Gaze effects in the cerebral cortex: reference frames for space coding and action.

Visual information is mapped with respect to the retina within the early stages of the visual cortex. On the other hand, the brain has to achieve a representation of object location in a coordinate system that matches the reference frame used by the motor cortex to code reaching movement in space. The mechanism of the necessary coordinate transformation between the different frames of reference from the visual to the motor system as well as its localization within the cerebral cortex is still unclear. Coordinate transformation is traditionally described as a series of elementary computations along the visuomotor cortical pathways, and the motor system is thought to receive target information in a body-centered reference frame. However, neurons along these pathways have a number of similar properties and receive common input signals, suggesting that a non-retinocentric representation of object location in space might be available for sensory and motor purposes throughout the visuomotor pathway. This paper reviews recent findings showing that elementary input signals, such as retinal and eye position signals, reach the dorsal premotor cortex. We will also compare eye position effects in the premotor cortex with those described in the posterior parietal cortex. Our main thesis is that appropriate sensory input signals are distributed across the visuomotor continuum, and could potentially allow, in parallel, the emergence of multiple and task-dependent reference frames.