-motion condition, and in medial (PEc, pCi, CSv, and CMA) and lateral (PIC and LOR) areas to the pure self-motion condition. Some other regions (like V6) responded more to complex visual stimulation where both object- and self-motion were present. Among all, we found that some motion regions (V3A, LOR, MT, V6, and IPSmot) could extract object-motion information from the overall motion, recognizing the real movement of the train even when the images remain still (on the screen), or moved, because of self-movements. We propose that these motion areas might be good candidates for the "flow parsing mechanism," that is the capability to extract object-motion information from retinal motion signals by subtracting out the optic flow components.
Project description:The principal visual cue to self-motion (egomotion) is optic flow, which is specified in terms of local 2D velocities in the retinal image without reference to depth cues. However, in general, points near the center of expansion of natural flow fields are distant, whereas those in the periphery are closer, creating gradients of horizontal binocular disparity. To assess whether the brain combines disparity gradients with optic flow when encoding egomotion, stereoscopic gradients were applied to expanding dot patterns presented to observers during functional MRI scanning. The gradients were radially symmetrical, disparity changing as a function of eccentricity. The depth cues were either consistent with egomotion (peripheral dots perceived as near and central dots perceived as far) or inconsistent (the reverse gradient, central dots near, peripheral dots far). The BOLD activity generated by these stimuli was compared in a range of predefined visual regions in 13 participants with good stereoacuity. Visual area V6, in the parieto-occipital sulcus, showed a unique pattern of results, responding well to all optic flow patterns but much more strongly when they were paired with consistent rather than inconsistent or zero-disparity gradients. Of the other areas examined, a region of the precuneus and parietoinsular vestibular cortex also differentiate between consistent and inconsistent gradients, but with weak or suppressive responses. V3A, V7, MT, and ventral intraparietal area responded more strongly in the presence of a depth gradient but were indifferent to its depth-flow congruence. The results suggest that depth and flow cues are integrated in V6 to improve estimation of egomotion.
Project description:The analysis and representation of visual cues to self-motion (egomotion) is primarily associated with cortical areas MST, VIP, and (recently) cingulate sulcus visual area (CSv). Various other areas, including visual areas V6 and V6A, and vestibular areas parietoinsular vestibular cortex (PIVC), putative area 2v (p2v), and 3aNv, are also potentially suited to processing egomotion (in some cases based on multisensory cues), but it is not known whether they are in fact involved in this process. In a functional magnetic resonance imaging (fMRI) experiment, we presented human participants with 2 types of random dot kinematograms. Both contained coherent motion but one simulated egomotion while the other did not. An area in the parieto-occipital sulcus that may correspond to V6, PIVC, and p2v were all differentially responsive to egomotion-compatible visual stimuli, suggesting that they may be involved in encoding egomotion. More generally, we show that the use of such stimuli provides a simple and reliable fMRI localizer for human PIVC and p2v, which hitherto required galvanic or caloric stimulation to be identified.
Project description:Visuo-vestibular integration is crucial for locomotion, yet the cortical mechanisms involved remain poorly understood. We combined binaural monopolar galvanic vestibular stimulation (GVS) and functional magnetic resonance imaging (fMRI) to characterize the cortical networks activated during antero-posterior and lateral stimulations in humans. We focused on functional areas that selectively respond to egomotion-consistent optic flow patterns: the human middle temporal complex (hMT+), V6, the ventral intraparietal (VIP) area, the cingulate sulcus visual (CSv) area and the posterior insular cortex (PIC). Areas hMT+, CSv, and PIC were equivalently responsive during lateral and antero-posterior GVS while areas VIP and V6 were highly activated during antero-posterior GVS, but remained silent during lateral GVS. Using psychophysiological interaction (PPI) analyses, we confirmed that a cortical network including areas V6 and VIP is engaged during antero-posterior GVS. Our results suggest that V6 and VIP play a specific role in processing multisensory signals specific to locomotion during navigation.
Project description:The cortical network that processes visual cues to self-motion was characterized with functional magnetic resonance imaging in 3 awake behaving macaques. The experimental protocol was similar to previous human studies in which the responses to a single large optic flow patch were contrasted with responses to an array of 9 similar flow patches. This distinguishes cortical regions where neurons respond to flow in their receptive fields regardless of surrounding motion from those that are sensitive to whether the overall image arises from self-motion. In all 3 animals, significant selectivity for egomotion-consistent flow was found in several areas previously associated with optic flow processing, and notably dorsal middle superior temporal area, ventral intra-parietal area, and VPS. It was also seen in areas 7a (Opt), STPm, FEFsem, FEFsac and in a region of the cingulate sulcus that may be homologous with human area CSv. Selectivity for egomotion-compatible flow was never total but was particularly strong in VPS and putative macaque CSv. Direct comparison of results with the equivalent human studies reveals several commonalities but also some differences.
Project description:<h4>Introduction</h4>Spatial navigation is a complex cognitive skill that varies between individuals, and the mechanisms underlying this variability are not clear. Studying simpler components of spatial navigation may help illuminate factors that contribute to variation in this complex skill; path integration is one such component. Optic flow provides self-motion information while moving through an environment and is sufficient for path integration. This study aims to investigate whether self-reported navigation ability is related to information transfer between optic flow-sensitive (OF-sensitive) cortical regions and regions important to navigation during environmental spatial tasks.<h4>Methods</h4>Functional magnetic resonance imaging was used to define OF-sensitive regions and map their functional connectivity (FC) with the retrosplenial cortex and hippocampus during visual path integration (VPI) and turn counting (TC) tasks. Both tasks presented visual self-motion through a real-world environment. Correlations predicting a positive association between self-reported navigation ability (measured with the Santa Barbara Sense of Direction scale) and FC strength between OF-sensitive regions and retrosplenial cortex and OF-sensitive regions and the hippocampus were performed.<h4>Results</h4>During VPI, FC strength between left cingulate sulcus visual area (L CSv) and right retrosplenial cortex and L CSv and right hippocampus was positively associated with self-reported navigation ability. FC strength between right cingulate sulcus visual area (R CSv) and right retrosplenial cortex during VPI was also positively associated with self-reported navigation ability. These relationships were specific to VPI, and whole-brain exploratory analyses corroborated these results.<h4>Conclusions</h4>These findings support the hypothesis that perceived spatial navigation ability is associated with communication strength between OF-sensitive and navigationally relevant regions during visual path integration, which may represent the transformation accuracy of visual motion information into internal spatial representations. More broadly, these results illuminate underlying mechanisms that may explain some variability in spatial navigation ability.
Project description:Human visual area V6, in the parieto-occipital sulcus, is thought to have an important role in the extraction of optic flow for the monitoring and guidance of self-motion (egomotion) because it responds differentially to egomotion-compatible optic flow when compared to: (a) coherent but egomotion-incompatible flow (Cardin & Smith, 2010), and (b) incoherent motion (Pitzalis et al., 2010). It is not clear, however, whether V6 responds more strongly to egomotion-incompatible global motion than to incoherent motion. This is relevant not only for determining the functional properties of V6, but also in order to choose optimal stimuli for localising V6 accurately with fMRI. Localisation with retinotopic mapping is difficult and there is a need for a simple, reliable method. We conducted an event-related 3T fMRI experiment in which participants viewed a display of dots which either: a) followed a time-varying optic flow trajectory in a single, egomotion-compatible (EC) display; b) formed an egomotion-incompatible (EI) 3 × 3 array of optic flow patches; or c) moved randomly (RM). Results from V6 show an ordering of response magnitudes: EC > EI > RM. Neighbouring areas V3A and V7 responded more strongly to EC than to RM, but about equally to EC and EI. Our results suggest that although V6 may have a general role in the extraction of global motion, in clear contrast to neighbouring motion areas it is especially concerned with encoding EC stimuli. They suggest two strategies for localising V6: (1) contrasting EC and EI; or (2) contrasting EC and RM, which is more sensitive but carries a risk of including voxels from neighbouring regions that also show a EC > RM preference.
Project description:Motion processing regions apart from V5+/MT+ are still relatively poorly understood. Here, we used functional magnetic resonance imaging to perform a detailed functional analysis of the recently described cingulate sulcus visual area (CSv) in the dorsal posterior cingulate cortex. We used distinct types of visual motion stimuli to compare CSv with V5/MT and MST, including a visual pursuit paradigm. Both V5/MT and MST preferred 3D flow over 2D planar motion, responded less yet substantially to random motion, had a strong preference for contralateral versus ipsilateral stimulation, and responded nearly equally to contralateral and to full-field stimuli. In contrast, CSv had a pronounced preference to 2D planar motion over 3D flow, did not respond to random motion, had a weak and nonsignificant lateralization that was significantly smaller than that of MST, and strongly preferred full-field over contralateral stimuli. In addition, CSv had a better capability to integrate eye movements with retinal motion compared with V5/MT and MST. CSv thus differs from V5+/MT+ by its unique preference to full-field, coherent, and planar motion cues. These results place CSv in a good position to process visual cues related to self-induced motion, in particular those associated to eye or lateral head movements.
Project description:In humans, the posterior cingulate cortex contains an area sensitive to visual cues to self-motion. This cingulate sulcus visual area (CSv) is structurally and functionally connected with several (multi)sensory and (pre)motor areas recruited during locomotion. In nonhuman primates, electrophysiology has shown that the cingulate cortex is also related to spatial navigation. Recently, functional MRI in macaque monkeys identified a cingulate area with similar visual properties to human CSv. In order to bridge the gap between human and nonhuman primate research, we examined the structural and functional connectivity of putative CSv in three macaque monkeys adopting the same approach as in humans based on diffusion MRI and resting-state functional MRI. The results showed that putative monkey CSv connects with several visuo-vestibular areas (e.g., VIP/FEFsem/VPS/MSTd) as well as somatosensory cortex (e.g., dorsal aspects of areas 3/1/2), all known to process sensory signals that can be triggered by self-motion. Additionally, strong connections are observed with (pre)motor areas located in the dorsal prefrontal cortex (e.g., F3/F2/F1) and within the anterior cingulate cortex (e.g., area 24). This connectivity pattern is strikingly reminiscent of that described for human CSv, suggesting that the sensorimotor control of locomotion relies on similar organizational principles in human and nonhuman primates.