Mok Leh Woon, Thomas Kathleen M, Lungu Ovidiu V, Overmier J Bruce
Department of Psychology, University of Minnesota, Twin Cities, Minnesota 55455, USA.
Brain Res. 2009 Apr 10;1265:111-27. doi: 10.1016/j.brainres.2008.12.072. Epub 2009 Jan 15.
In conditional discriminative choice learning, one learns the relations between discriminative/cue stimuli, associated choices, and their outcomes. When each correct cue-choice occurrence is followed by a cue-unique trial outcome (differential outcomes, DO, procedure), learning is faster and more accurate than when all correct cue-choice occurrences are followed by a common outcome (CO procedure)--differential outcomes effect (DOE). Superior DO performance is theorized to be mediated by the additional learning of cue-unique outcome expectations that "enrich" the prospective code available over the delay between cue and choice. We anticipated that such learned expectations comprise representations of expected outcomes. Here, we conducted an event-related functional MR imaging (fMRI) analysis of healthy adults who trained concurrently in two difficult but similar perceptual discrimination tasks under DO and CO procedures, respectively, and displayed the DOE. Control participants performed related tasks that differentially biased them towards delay-period retrospection versus prospection. Indeed, when differential outcomes were sensory-perceptual events (visual vs. auditory), delay-period expectations were experienced as sensory-specific imagery of the respectively expected outcome content, generated by sensory-specific cortices. Visual-specific imagery additionally activated stimulus-specific representations in prefrontal, lateral and medial frontal, fusiform and cerebellar regions, whereas auditory-specific imagery recruited claustrum/insula. Posterior parietal cortex (PPC), BA 39, was non-modality specific in mediating delay-period cue-unique outcome expectations. Greater hippocampal involvement in retrospection than prospection contrasted against the PPC's role in prospection. Time course analyses of hippocampal versus PPC responses suggest the DOE derives from an earlier transition from retrospection to prospection, which taps into long-term associative memory--more enduring.
在条件性辨别选择学习中，个体学习辨别性/线索刺激、相关选择及其结果之间的关系。当每一次正确的线索 - 选择出现后都跟随一个线索独特的试验结果（差异结果，DO，程序）时，学习比所有正确的线索 - 选择出现后都跟随一个共同结果（CO程序）时更快且更准确——差异结果效应（DOE）。理论上，优越的DO表现是由线索独特结果期望的额外学习介导的，这些期望“丰富”了线索与选择之间延迟期间可用的前瞻性编码。我们预期这种习得的期望包含预期结果的表征。在这里，我们对健康成年人进行了一项事件相关功能磁共振成像（fMRI）分析，这些成年人分别在DO和CO程序下同时训练两个困难但相似的知觉辨别任务，并表现出DOE。对照组参与者执行相关任务，这些任务使他们在延迟期的回顾与前瞻方面存在差异偏向。实际上，当差异结果是感觉 - 知觉事件（视觉与听觉）时，延迟期期望被体验为分别预期结果内容的感觉特异性意象，由感觉特异性皮层产生。视觉特异性意象还额外激活了前额叶、外侧和内侧额叶、梭状回和小脑区域的刺激特异性表征，而听觉特异性意象则激活了屏状核/脑岛。顶叶后皮质（PPC），BA 39，在介导延迟期线索独特结果期望方面是非模态特异性的。海马在回顾中的参与程度高于前瞻，这与PPC在前瞻中的作用形成对比。海马与PPC反应的时间进程分析表明，DOE源于从回顾到前瞻的更早转变，这利用了长期联想记忆——更持久。
