Dataset for: Neural Substrates for Allocentric-to-Egocentric Conversion of Remembered Reach Targets in Humans

Targets for goal-directed action can be encoded in allocentric coordinates (relative to another visual landmark), but it is not known how these are converted into egocentric commands for action. Here, we investigated this using a slow event-related fMRI paradigm, based on our previous behavioral finding that the Allocentric to Egocentric (Allo-Ego) conversion for reach is done at the first possible opportunity. Participants were asked to remember (and eventually reach toward) the location of a briefly presented target relative to another visual landmark. After a 1st memory delay, participants were forewarned by a verbal instruction if the landmark would reappear at the same location, (potentially allowing them to plan a reach following the auditory cue before the 2nd delay), or at a different location where they had to wait for the final landmark to be presented before response, and then reach toward the remembered target location. As predicted, participants showed landmark-centered directional selectivity in occipital-temporal cortex during the first memory delay, only developed egocentric directional selectivity in occipital-parietal cortex during the second delay for the “Same cue” task, and during response for the “Different cue” task. We then compared cortical activation between these two tasks at the times when the Allo-Ego conversion occurred, and found common activation in right precuneus, right pre-supplementary area and bilateral dorsal premotor cortex. These results confirm that the brain converts allocentric codes to egocentric plans at the first possible opportunity, and identify the four most likely candidate sites specific to the Allo-Ego transformation for reaches.

目标导向动作的目标可通过以客体为中心的坐标系（allocentric coordinates）进行编码，即相对于另一视觉地标，但目前尚不明确大脑如何将此类编码转化为用于动作的自我中心指令（egocentric commands）。本研究基于此前的行为学发现——伸手动作的以客体为中心到自我中心（Allocentric to Egocentric，简称Allo-Ego）转换会在首个可行时机完成——采用慢事件相关功能磁共振成像（fMRI）范式对此展开探究。实验要求被试记住短暂呈现的目标相对于某一视觉地标的位置，并最终伸手指向该目标的位置。在首个记忆延迟阶段结束后，若地标将在原位置重现，被试会收到口头提示，这可使他们在第二个延迟阶段前借助该听觉线索规划伸手动作；若地标将出现在其他位置，被试则需等待最终地标呈现后再做出反应，随后伸手指向记忆中的目标位置。正如实验预期，被试在首个记忆延迟阶段的枕叶-颞叶皮层（occipital-temporal cortex）中表现出以地标为中心的方向选择性；而在"同地标提示"任务的第二个延迟阶段，以及"不同地标提示"任务的反应阶段，枕叶-顶叶皮层（occipital-parietal cortex）才逐渐出现自我中心的方向选择性。随后，我们在Allo-Ego转换发生的时段对两项任务的皮层激活模式进行对比，发现右侧楔前叶（right precuneus）、右侧前补充运动区（right pre-supplementary area）以及双侧背侧运动前皮层（bilateral dorsal premotor cortex）存在共同激活。上述结果证实，大脑会在首个可行时机完成以客体为中心的编码到自我中心动作计划的转换，并明确了4处最有可能的伸手动作Allo-Ego转换特异性候选脑区。