The cerebral cortex must have access to an eye position signal, as humans can report passive changes in eye position in total darkness, and visual responses in many cortical areas are modulated by eye position. The source of this signal is unknown. Here we demonstrate a representation of eye position in monkey primary somatosensory cortex, in the representation of the trigeminal nerve, near cells with a tactile representation of the contralateral brow. The neurons have eye position signals that increase monotonically with increasing orbital eccentricity from near the center of gaze, with directionally selectivity tuned in a Gaussian manner. All directions of eye position are represented in a single hemisphere. The signal is proprioceptive, because it can be obliterated by anesthetizing the contralateral orbit. It is not related to foveal or peripheral visual stimulation, and it represents the position of the eye in the head and not the angle of gaze in space.

Structural asymmetries in the supratemporal plane of the human brain are often cited as the anatomical basis for the lateralization of language predominantly to the left hemisphere. However, similar asymmetries are found for structures mediating earlier events in the auditory processing stream, suggesting that functional lateralization may occur even at the level of primary auditory cortex. We tested this hypothesis using functional magnetic resonance imaging to evaluate human auditory cortex responses to monaurally presented tones. Relative to silence, tones presented separately to either ear produced greater activation in left than right Heschl's gyrus, the location of primary auditory cortex. This functional lateralization for primary auditory cortex is distinct from the contralateral dominance reported for other mammals, including nonhuman primates, and may have contributed to the evolution of a unique role for the left hemisphere in language processing.

Humans and monkeys mislocalize targets flashed around the time of a saccade. Here, we present data from three monkeys on a double-step task with a 100ms target duration. All three subjects mislocalized targets that were flashed around the time of the first saccade, in spite of long intersaccadic intervals. The error was consistently in the direction opposite that of the saccade, and occurred in some cases when the target presentation was entirely presaccadic. This is inconsistent with a theory invoking a damped representation of eye position, but it is consistent with the hypothesis that it is due to an error in peri-saccadic remapping.

The lateral intraparietal area (area LIP) contains a multimodal representation of extra-personal space. To further examine this representation, we trained rhesus monkeys on the predictive-cueing task. During this task, monkeys shifted their gaze to a visual target whose location was predicted by the location of an auditory or visual cue. We found that, when the sensory cue was at the same location as the visual target, the monkeys' mean saccadic latency was faster than when the sensory cue and the visual target were at different locations. This difference in mean saccadic latency was the same for both auditory cues and visual cues. Despite the fact that the monkeys used auditory and visual cues in a similar fashion, LIP neurons responded more to visual cues than to auditory cues. This modality-dependent activity was also seen during auditory and visual memory-guided saccades but to a significantly greater extent than during the predictive-cueing task. Additionally, we found that the firing rate of LIP neurons was inversely correlated with saccadic latency. This study indicates further that modality-dependent differences in LIP activity do not simply reflect differences in sensory processing but also reflect the cognitive and behavioral requirements of a task.

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