The cortical topography of self-motion perception.

When performing motor actions such as picking up a cup from a table we need to have reliable information about the location and size of the object. However, most actions are performed while we are in motion, meaning that the change in our position relative to our surroundings needs to be incorporated also. Optic flow, the change of the optic array when we move, provides important information about our self-motion and about the depth of objects in our surrounding. In a series of psychophysical and neuroimaging studies, we examined the cortical organization underlying visual flow processing. Using a custom-built MRI visual presentation set-up, we were able to measure cortical activity in healthy subjects exposed to wide field presented optic flow patterns. First, we examined processing of visual signals of self-rotation of the eye and head. We found that several areas within the human motion network contain adjacent visual representations of self-motion, each most sensitive to rotation in a different reference frame (i.e., that of the eye or head). A subsequent experiment revealed that medial motion areas but not lateral motion areas are also sensitive to translation of the head in space, as signalled by monocular and binocular depth cues. A representation of head motion might facilitate the integration between self-motion information from visual and vestibular origin. Yet, an examination of the cortical organization and sensitivity to visually defined head rotation did not reveal a strong interaction with vestibular head rotation signals, as has been found in the cerebellum of other mammals. Rather, visual representations of motion of the head in space likely facilitate visually guided actions. It allows the visual system to be fast, flexible, and adaptable during all kinds of motor actions that require different motion reference frames. For example, taking a sip from a cup requires knowledge about the motion of the cup relative to your head, whereas putting in contact lenses requires knowledge of the lens’ motion towards your eye