Activity of Pursuit-Related Neurons in Medial Superior Temporal Area (MST) during Static Roll-Tilt

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Recent studies have shown that rhesus macaques can perceive visual motion-direction in earth-centered coordinates as accurately as humans. We tested whether coordinate frames representing smooth-pursuit and/or visual motion signals in MST are earth-centered to better understand its role in coordinating smooth-pursuit eye movements. In 2 Japanese macaques, we compared preferred directions (re monkeys' head/trunk axis) of pursuit and/or visual motion responses of MSTd neurons while upright and during static whole-body roll-tilt. In the majority (41/51 = 80%) of neurons tested, preferred directions of pursuit and/or visual motion responses were similar while upright and during 40° static roll-tilt. Preferred directions of the remaining 20% of neurons (n = 10) were shifted beyond the range expected from ocular counter-rolling; the maximum shift was 14° and the mean shift was 12°. These shifts, however, were still less than half of the expected shift if MST signals are coded in the earth-centered coordinates. Virtually, all tested neurons (44/46 = 96%) failed to exhibit a significant difference between resting discharge rate while upright and during static roll-tilt while fixating a stationary spot. These results suggest that smooth-pursuit and/or visual motion signals of MST neurons are not coded in the earth-centered coordinates We suggest that these signals are coded in the head-centered coordinate.