中年失憶不必擔心?


  【24drs.com】一篇新的影像學研究認為,中年失憶反映的可能是腦部在形成記憶和檢索記憶時的某種資訊類型轉變,而不是認知功能下降。
  
  加拿大蒙特婁McGill大學Douglas腦部影像中心研究人員發現,記憶任務中,青壯年的視覺皮層活化比中老年人增加;相對的,中老年人的前額葉皮層比較活化。
  
  主要研究者、Douglas腦部影像中心主任Natasha Rajah博士表示,當你首次遇見某人,年輕人會注意在何時何地遇到這個人,他們可以記住這個資訊。
  
  Rajah博士指出,但是,中老年人會比較注意他們遇到的人的社會情感關聯─他們愉快嗎,他們是否提到他們認識的其他人等等─有關注意的重點上的這個差異,對他們記住更多客觀特徵造成負面影響。
  
  這篇研究線上發表於6月12日NeuroImage期刊。
  
  眾多研究顯示,與失智有關的腦部變化在症狀發生的幾十年前就開始,因此,當前記憶研究的一個關鍵問題是,關注哪些變化是正常的,哪些不是。
  
  Rajah博士在一份新聞稿中表示,我們對健康老化之中年人的改變、這些改變對老年生活的關聯所知有限,我們的研究目標即是在於解決這個議題。
  
  此次研究,研究人員共招募了112名19-76歲成人,這些研究對象沒有神經或心理疾病史,也沒有阿茲海默氏症家族史。
  
  共兩次測試,第一次時,參與者完成了多個神經心理學評估,包括迷你國際神經精神會談工具以及貝克憂鬱量表。接著,參與者在一系列的實驗性操作期間進行功能性MRI (fMRI),他們在這些操作時必須編碼和檢索臉部的空間和時間詳情。
  
  在檢索時,參與者被要求回憶某一特定的臉部出現在螢幕上的位置─左或右─或它何時出現—最近一次或近期最少。接著用fMRI掃描分析以確認,在回憶臉部詳情時,腦中的哪個區域被活化。
  
  fMRI掃描的分析發現,當年輕人完成回憶任務時,他們的視覺皮層被活化。
  
  Rajah博士表示,這表示,青壯年真正注意使他們決定的感性細節。
  
  當進行相同的回憶任務時,中老年研究對象並沒有相同程度的視覺皮層活化,而是在編碼時,內側前額葉皮質有較多的活動;檢索時,海馬旁皮質較多活動,這些區域涉及處理與反思活動更相關的訊息。
  
  Rajah博士表示,換句話說,青壯年和年長者在空間與時間處理上的差異,可能反映出不同年齡層的成年人在判斷哪些是重要資訊上的差異。
  
  這種解釋獲得一個事實支持,編碼任務過程中,參與者被要求,不僅要以客觀的方式進行外部資訊編碼,還要記住這些臉孔出現時是愉悅的還是中性的。
  
  Rajah博士表示,我們認為,中年人和老年人可能比較會涉及作出愉悅感之判斷,這些判斷可能會在記憶任務中業已擬定,即使我們明確指示參與者,記憶任務只和臉部的空間與時間關聯資訊有關。
  
  Rajah博士也認為,透過學習更專注於過程中出現的外部客觀資訊,年長者也許可以提高他們的回憶能力。
  
  例如,曾有文獻提出,正念可改善認知功能,因為它教人活在當下且顧及經驗的客觀性質,而非反覆思考與侷限於自己的內心。
  
  現在,需要一篇縱向研究,以確認中年和老年人的大腦編碼和檢索回憶觀察到的差異,是否反映腦部功能衰退,或是反映年長者在任何經驗類型的注意重點。
  
  資料來源:http://www.24drs.com/
  
  Native link:Midlife Memory Lapses No Cause for Concern?

Midlife Memory Lapses No Cause for Concern?

By Pam Harrison
Medscape Medical News

Midlife memory lapses may reflect a shift in the type of information the brain focuses on during memory formation and retrieval, rather than a decline in cognitive function, a new imaging study suggests.

Investigators at Douglas Brain Imaging Centre, McGill University, Montreal, Canada, found that during a memory task, activation of the visual cortex was increased in young adults in comparison with middle-aged and older adults.

In contrast, in middle-aged and older adults, activation was greater in the prefrontal cortex.

"When you meet someone for the first time, it is likely that young adults are paying attention to where and when they met this person, and they can remember this information," principal investigator Natasha Rajah, PhD, director, Douglas Brain Imaging Centre, told Medscape Medical News.

"But middle-aged and older adults focus more on the social-emotional relevance of the person they met ─ were they pleasant, whether they reminded them of other people they know, and so on ─ and this change in focus negatively impacts their ability to remember more objective features," Dr Rajah added.

The study was published online June 12 in NeuroImage.

What's Normal, What's Not?

Numerous studies have shown that brain changes associated with dementia begin decades before the onset of symptoms. Therefore, a key question in current memory research concerns which changes are normal and which are not.

"We know little about what happens at midlife in healthy aging and how this relates to findings in late life. Our research was aimed at addressing this issue," Dr Rajah said in a release.

For the study, investigators recruited 112 adults aged 19 to 76 years. The participants had no history of neurologic or psychological illness, nor did they have a family history of Alzheimer's disease.

During the first of two test sessions, participants completed multiple neuropsychological assessments, including the Mini-International Neuropsychiatric Interview and the Beck Depression Inventory.

Participants then underwent functional MRI (fMRI) during a series of experimental runs in which they had to encode and retrieve spatial and temporal details of faces.

During retrieval, participants were asked to recall where a particular face appeared on a screen ─ left or right ─ or when it appeared — most recently or least recently. fMRI scans were then analyzed to identify which areas of the brain were activated during recall of facial details.

Analyses of the fMRI scans revealed that the visual cortex was activated in young adults as they completed the recall task.

"This suggests that young adults are really paying attention to perceptual details to make their decisions," said Dr Rajah.

Mindfulness May Help

Middle-aged and older participants did not exhibit the same level of visual cortex activation when engaged in the same recall task but rather showed more activity in the medial prefrontal cortex during encoding and in the parahippocampal cortex during retrieval. These regions are involved in processing information that has more to do with introspective activity.

In other words, the differences in spatial and temporal processing observed between young adults and older participants may reflect a difference in what adults judge to be important information as they age, said Dr Rajah.

This interpretation is supported by the fact that during the encoding task, participants were asked not only to encode external information in an objective way but also to register whether the face being presented was pleasant or neutral.

"We think middle-aged and older adults may be more engaged in making 'pleasantness' judgments, and these judgments may have been elaborated upon during the memory task, even though we explicitly instructed participants that the memory task was only about spatial and temporal contextual information of the faces," said Dr Rajah.

Dr Rajah also suggested that older adults might be able to improve their recall abilities by learning to focus more on external objective information during encounters.

It has been suggested, for example, that mindfulness may improve cognitive function because it teaches individuals to be "present in the moment" and to attend to the objective nature of the experience instead of ruminating and being caught up in their own inner world.

A longitudinal study is now needed to determine whether the observed differences in the way middle-aged and older brains encode and retrieve memories is a reflection of functional brain decline or a reflection of what older adults pay attention to during any type of experience.

Dr Rajah has disclosed no relevant financial relationships.

Neuroimage. Published online June 12, 2016.

    
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