• Ying Chen, Simona Monaco, Patrick Byrne, Xiaogang Yan, Denise Y P Henriques, and J Douglas Crawford.
• Center for Vision Research and Departments of Psychology, Biology, and Kinesiology and Health Science, York University, Toronto, Ontario M3J 1P3, Canada, and Canadian Action and Perception Network, York University, Toronto, Ontario M3J 1P3, Canada liuc@yorku.ca.
• J. Neurosci. 2014 Sep 10; 34 (37): 12515-26.

AbstractThe location of a remembered reach target can be encoded in egocentric and/or allocentric reference frames. Cortical mechanisms for egocentric reach are relatively well described, but the corresponding allocentric representations are essentially unknown. Here, we used an event-related fMRI design to distinguish human brain areas involved in these two types of representation. Our paradigm consisted of three tasks with identical stimulus display but different instructions: egocentric reach (remember absolute target location), allocentric reach (remember target location relative to a visual landmark), and a nonspatial control, color report (report color of target). During the delay phase (when only target location was specified), the egocentric and allocentric tasks elicited widely overlapping regions of cortical activity (relative to the control), but with higher activation in parietofrontal cortex for egocentric task and higher activation in early visual cortex for allocentric tasks. In addition, egocentric directional selectivity (target relative to gaze) was observed in the superior occipital gyrus and the inferior occipital gyrus, whereas allocentric directional selectivity (target relative to a visual landmark) was observed in the inferior temporal gyrus and inferior occipital gyrus. During the response phase (after movement direction had been specified either by reappearance of the visual landmark or a pro-/anti-reach instruction), the parietofrontal network resumed egocentric directional selectivity, showing higher activation for contralateral than ipsilateral reaches. These results show that allocentric and egocentric reach mechanisms use partially overlapping but different cortical substrates and that directional specification is different for target memory versus reach response. Copyright © 2014 the authors 0270-6474/14/3412515-12$15.00/0.

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