Aging brains blend memories together instead of just forgetting them
Aging brains blend memories together instead of just forgetting them
老化的大脑会将记忆混淆在一起，而非仅仅是遗忘
(Credit: © Aryazu - stock.adobe.com) In a Nutshell: Memory accuracy for pairing faces with objects and scenes dropped sharply after young adulthood, with middle-aged and older adults scoring similarly to each other rather than declining in a steady line. Brain activity patterns that helped younger adults remember accurately were linked, in older adults, to more mix-up errors that crossed between entirely different categories of items, such as mistaking a scene for an object. Neither brain shrinkage nor attention differences fully explained why older adults’ brains showed this shift toward blended, less precise memories. （图片来源：© Aryazu - stock.adobe.com）简而言之：在成年早期之后，将人脸与物体或场景进行配对的记忆准确度急剧下降，中年人和老年人的得分相近，而非呈现线性下降。在年轻人中，有助于准确记忆的大脑活动模式，在老年人身上却与更多的混淆错误相关联，这些错误跨越了完全不同的类别，例如将场景误认为是物体。无论是大脑萎缩还是注意力差异，都无法完全解释为什么老年人的大脑会出现这种向“混合且不精确”记忆转变的现象。
An older relative insists they left their keys with a particular grandchild, in a particular room, on a particular day, and gets every detail wrong except that keys were involved. That kind of confident mix-up may not be simple forgetfulness. New brain-imaging research suggests something odder is happening inside aging brains: the very system meant to lock memories into place may be blending them together instead. 一位年长的亲戚坚称他们把钥匙留给了某个孙辈，在某个房间，在某一天，结果除了“钥匙”这件事外，所有细节都记错了。这种自信的混淆可能不仅仅是简单的健忘。新的脑成像研究表明，老化的大脑内部正在发生更奇怪的事情：旨在锁定记忆的系统，可能反而正在将它们混合在一起。
A study published in Cerebral Cortex scanned the brains of adults aged 18 to 74 as they learned pairs of faces with objects and faces with scenes, rested, and then tried to recall the correct pairings. Researchers tracked activity patterns in the hippocampus, the brain’s memory hub, at three points: while learning, during a quiet rest afterward, and during the memory test itself. 发表在《大脑皮层》（Cerebral Cortex）上的一项研究对 18 至 74 岁的成年人进行了脑部扫描。受试者需要学习人脸与物体、人脸与场景的配对，在休息后尝试回忆正确的配对。研究人员在三个时间点追踪了大脑记忆中枢——海马体的活动模式：学习时、随后的安静休息时，以及记忆测试时。
The results turn a common assumption about memory loss on its head. Older brains may not simply hold onto memories more weakly. In some cases, they hold onto too much of the wrong thing, replaying scattered pieces of unrelated experiences and stitching them into false connections. 研究结果颠覆了关于记忆丧失的普遍假设。老年人的大脑可能并非仅仅是记忆力减弱。在某些情况下，他们保留了太多错误的信息，不断重播不相关经历的碎片，并将它们拼凑成错误的联系。
Younger adults in the study showed a clean pattern: the more closely their brain activity during recall matched their brain activity during learning, the better they performed on the memory test. That’s the brain doing what it’s supposed to do, replaying one specific memory faithfully. But among older adults, that same overlap in brain activity stopped predicting accuracy and instead predicted a very specific kind of mistake: confusing items across entirely different categories, like linking a face to a scene when it had actually been paired with an object. Their brains were retrieving too broadly rather than not at all. 研究中的年轻人表现出一种清晰的模式：回忆时的大脑活动与学习时的大脑活动匹配度越高，记忆测试的表现就越好。这是大脑在执行其应有的功能，即忠实地重现特定的记忆。但在老年人中，这种大脑活动的重叠不再预示准确性，反而预示了一种非常具体的错误：混淆完全不同类别的项目，例如将一张人脸与一个场景联系起来，而实际上它原本是与一个物体配对的。他们的大脑检索范围太广，而不是完全无法检索。
How Scientists Tested Aging Brains and Memory
科学家如何测试老化的大脑与记忆
Researchers recruited adults between 18 and 74 years old and eventually analyzed data from 61 participants after excluding some for excessive head movement during scanning or other issues. The final group included 17 younger adults (ages 18 to 30), 21 middle-aged adults (ages 50 to 60), and 23 older adults (ages 61 to 74). 研究人员招募了 18 至 74 岁的成年人，在排除了扫描过程中头部过度移动或其他问题的受试者后，最终分析了 61 名参与者的数据。最终组包括 17 名年轻人（18 至 30 岁）、21 名中年人（50 至 60 岁）和 23 名老年人（61 至 74 岁）。
Each participant lay in an MRI scanner and completed a multi-step memory task. First, they completed a resting scan, lying still with their eyes closed. Then came the learning phase, where participants saw a face paired with either an object or a scene and were asked to imagine that person interacting with the item, a trick meant to help the pairing stick. After rating how likely they were to remember each pair, participants rested again inside the scanner. 每位参与者躺在核磁共振扫描仪中，完成一项多步骤的记忆任务。首先是静息扫描，闭眼静卧。接着是学习阶段，参与者看到一张人脸与一个物体或场景配对，并被要求想象该人与该物品互动，这是一种旨在帮助记忆配对的技巧。在评估了对每组配对的记忆可能性后，参与者再次在扫描仪内休息。
Finally, they took a memory test in which a face appeared alongside four possible answers, two objects and two scenes, and had to pick the one that had actually been paired with that face during learning. Some wrong answers were close misses, like choosing the wrong object when the answer was an object, while others were far off, like choosing a scene when the answer was an object. 最后，他们参加了一项记忆测试：屏幕上出现一张人脸和四个可能的选项（两个物体和两个场景），他们必须选出在学习阶段与该人脸配对的正确选项。一些错误答案属于“险些选对”，例如在答案是物体时选错了物体；而另一些则偏差较大，例如在答案是物体时选成了场景。
To study what was happening in the brain, researchers created an activity fingerprint for the hippocampus during each of the three phases, then measured how closely those fingerprints matched one another. A close match between the learning fingerprint and the recall fingerprint may mean the brain is reactivating the original memory, though similar activity can also reflect similar thinking rather than the exact same memory playing back. A weak or scrambled match suggests the memory trace has shifted or broken down somehow. 为了研究大脑中发生的情况，研究人员为海马体在三个阶段中的每一个阶段都创建了“活动指纹”，然后测量这些指纹之间的匹配程度。学习指纹与回忆指纹之间的高度匹配可能意味着大脑正在重新激活原始记忆，尽管相似的活动也可能反映了相似的思维过程，而非完全相同的记忆重现。匹配度较弱或混乱则表明记忆痕迹已经发生了偏移或某种程度的损坏。
What Brain Scans Revealed About Aging and Memory
脑部扫描揭示了关于衰老与记忆的什么信息
Age predicted memory performance strongly. Younger participants correctly identified the right pairing far more often than middle-aged or older participants, while middle-aged and older adults performed similarly. Age didn’t reliably predict how often people forgot entirely or what kind of error they made when the data was viewed as one overall pattern. The real differences only showed up once researchers looked at how brain similarity connected to those errors. 年龄对记忆表现有很强的预测作用。年轻参与者正确识别配对的频率远高于中年或老年参与者，而中年人和老年人的表现相似。当将数据视为一个整体模式时，年龄并不能可靠地预测人们完全遗忘的频率或他们犯错的类型。真正的差异只有在研究人员观察大脑相似性如何与这些错误相关联时才显现出来。
That connection sits at the center of the paper. Similarity between learning-phase and recall-phase brain patterns was strongest overall compared with the other phase pairings, and higher learning-to-recall similarity predicted better memory across participants. But once researchers accounted for age, a split appeared. 这种联系是该论文的核心。与其它阶段配对相比，学习阶段和回忆阶段的大脑模式相似度整体最强，且较高的“学习-回忆”相似度预示着所有参与者都有更好的记忆表现。但一旦研究人员将年龄因素考虑在内，分歧就出现了。
Younger adults with strong learning-to-recall similarity remembered more and forgot less. Middle-aged adults showed a weaker version of that same benefit. Older adults showed almost no benefit. Instead, stronger similarity in their brain patterns was linked to more cross-category confusion errors, the kind where a person mixes up an object with a scene entirely rather than confusing two similar items within the same category. That link showed up across the different brain-pattern comparisons, not just the learning-to-recall one. 具有较强“学习-回忆”相似度的年轻人记得更多，遗忘更少。中年人表现出同样但较弱的益处。老年人几乎没有表现出这种益处。相反，他们大脑模式中更强的相似性与更多的“跨类别混淆错误”相关联，即一个人将物体与场景完全混淆，而不是在同一类别内混淆两个相似的项目。这种联系出现在不同的大脑模式比较中，而不仅仅是在“学习-回忆”的比较中。
Researchers then tried to figure out why. Could it be brain shrinkage? Hippocampal volume did decline with age and was loosely tied to one phase of brain-pattern similarity, but accounting for volume didn’t erase the odd pattern in older adults. Could it be baseline differences in how organized the hippocampus was before learning even started? That baseline organization explained some of the age-related decline in overall accuracy, but not the category-confusion errors. Could it be attention problems, since old… 研究人员随后试图找出原因。是大脑萎缩吗？海马体体积确实随年龄增长而下降，并与某一阶段的大脑模式相似度有微弱联系，但考虑体积因素后，并没有消除老年人身上那种奇怪的模式。是学习开始前海马体组织方式的基线差异吗？这种基线组织解释了部分与年龄相关的整体准确度下降，但无法解释类别混淆错误。是注意力问题吗，因为老年人……