Dynamic remapping

The term dynamic remapping has been used in many different ways, but one of the clearest formulations of this concept comes from the mental rotation studies by Georgopoulos et al. (1989; see also REACHING: CODING IN MOTOR CORTEX). In these experiments, monkeys were trained to move a joystick in the direction of a visual stimulus, or 90" counterclockwise from it. The brightness of the stimulus indicated which movement was required on a particular trial: a dim light corresponding to a 90" movement and a bright light to a direct movement. An analysis of reaction time suggested that, by default, the initial motor command always pointed straight at the target and then continuously rotated if the cue indicated a 90" rotation, an interpretation that was subsequently confirmed by single-unit recordings. The term remapping is also commonly used whenever a sensory input in one modality is transformed to the sensory representation in another modality. The best-known example in primates is the remapping of auditory space, which is headcentered in the early stages of auditory processing, into the retinotopic coordinates used in the superior colliculus (Jay and Sparks, 1987; Stein and Meredith, 1993). This type of remapping, equivalent to a change of coordinates, is closely related to sensorimotor transformations. It does not have to be performed over time but could be accomplished by the neuronal circuitry connecting different representations. This review is divided into three parts: In the first part, we briefly describe the types of cortical representations typically encountered in dynamic remapping. We then summarize the results from several physiological studies in which it has been possible to characterize the responses of neurons involved in temporal and spatial remappings. Finally, in the third part, we review modeling efforts to account for these processes.