Supplementary Material for: Decline in Search Speed and Verbal Memory Over 26 Years of Midlife in a British Birth Cohort

<b><i>Background:</i></b> Cognitive capabilities change in later life, although their onset and rate of decline, and how they are shaped by lifetime socioeconomic position, childhood cognition and adult health status are all unclear. <b><i>Methods:</i></b> From the Medical Research Council National Survey of Health and Development, we analysed 3,192 participants undergoing one or more cognitive assessments at ages 43, 53, 60–64 and 69. Linear mixed models described cognitive trajectories, adjusting for factors across the life course. <b><i>Results:</i></b> For both search speed and verbal memory, better performance at age 43 (the intercept) was associated with higher paternal and own education, childhood cognition, and adult occupational class. For search speed, the trajectory was best described as a quadratic function (decline of 45.6 letters/5-years + 4.6 letters). Verbal memory showed a linear decline of 0.20 words/5-years between ages 43 and 60 and a steeper linear decline of 0.95 words/5-years between ages 60 and 69. Decline in verbal memory in the latter period was steeper in those with higher educational achievements at age 26 (additional 0.28 words/5-years for highest attainment). <b><i>Conclusions:</i></b> Decline in verbal memory and search speed across midlife is evident, though with different non-linear trajectories. By implication, pathways to cognitive impairment and dementia in older age may have their origins in this period.

**背景**：认知能力在晚年阶段会发生改变，但其起始时间、衰退速率，以及终生社会经济地位、儿童期认知水平与成年健康状况如何塑造这些变化，目前尚无定论。
**方法**：本研究依托医学研究理事会全国健康与发展调查（Medical Research Council National Survey of Health and Development）数据集，纳入3192名参与者进行分析，上述人群分别在43岁、53岁、60~64岁及69岁时接受了1次及以上认知功能评估。本研究采用线性混合模型刻画认知轨迹，并对生命历程各阶段的混杂变量进行校正。
**结果**：在搜索速度与言语记忆两项指标中，43岁时（截距项）的认知表现越好，其父亲受教育程度、自身受教育程度、儿童期认知水平以及成年职业阶层往往越高。就搜索速度而言，其认知轨迹最优拟合为二次函数，每5年的衰退幅度为45.6个字母，叠加4.6个字母的二次项修正。言语记忆在43岁至60岁区间内呈现每5年0.20个单词的线性衰退，而在60岁至69岁区间内的衰退幅度更为显著，达到每5年0.95个单词。在60岁至69岁这一后期阶段，26岁时受教育程度更高的群体，其言语记忆衰退速率更快：最高受教育水平群体的衰退速率较其他群体额外增加0.28个单词/每5年。
**结论**：中年阶段的言语记忆与搜索速度衰退现象较为显著，但二者呈现出不同的非线性轨迹。由此提示，老年阶段认知损害与痴呆的发病通路，可能起源于中年这一时期。