Neuroscience Research Australia, Barker Street, Randwick, Sydney, NSW 2031, Australia.
Neuropsychologia. 2012 Dec;50(14):3488-95. doi: 10.1016/j.neuropsychologia.2012.09.012. Epub 2012 Sep 14.
Semantic dementia (SD) is a progressive neurodegenerative disorder characterised by the amodal loss of semantic knowledge in the context of relatively preserved recent episodic memory. Recent studies have demonstrated that despite relatively intact episodic memory the capacity for future simulation in SD is profoundly impaired, resulting in an asymmetric profile where past retrieval is significantly better than future simulation (referred to as a past>future effect). Here, we sought to identify the origins of this asymmetric profile by conducting a fine-grained analysis of the contextual details provided during past retrieval and future simulation in SD. Participants with SD (n=14), Alzheimer's disease (n=11), and healthy controls (n=14) had previously completed an experimental past-future interview in which they generated three past events from the previous year, and three future events in the next year, and provided subjective qualitative ratings of vividness, emotional valence, emotional intensity, task difficulty, and personal significance for each event described. Our results confirmed the striking impairment for future simulation in SD, despite a relative preservation of past episodic retrieval. Examination of the contextual details provided for past memories and future simulations revealed significant impairments irrespective of contextual detail type for future simulations in SD, and demonstrated that the future thinking deficit in this cohort was driven by a marked decline in the provision of internal (episodic) event details. In contrast with this past>future effect for internal event details, SD patients displayed a future>past effect for external (non-episodic) event details. Analyses of the qualitative ratings provided for past and future events indicated that SD patients' phenomenological experience did not differ between temporal conditions. Our findings underscore the fact that successful extraction of episodic elements from the past is not sufficient for the generation of novel future simulations in SD. The notable disconnect between objective task performance and patients' subjective experience during future simulation likely reflects the tendency of SD patients to recast entire past events into the future condition. Accordingly, the familiarity of the recapitulated details results in similar ratings of vividness and emotionality across temporal conditions, despite marked differences in the richness of contextual details as the patient moves from the past to the future.
语义痴呆症（SD）是一种进行性神经退行性疾病，其特征是在相对保留近期情景记忆的情况下，出现语义知识的非模态丧失。最近的研究表明，尽管情景记忆相对完整，但 SD 患者的未来模拟能力受到严重损害，导致不对称的模式，即过去检索明显优于未来模拟（称为过去>未来效应）。在这里，我们通过对 SD 患者过去检索和未来模拟过程中提供的上下文细节进行精细分析，试图确定这种不对称模式的起源。14 名 SD 患者、11 名阿尔茨海默病患者和 14 名健康对照组参与者之前完成了一项实验性的过去-未来访谈，他们从过去一年中生成了三个过去事件，以及下一年中的三个未来事件，并对每个事件的生动性、情绪效价、情绪强度、任务难度和个人意义进行了主观的定性评价。我们的结果证实，尽管 SD 患者的过去情景记忆相对保留，但未来模拟能力严重受损。对过去记忆和未来模拟提供的上下文细节的检查表明，SD 患者的未来模拟存在显著的障碍，无论上下文细节类型如何，并且表明该队列的未来思维缺陷是由于内部（情景）事件细节的明显下降所致。与这种内部事件细节的过去>未来效应相反，SD 患者对外部（非情景）事件细节表现出未来>过去效应。对过去和未来事件提供的定性评价的分析表明，SD 患者在时间条件下的现象体验没有差异。我们的发现强调了这样一个事实，即从过去成功提取情景元素不足以在 SD 中生成新的未来模拟。在未来模拟期间，客观任务表现与患者的主观体验之间明显脱节，可能反映了 SD 患者将整个过去事件重构到未来状态的趋势。因此，尽管在患者从过去移动到未来时，上下文细节的丰富度存在明显差异，但重新叙述的细节的熟悉度导致在时间条件下产生相似的生动性和情感性评价。
