by 贾香莲 | 2015-07-07
二次世界大战期间，James Hilton编写的小说 《Random Harvest》，被搬上荧屏，影片中男主人公罗纳德因其选择性遗忘症和女主人葛莉亚相识相恋，而此后也因其选择性遗忘症让这对有情人体会了“我在你面前，你却不认识我”的心酸。此后，失忆-找回记忆这个更成为演艺界一个重要题材，也侧面反应了大众对“记忆”的关注。在脑科学研究如火如荼的今天，关于巩固记忆避免遗忘有大量的文献报道。其实在现实生活中，对于创伤后应激性障碍（PTSD）患者而言，创伤的记忆困扰他们的正常生活，这种情况下，“遗忘”也同样重要。
2015年3月16日，哥伦比亚大学的Michacl.C.Anderson 研究组发表在《Nature Neuroscience》上的一篇文章指出，新记忆的形成不但能直接擦除旧的记忆；同时在记忆提取时，能竞争性地抑制同一场景中干扰记忆提取的经历，间接地改变曾经记忆。研究人员将功能磁共振技术和行为学技术结合，开发出基于模板的模式追踪方法，该方法可以量化单个记忆追踪中大脑特定区域的活动状态。他们发现利用同一单词作为线索，让被试者记忆两个（目标性和竞争性）和线索相关的物体，之后在记忆提取时候，故意引导被试者回忆目标物体，随着记忆提取次数的增加，目的物体正确概率不断升高，而竞争性物体正确概率逐渐下降，即被试者在记忆提取时记住了目的物体，而竞争性物体逐渐被遗忘。在记忆提取过程中，研究人员用功能磁共振技术记录了被试者大脑活动状态，结果发现在竞争性遗忘过程中，腹外侧前额叶皮层活动被抑制。
题目: Retrieval induces adaptive forgetting of competing memories via cortical pattern suppression
摘要: Remembering a past experience can,surprisingly, cause forgetting. Forgetting arises when other competing tracesinterfere withretrieval and inhibitory control mechanisms are engaged to suppress thedistraction they cause. This form of forgetting is considered to be adaptive because it reducesfuture interference. The effect of this proposed inhibition process oncompeting memories has, however,never been observed, as behavioral methods are ‘blind’ to retrieval dynamicsand neuroimaging methods havenot isolated retrieval of individual memories. We developed a canonicaltemplate tracking method to quantify the activation state of individual target memories and competitors duringretrieval. This method revealed that repeatedly retrieving target memories suppressed cortical patterns unique tocompetitors. Pattern suppression was related to engagement of prefrontal regions that have beenimplicated in resolving retrieval competition and, critically, predicted laterforgetting. Thus, our findingsdemonstrate a cortical pattern suppression mechanism through which rememberingadaptively shapes which aspectsof our past remain accessible
题目: Failing to Forget: Inhibitory-Control DeficitsCompromise Memory Suppression in Posttraumatic Stress Disorder
摘要: Most people have experienced distressing events that they would ratherforget. Although memories of such events become less intrusive with time forthe majority of people, those with posttraumatic stress disorder (PTSD) areafflicted by vivid, recurrent memories of their trauma. Often triggered byreminders in the daily environment, these memories can cause severe distressand impairment. We propose that difficulties with intrusive memories in PTSDarise in part from a deficit in engaging inhibitory control to suppressepisodic retrieval. We tested this hypothesis by adapting the think/no-thinkparadigm to investigate voluntary memory suppression of aversive scenes cued bynaturalistic reminders. Retrieval suppression was compromised significantly inPTSD patients, compared with trauma-exposed control participants. Furthermore,patients with the largest deficits in suppression-induced forgetting were alsothose with the most severe PTSD symptoms. These results raise the possibilitythat prefrontal mechanisms supporting inhibitory control over memory areimpaired in PTSD
题目:Suppressing unwanted memories by executive control
摘要: Freud proposed that unwanted memories can beforgotten by pushing them into the unconscious, a process called repression.The existence of repression has remained controversial for more than a century,in part because of its strong coupling with trauma, and the ethical andpractical difficulties of studying such processes in controlled experiments.However, behavioural and neurobiological research on memory and attention showsthat people have executive control processes directed at minimizing perceptual distraction,overcoming interference during short and long-term memory tasks and stopping stronghabitual responses to stimuli . Here we show thatthese mechanisms can be recruited to prevent unwanted declarative memories fromentering awareness, and that this cognitive act has enduring consequences forthe rejected memories. When people encounter cues that remind them of anunwanted memory and they consistently try to prevent awareness of it, the laterrecall of the rejected memory becomes more difficult. The forgetting increaseswith the number of times the memory is avoided, resists incentives for accuraterecall and is caused by processes that suppress the memory itself. Theseresults show that executive control processes not uniquely tied to trauma may providea viable model for repression.
题目: The Prefrontal Cortex Achieves Inhibitory Control by Facilitating Sub-corticalMotor Pathway Connectivity
摘要: Communicationbetween the prefrontal cortex and subcortical nucleiunderpins the control and inhibition ofbehavior. However, the interactionsin such pathways remaincontroversial. Using a stop-signal response inhibition task and functionalimaging with analysis of effective connectivity,we show that the lateral prefrontal cortex influences the strength of communicationbetween regions in the frontostriatal motor system. We compared 20generative models that represented alternative interactions between the inferior frontal gyrus, pre-supplementarymotor area (preSMA),subthalamic nucleus (STN), and primary motor cortex duringresponse inhibition. Bayesian model selection revealed that during successfulresponse inhibition, the inferiorfrontal gyrus modulates an excitatory influence of the preSMA on the STN, thereby amplifying the downstreampolysynaptic inhibition from theSTNto the motor cortex. Critically, the strengthof the interaction betweenpreSMA and STN, and the degreeof modulation by the inferior frontal gyrus,predicted individual differences in participants\' stopping performance(stop-signal reaction time). We thenused diffusion-weighted imaging with tractography to assess white matterstructure inthe pathways connecting these three regions. The mean diffusivity in tractsbetween preSMA and the STN,and between the inferiorfrontal gyrus and STN, also predicted individual differences in stoppingefficiency. Finally, we found that white matter structure in the tract between preSMA and STNcorrelated with effective connectivity of thesame pathway, providing importantcross-modal validation of the effective connectivity measures. Together, theresults demonstrate the network dynamics and modulatory role of the prefrontal cortex thatunderpin individual differences in inhibitory control.