Sensorimotor transformation in the macaque parietal reach region.

摘要

This dissertation explores the sensorimotor transformation in the parietal reach region (PRR). First, we investigated whether PRR neurons are limb-specific. During the time of reach planning, some PRR neurons selectively represented target location for the contralateral limb but not the ipsilateral limb, whereas others represented target location for either limb. The activity predicted the reach reaction times of the contralateral limb only. These findings suggest that, even though PRR is at an early stage of the sensorimotor transformation, it is limb-specific.;Next, we examined the use of eye and arm position gain fields in PRR. Strikingly, at the individual cell level, eye and arm position gain fields are negatively coupled to one another. At the population level, the two gain fields are configured to be similar in magnitude but opposite in sign. As a result, neuronal firing is modulated in proportion to the distance between the eyes and the arm. This is exactly the modulation required to convert an eye-centered visual target representation into an arm-centered representation.;Finally, to investigate reference frames, we recorded from PRR while monkeys planned and reached to multiple target locations from varying initial eye and arm positions. During the time of reach planning, different neurons employed different frames of reference; some represented target location in an eye-centered, and others in an arm-centered, frame of reference. Still some others used an intermediate representation. Our results show that PRR employs multiple coding schemes.