Eye-centered, head-centered, and intermediate coding of remembered sound locations in area LIP

Abstract

1. The lateral intraparietal area (LIP) of the posterior parietal cortex lies within the dorsal cortical stream for spatial vision and processes visual information to plan saccadic eye movements. We investigated how LIP neurons respond when a monkey makes saccades to the remembered location of sound sources in the absence of visual stimulation. 2. Forty-three (36%) of the 118 neurons sampled showed significant auditory triggered activity during the memory period. This figure is similar to the proportion of cells showing visually triggered memory activity. 3. Of the cells showing auditory memory activity, 44% discharged in an eye-centered manner, similar to the way in which LIP cells discharge for visually initiated saccades. Another 33% responded in head-centered coordinates, and the remaining 23% had responses intermediate between the two reference frames. 4. For a substantial number of cells in all three categories, the magnitude of the response was modulated by eye position. Similar orbital "gain fields" had been shown previously for visual saccades. 5. We propose that area LIP is either at the origin of, or participates in, the transformation of auditory signals for oculomotor purposes, and that orbital gains on the discharge are part of this process. 6. Finally, we suggest that, by the level of area LIP, cells are concerned with the abstract quality of where a stimulus is in space, independent of the exact nature of the stimulus.