Coordinate transformation from retinotopic coordinates to craniotopic coordinates

The neural mechanism for coordinate transformation is an important issue for understanding how the brain constructs body-centered motor programs from retinotopically-organized visual inputs. Although visual properties examined in many areas outside the striate cortex have been shown to be arranged retinotopically, some parietal neurons and ventral premotor neurons encode locations of visual stimuli craniotopically. These indicate that retinotopically-organized visual information is transformed craniotopically within the brain. The response magnitude of posterior parietal neurons to visual stimuli presented at identical retinal positions was affected by the monkey's angle of gaze. A computer simulation revealed that the angle-of- gaze effect reflects a neural mechanism related to transformation from retinotopically-coded visual information to head-centered spatial information. This result suggests that the transformation from retinotopic coordinate to head-centered coordinate is achieved in the posterior parietal cortex. However, the angle-of-gaze effect has been observed not only in the parietal cortex but also in the V3A and frontal cortex, suggesting that coordinate transformation could be performed in parallel in different cortical areas.