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Brian Lee, Bijan Pesaran, Richard A. Andersen; Self-motion is represented in an eye-centered coordinate frame in SMTd. Journal of Vision 2006;6(6):111. doi: https://doi.org/10.1167/6.6.111.
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© ARVO (1962-2015); The Authors (2016-present)
MSTd neurons are tuned to the focus of expansion of the visual image, but it is not known in which coordinate frame the tuning curves are represented. Since visual signals generated by self-motion are used to guide movement of the subject through the environment, they likely become represented in body or world coordinate frames at later stations in the visual-motor pathway. We performed experiments to determine whether focus tuning curves in MSTd are represented in eye, head, body, or world coordinates. Since MSTd neurons adjust their focus tuning curves during pursuit eye movements to compensate for changes in pursuit and translation speed that distort the visual image, the coordinate frame was determined for three separate conditions: fixed gaze, real pursuit, and simulated pursuit. It is possible that different coordinate frames are used to compensate for tuning curve shifts due to retinal and extraretinal signals. Focus tuning was determined at five eye positions, six degrees apart, along the preferred direction of pursuit. We recorded extracellular responses from 80 MSTd neurons in two rhesus monkeys (Macaca mulatta). We found that the expansion focus tuning curves were aligned in an eye-centered coordinate frame as opposed to head, body, or world-centered coordinate frames for almost all cells (fixed gaze: 77/80; real pursuit: 77/80; simulated pursuit 74/80; t-test, p<0.05). These results indicate that MSTd neurons represent heading in an eye-centered coordinate frame in an early part of the visual-motor pathway that integrates retinal and extraretinal signals.
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