老年人如果夠幸運，便有望避免阿爾茨海默氏癥造成的恐怖影響,，這種疾病的典型特征便是記憶力和其他認知能力的顯著下降。迄今為止,，對于這種頑癥的發(fā)病機理人們知之甚少,，但一項新的研究表明,，認知水平的下降亦會出現(xiàn)在健康的老年人中，此時那些通常一道工作的大腦區(qū)域變得不再默契,，這或許是由于它們彼此間的連接被中斷了,。
由美國哈佛大學的神經(jīng)科學家Jessica Andrews-Hanna和Randy Buckner領導的一個研究小組，利用功能性磁共振成像(fMRI)技術對志愿者——38名20多歲的年輕人以及55名60多歲的老年人——的大腦活動進行了監(jiān)測,。研究人員將目光聚集在大腦區(qū)域的一個“靜態(tài)”網(wǎng)絡——它在大腦空閑,、不用完成任何特定指令時被激活。fMRI掃描揭示了年輕志愿者大腦靜態(tài)網(wǎng)絡中的協(xié)調工作,。例如,，這一網(wǎng)絡中的兩個特殊大腦區(qū)域趨向于在相同的時間被激活，盡管它們一個位于大腦的前端,，而另一個位于大腦的后方,。然而在老年志愿者中，這些大腦區(qū)域的活動很少是協(xié)調進行的,。研究人員對9名老年人的大腦實施了一種正電子發(fā)射斷層掃描（PET）,，這種技術能夠發(fā)現(xiàn)大腦中的淀粉樣蛋白質，后者是阿爾茨海默氏癥的一個標志,。Buckner說,，最終PET掃描的結果呈陰性，表明這種不協(xié)調的靜態(tài)網(wǎng)絡是正常衰老的一部分,，而非疾病的信號,。
另外一項試驗使用了一種名為擴散張量成像的方法，旨在找到那些靜態(tài)網(wǎng)絡活動缺乏協(xié)調的老年人的白質——連接大腦不同區(qū)域的軸突束——惡化的證據(jù),。盡管科學家對靜態(tài)網(wǎng)絡在認知功能中扮演的角色尚不了解,，但是大腦區(qū)域的協(xié)調工作對于人們在記憶測試和其他認知技能方面的表現(xiàn)具有重要影響。那些靜態(tài)網(wǎng)絡中的活動最不協(xié)調的人往往在測試中成績最差,。研究人員在12月6日出版的《神經(jīng)元》（Neuron）雜志上報告了這一研究成果,。
加利福尼亞大學舊金山分校的神經(jīng)科學家Adam Gazzaley說：“我認為這項研究對于認知老化的研究具有重要意義。”他強調,，該發(fā)現(xiàn)加上之前關于因衰老而產(chǎn)生的認知能力下降的線索,，將改變大腦區(qū)域相互作用的方式。Gazzaley指出,，白質惡化可能是一個關鍵的問題,，它中斷了大腦區(qū)域之間的信息流通，從而削弱了它們彼此間協(xié)調工作的能力,。（科學時報）
原始出處:
Neuron, Vol 56, 924-935, 06 December 2007
Article
Disruption of Large-Scale Brain Systems in Advanced Aging
Jessica R. Andrews-Hanna,1,2 Abraham Z. Snyder,3,4 Justin L. Vincent,1,2 Cindy Lustig,5 Denise Head,3,6 Marcus E. Raichle,3,4 and Randy L. Buckner1,2,7,8,
1 Department of Psychology, Center for Brain Science, Harvard University, Cambridge, MA 02138, USA
2 Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA 02129, USA
3 Department of Radiology, Washington University School of Medicine, St. Louis, MO 63110, USA
4 Department of Neurology, Washington University School of Medicine, St. Louis, MO 63110, USA
5 Department of Psychology, University of Michigan, Ann Arbor, MI 48109-1043, USA
6 Department of Psychology, Washington University in St. Louis, St. Louis, MO 63130-4899, USA
7 Department of Radiology, Harvard Medical School, Boston, MA 02155, USA
8 Howard Hughes Medical Institute, Chevy Chase, MD 20815-6789, USA
Corresponding author
Randy L. Buckner
[email protected]
Cognitive decline is commonly observed in advanced aging even in the absence of disease. Here we explore the possibility that normal aging is accompanied by disruptive alterations in the coordination of large-scale brain systems that support high-level cognition. In 93 adults aged 18 to 93, we demonstrate that aging is characterized by marked reductions in normally present functional correlations within two higher-order brain systems. Anterior to posterior components within the default network were most severely disrupted with age. Furthermore, correlation reductions were severe in older adults free from Alzheimer's disease (AD) pathology as determined by amyloid imaging, suggesting that functional disruptions were not the result of AD. Instead, reduced correlations were associated with disruptions in white matter integrity and poor cognitive performance across a range of domains. These results suggest that cognitive decline in normal aging arises from functional disruption in the coordination of large-scale brain systems that support cognition.
