Dynamic Remapping 3 4
6 The term dynamic remapping has been used in many different 7 ways, but one of the clearest formulations of this concept comes 8 from the mental rotation studies by Georgopoulos et al. (1989) (see 9 also REACHING: CODING IN MOTOR CORTEX). In these experiments 10 monkeys were trained to move a joystick in the direction of a visual 11 stimulus or 90 counterclockwise from it. The brightness of the 12 stimulus indicated which movement was required on a particular 13 trial; a dim light corresponded to a 90 movement and a bright light 14 to a direct movement. An analysis of reaction time suggested that, 15 by default, the initial motor command always pointed straight at 16 the target and then continuously rotated if the cue indicated a 90 17 rotation, an interpretation that was subsequently confirmed by sin18 gle unit recordings. 19 The term remapping is also commonly used whenever a sensory 20 input in one modality is transformed to a sensory representation in 21 another modality. The best-known example in primates is the re22 mapping of auditory space, from head-centered in the early stages 23 of auditory processing to the retinotopic coordinates used in the 24 superior colliculus (Jay and Sparks, 1987). This type of remapping, 25 equivalent to a change of coordinates, is closely related to senso26 rimotor transformations. It does not have to be performed over time 27 but could be accomplished by the neuronal circuitry connecting 28 different representations. 29 This review is divided into three parts. In the first part, we briefly 30 describe the types of cortical representations typically encountered 31 in dynamic remapping. We then summarize the results from several 32 physiological studies where it has been possible to characterize the 33 responses of neurons involved in temporal and spatial remappings. 34 Finally, in the third part, we review modeling efforts to account for 35 these processes.