Daselaar S M, Veltman D J, Rombouts S A R B, Raaijmakers J G W, Jonker C
Institute for Research in Extramural Medicine, Vrije Universiteit Medical Center, Amsterdam, The Netherlands.
Brain. 2003 Jan;126(Pt 1):43-56. doi: 10.1093/brain/awg005.
Lesion studies have shown convincingly that the medial temporal lobes (MTL) and frontal lobes are critical to episodic memory. Ageing generally has been found to have a generally negative effect on episodic memory performance, which might relate to neurofunctional changes in the frontal and medial temporal brain regions. In the present study, we used functional MRI (fMRI) to investigate separately the contributions of encoding and retrieval to the age-related decline in memory. To this end, we compared brain activity patterns obtained during incidental encoding (pleasant/unpleasant judgements about nouns) and subsequent retrieval (recognition) in three groups: a group of young subjects, a group of elderly subjects showing reduced memory performance (ELD-RED), and a group of elderly subjects who still performed in the normal range (ELD-NORM). This allowed us to differentiate between age-related changes in brain activity that affect memory function and those that do not have an apparent effect on memory function, because they are found in both elderly groups. Contrary to previous imaging studies on this topic, we used (self-paced) event-related fMRI to control for differences in performance level across groups by including correct responses only. Comparing the encoding of successfully remembered items with baseline (press left/press right), the young subjects showed a significant increase in brain activation in the left anterior MTL compared with the ELD-RED but not the ELD-NORM subjects. Comparing correctly rejected items (retrieval attempt) with baseline, the ELD-RED group showed much increased overall activity throughout the brain compared with the other groups. However, when correctly recognized items (retrieval attempt + success) were compared directly with correctly rejected items (retrieval attempt), these differences were greatly reduced, revealing common activity in the left parietal, retrosplenial and left anterior prefrontal regions. Therefore, we conclude that the reduced performance in the ELD-RED group is likely to be due to MTL dysfunction during encoding. The differences observed during retrieval attempts may reflect strategic differences. The lack of differences observed in relation to retrieval success suggests that ageing does not affect the processes that support the actual recovery of information.
病灶研究已令人信服地表明，内侧颞叶（MTL）和额叶对情景记忆至关重要。一般而言，衰老被发现对情景记忆表现通常具有负面影响，这可能与额叶和内侧颞叶脑区的神经功能变化有关。在本研究中，我们使用功能磁共振成像（fMRI）分别研究编码和检索对与年龄相关的记忆衰退的影响。为此，我们比较了三组在偶然编码（对名词的愉快/不愉快判断）和随后检索（识别）过程中获得的大脑活动模式：一组年轻受试者、一组记忆表现下降的老年受试者（ELD - RED）和一组仍在正常范围内表现的老年受试者（ELD - NORM）。这使我们能够区分影响记忆功能的与年龄相关的大脑活动变化和那些对记忆功能没有明显影响的变化，因为它们在两个老年组中都存在。与之前关于该主题的成像研究相反，我们使用（自定节奏的）事件相关fMRI，仅纳入正确反应来控制各组表现水平的差异。将成功记住的项目的编码与基线（按左/按右）进行比较，与ELD - RED组相比，年轻受试者在左前MTL的大脑激活显著增加，但与ELD - NORM组相比则没有。将正确拒绝的项目（检索尝试）与基线进行比较，与其他组相比，ELD - RED组在整个大脑中的总体活动大幅增加。然而，当将正确识别的项目（检索尝试 + 成功）直接与正确拒绝的项目（检索尝试）进行比较时，这些差异大大减少，揭示了左顶叶、压后皮质和左前额叶前部区域的共同活动。因此，我们得出结论，ELD - RED组表现下降可能是由于编码过程中MTL功能障碍所致。在检索尝试期间观察到的差异可能反映了策略差异。在检索成功方面未观察到差异表明，衰老不会影响支持信息实际恢复的过程。
