Coordinate transformations, sensorimotor integration and the neural basis of saccades to somatosensory targets
Sensory signals of different modalities must be translated into a common coordinate framework in order to produce motor responses involving a common set of muscles. The spatial locations of visual, auditory, and somatosensory stimuli are initially encoded in retinal, head and body coordinates, respectively, and must be translated into a common eye-centered motor frame of reference in order to guide saccadic eye movements to the locations of these stimuli. The superior colliculus is a nucleus in the brain stem which exhibits sensory activity for each of these modalities, as well as motor activity for saccades. Previous work has established that the auditory map in this structure is encoded in an eye centered frame of reference and remains in register with the visual map despite movements of the eyes. In the first chapter, two biologically plausible models employing different algorithms for this coordinate transformation are presented. In chapters 2-4, the behavioral characteristics and neural basis of saccades to somatosensory targets are explored. Monkeys were trained to make saccades to the locations of vibrotactile stimuli delivered to the hands, which were held in fixed positions beneath an opaque barrier. Different saccades were elicited to the same target from different initial eye positions. Somatosensory saccades, like other non-visual saccades, were less accurate, of lower velocity and had longer reaction times than comparable visual saccades (chapter 2). Electrophysiological recordings in the SC showed that somatosensory and visual saccades were represented by a common population of collicular motor cells (chapter 3). Although the discharges of cells for somatosensory and visual saccades were not identical, the differences did not relate in any obvious way to the behavioral differences. Finally, the responses of most collicular somatosensory cells to a somatically identical target depended significantly on eye position (chapter 4). These data suggest that the somatosensory map, like the auditory, visual and motor maps, could be encoded in an eye-centered frame of reference.
Groh, Jennifer Marie, "Coordinate transformations, sensorimotor integration and the neural basis of saccades to somatosensory targets" (1993). Dissertations available from ProQuest. AAI9413840.