Adaptation to heading direction dissociates the roles of human MST and V6 in the processing of optic flow

Abstract

The extraction of optic flow cues is fundamental for successful locomotion. During forward motion, the focus of expansion (FoE), in conjunction with knowledge of eye position, indicates the direction in which the individual is heading. Therefore, it is expected that cortical brain regions that are involved in the estimation of heading will be sensitive to this feature. To characterize cortical sensitivity to the location of the FoE or, more generally, the center of flow (CoF) during visually simulated self-motion, we carried out a functional MRI (fMRI) adaptation experiment in several human visual cortical areas that are thought to be sensitive to optic flow parameters, namely, V3A, V6, MT/V5, and MST. In each trial, two optic flow patterns were sequentially presented, with the CoF located in either the same or different positions. With an adaptation design, an area sensitive to heading direction should respond more strongly to a pair of stimuli with different CoFs than to stimuli with the same CoF. Our results show such release from adaptation in areas MT/V5 and MST, and to a lesser extent V3A, suggesting the involvement of these areas in the processing of heading direction. The effect could not be explained either by differences in local motion or by attention capture. It was not observed to a significant extent in area V6 or in control area V1. The different patterns of responses observed in MST and V6, areas that are both involved in the processing of egomotion in macaques and humans, suggest distinct roles in the processing of visual cues for self-motion.

Vestibular function in the temporal and parietal cortex: distinct velocity and inertial processing pathways

“…However, using functional MRI, Cardin et al (2012) suggest that only MST is implicated in the extraction of optic flow for computation of heading direction. While MST might provide a representation of heading perception, V6 would rather be concerned with obstacle avoidance during self-motion as inferred by Cardin et al (2012).…”

The functional role of the medial motion area V6

“…Interestingly, despite the V6 preference for self-motion over other types of global motion, a recent study surprisingly suggests that V6 does not encode direction of heading (Cardin et al, 2012). Given that disparity is most informative for nearby objects that generate relatively large retinal disparities, the authors suggested that V6 may be concerned with flow for the purpose of avoiding obstacles during self-motion rather than for providing a representation of heading direction (Cardin et al, 2012).…”

“…Given that disparity is most informative for nearby objects that generate relatively large retinal disparities, the authors suggested that V6 may be concerned with flow for the purpose of avoiding obstacles during self-motion rather than for providing a representation of heading direction (Cardin et al, 2012). The selective preference of V6 for the 3D translational egomotion shown in Sdoia et al (2009) lends support to this view.…”

“…Recent fMRI data suggest that also human V6 contains real-motion cells, since the activity of a medial posterior parietal region that likely includes V6 correlates predominantly with the real motion of objects in the visual field (e.g., Tikhonov et al, 2004; Bartels et al, 2008). Additionally, area V6 has a strong response to translational egomotion (Sdoia et al, 2009) that suggests that this area processes visual egomotion signals to extract information about the relative distance of objects, likely in order to act on them, or to avoid them rather than for providing a representation of heading direction (see also Cardin et al, 2012). The hypothesis that V6 is involved in processing of motion of graspable objects is based also on its tight connectivity with areas involved in grasping (Galletti et al, 2001, 2003), its sensitivity to optic flow patterns combined with disparity cues, most informative for nearby objects (Cardin and Smith, 2011) and its putative preference to near-field stimuli in humans (Quinlan and Culham, 2007).…”

Electrical Stimulation of the Human Homolog of the Medial Superior Temporal Area Induces Visual Motion Blindness

“…Specifically, activations resulting from ipsilateral visual motion stimulation in fMRI experiments have been attributed to hMST assuming that basic neuronal properties would have been preserved across species. Further imaging studies have revealed that hMST indeed resembles its monkey homolog in many important aspects, such as the preference for coherent motion as compared with motion noise (Becker et al, 2008;Fischer et al, 2012;Helfrich et al, 2013) or the selectivity for specific optic flow structures (Wall et al, 2008;Cardin et al, 2012).…”