Muhle-Karbe Paul S, Duncan John, De Baene Wouter, Mitchell Daniel J, Brass Marcel
Department of Experimental Psychology, Ghent University, Gent, Belgium.
Center for Cognitive Neuroscience, Duke University, Durham, USA.
Cereb Cortex. 2017 Mar 1;27(3):1891-1905. doi: 10.1093/cercor/bhw032.
Task preparation has traditionally been thought to rely upon persistent representations of instructions that permit their execution after delays. Accumulating evidence suggests, however, that accurate retention of task knowledge can be insufficient for successful performance. Here, we hypothesized that instructed facts would be organized into a task set; a temporary coding scheme that proactively tunes sensorimotor pathways according to instructions to enable highly efficient "reflex-like" performance. We devised a paradigm requiring either implementation or memorization of novel stimulus-response mapping instructions, and used multivoxel pattern analysis of neuroimaging data to compare neural coding of instructions during the pretarget phase. Although participants could retain instructions under both demands, we observed striking differences in their representation. To-be-memorized instructions could only be decoded from mid-occipital and posterior parietal cortices, consistent with previous work on visual short-term memory storage. In contrast, to-be-implemented instructions could also be decoded from frontoparietal "multiple-demand" regions, and dedicated visual areas, implicated in processing instructed stimuli. Neural specificity in the latter moreover correlated with performance speed only when instructions were prepared, likely reflecting the preconfiguration of instructed decision circuits. Together, these data illuminate how the brain proactively optimizes performance, and help dissociate neural mechanisms supporting task control and short-term memory storage.
传统上认为任务准备依赖于指令的持续表征，以便在延迟后执行这些指令。然而，越来越多的证据表明，准确保留任务知识对于成功执行任务可能并不足够。在此，我们假设所指示的事实会被组织成一个任务集；这是一种临时编码方案，根据指令主动调整感觉运动通路，以实现高效的“反射样”表现。我们设计了一种范式，要求对新的刺激 - 反应映射指令进行执行或记忆，并使用神经成像数据的多体素模式分析来比较目标前阶段指令的神经编码。尽管参与者在两种要求下都能保留指令，但我们观察到它们在表征上存在显著差异。待记忆的指令只能从中枕叶和顶叶后部皮质解码，这与之前关于视觉短期记忆存储的研究一致。相比之下，待执行的指令还可以从额顶叶“多需求”区域以及专门的视觉区域解码，这些区域与处理指示刺激有关。此外，只有在准备指令时，后者的神经特异性才与表现速度相关，这可能反映了指示决策电路的预配置。总之，这些数据揭示了大脑如何主动优化表现，并有助于区分支持任务控制和短期记忆存储的神经机制。
