Not all brains age the same, just as not all bodies age the same.

Intense basic and clinical  research aims at understanding the “normal”  changes in brain structure and function that are associated with aging and why the aged brain is more susceptible to many neurological disorders. While there are some generalizations that can be made about the physical changes the brain undergoes as it ages. Such as decreased levels of certain neurotransmitters or degradation of discrete neuron populations, there is also wide variation in how those physical changes impact cognitive function. In other words, everyone’s brain ages differently.

The good news is that the brain is adaptable at any age. It continues to add and modify its synapses and neural pathways throughout life, in an experience-dependent manner.

That means “use it or lose it”! Brain pathways that are inactive are eventually lost, while an enriching and stimulating life creates a richer network of synapses. This may act as a “neural reserve” against cognitive decline: if the brain is flush with neural pathways then it may be able to use alternate routes to accomplish tasks, like taking a detour around a highway that’s jammed with traffic or under construction.

There have now been a number of cases reported in the scientific literature of older people who had normal or near-normal cognitive function at death, but whose autopsy studies showed extensive brain damage such as what might occur in Alzheimer’s disease. It’s as if their brains had found a way to adapt to a degree of disease pathology that would typically cause severe impairment.

 不是所有大腦的老化過程都一樣,正如我們的身體由發育至衰老,也不是每個人都一樣。大量的基礎及臨床實驗,都在研究人類老化的過程中,大腦會出現的“正常性”結構及功能改變,更希望了解為什麼年老的大腦更易患上各種神經性障礙。現在,可以確定的是,隨著年齡增加,大腦會產生一些生理改變,如神經傳遞物質(Neurotransmitters) 的減少,或神經群(Neuron populations)逐漸分散,但生理改變對大腦認知功能的影響因人而異。換言之,每個人大腦的發展和衰退過程都不一樣。

  好消息是,大腦在任何年齡都有適應性。因應每個人不同的經歷,大腦的突觸及神經元連接可以不斷增加及改變。在用進廢退的原則下,那些不活躍的神經元連接會慢慢流失,而豐富多彩的生活則有助發展和擴大突觸的網絡,大大提升神經元儲藏(Neural reserve),減輕認知能力下降所帶來的影響。這可比喻為當某條高速公路受阻的時候,大腦可運用其四通八達的網絡,用其他通道去完成任務。

  有研究老人大腦的科學文獻,曾經報道過一些案例,這些老人在離世前認知能力大致正常(甚至一切正常),但解剖時卻發現他們的大腦其實已受到有如認知障礙症(Alzheimer’s disease)般嚴重的創傷。在病理學上,這些人理應早就出現嚴重的認知障礙,但誠如上述,他們的大腦卻找到方法適應,如常地生活着。