Head position modulates activity in the human parietal eye fields.

For us to interact with our environment we need to know where objects are around us, relative to our body. In monkeys, a body-centered map of visual space is known to exist within the parietal eye fields. This map is formed by the modulation of retinal responses by gain fields to gaze position. In humans, no map of body-centered space has yet been discovered but clinical data suggest that the right parietal lobe is predominantly responsible for visuospatial function. Using functional MRI, we have been able to demonstrate that an area in the intraparietal sulcus of humans has properties very similar to the parietal eye fields of monkeys. This area demonstrates BOLD signal changes related to the visual, saccadic, and memory components of saccade tasks that are analogous to the visual, saccadic, and memory responses of neurons within the parietal eye fields of monkeys. More importantly, the amount of signal change seen in this region is modulated by head position relative to the body, suggesting that a gain field dependent body-centered representation of space exists bilaterally within the parietal lobes in humans.