Flexible egocentric and allocentric representations of heading signals in parietal cortex.

By systematically manipulating head position relative to the body and eye position relative to the head, previous studies have shown that vestibular tuning curves of neurons in the ventral intraparietal (VIP) area remain invariant when expressed in body-/world-centered coordinates. However, body orientation relative to the world was not manipulated; thus, an egocentric, body-centered representation could not be distinguished from an allocentric, world-centered reference frame. We manipulated the orientation of the body relative to the world such that we could distinguish whether vestibular heading signals in VIP are organized in body- or world-centered reference frames. We found a hybrid representation, depending on gaze direction. When gaze remained fixed relative to the body, the vestibular heading tuning of VIP neurons shifted systematically with body orientation, indicating an egocentric, body-centered reference frame. In contrast, when gaze remained fixed relative to the world, this representation changed to be intermediate between body- and world-centered. We conclude that the neural representation of heading in posterior parietal cortex is flexible, depending on gaze and possibly attentional demands.