Grant: Operating Grant

Whether running to catch a ball or turning to reach for a coffee cup, our ability to interact behaviorally with the environment depends critically on knowing our motion and orientation in space. As we move, the brain integrates multiple sensory signals to compute estimates of our self-motion. However, this poses a challenge because the way that sensory signals must be combined and interpreted depends on the conditions (context) in which they are sensed. One important contextual influence is gravity. Gravity provides a world-fixed reference (i.e., which way is up/down) for interpreting our motion. To navigate during locomotion or maintain upright posture we rely on information about our motion with respect to this fixed spatial reference. However, because each of our sensors is attached to different body parts, no one sensor provides this information. For example, our vestibular sensors (semicircular canals and otoliths) signal head movement along axes fixed in the head. Thus, when running to catch a ball, the same movement in space (e.g., forward motion) is sensed by one combination of sensors when the head is upright and a different set when the head is tilted backward to look up at the ball. To maintain balance as we run, we must also know our tilt relative to gravity. This too requires combining sensory signals in a head-orientation-dependent way. Gravity thus serves as a fundamental contextual cue for interpreting the motion our sensors encode. The goal of this work is to investigate the contextual role of gravity on the integration of multisensory (vestibular, visual) signals in the brainstem and cerebellum. By better understanding how the brain computes spatial motion estimates that are essential for tasks such as navigation and postural control, it is hoped that this research will lead to improved rehabilitative strategies to counteract spatial disorientation, balance and dizziness disorders, debilitating problems that are particularly common in the elderly.