Department of Psychology, University of California, Riverside, 900 University Avenue, Riverside, CA 92521, USA.
Department of Psychology, St. Olaf College, 1520 St. Olaf Avenue, Northfield, MN 55057, USA.
Behav Brain Res. 2021 Jan 15;397:112950. doi: 10.1016/j.bbr.2020.112950. Epub 2020 Oct 2.
Older adults are impaired at implicit associative learning (IAL), or the learning of relationships between stimuli in the environment without conscious awareness. These age effects have been attributed to differential engagement of the basal ganglia (e.g. caudate, globus pallidus) and hippocampus throughout learning. However, no studies have examined gray matter diffusion relations with IAL, which can reveal microstructural properties that vary with age and contribute to learning. In this study, young (18-29 years) and older (65-87 years) adults completed the Triplet Learning Task, in which participants implicitly learn that the location of cues predict the target location on some trials (high frequency triplets). Diffusion imaging was also acquired and multicompartment diffusion metrics were calculated using neurite orientation dispersion and density imaging (NODDI). As expected, results revealed age deficits in IAL (smaller differences in performance to high versus low frequency triplets in the late learning stage) and age-related differences in basal ganglia and hippocampus free, hindered, and restricted diffusion. Significant correlations were seen between restricted caudate diffusion and early IAL and between hindered globus pallidus diffusion and late IAL, which were not moderated by age group. These findings indicate that individual differences in basal ganglia, but not hippocampal, gray matter microstructure contribute to learning, independent of age, further supporting basal ganglia involvement in IAL.
老年人在隐性联想学习（IAL）方面存在障碍，即无法在无意识的情况下学习环境刺激之间的关系。这些年龄效应归因于在学习过程中基底神经节（例如尾状核、苍白球）和海马体的不同参与。然而，目前还没有研究检查与 IAL 相关的灰质扩散关系，因为这种关系可以揭示出随年龄变化的微观结构特性，并有助于学习。在这项研究中，年轻（18-29 岁）和年长（65-87 岁）成年人完成了三联体学习任务，在该任务中，参与者在某些试次中隐性地学习到线索的位置预测目标位置（高频三联体）。还采集了扩散成像，并使用神经丝取向弥散和密度成像（NODDI）计算了多室扩散指标。正如预期的那样，结果显示出 IAL 的年龄缺陷（在后期学习阶段，高频与低频三联体之间的表现差异较小），以及与基底神经节和海马体相关的自由扩散、受阻扩散和受限扩散的年龄差异。在受限尾状核扩散与早期 IAL 之间，以及受阻苍白球扩散与晚期 IAL 之间，观察到显著的相关性，这些相关性不受年龄组的调节。这些发现表明，个体基底神经节，而不是海马体的灰质微观结构差异，有助于学习，与年龄无关，进一步支持基底神经节参与 IAL。
