Is an Early Brain Lesion Prognostically More Advantageous Than a Late Brain Lesion?

腦細胞的可塑性(plasticity)在腦傷後功能的恢復上扮演重要的角色，已有研究顯示未成熟的腦細胞的可塑性比成熟腦細胞的可塑性好，基於此，文獻中常見的主張是早期發生的腦傷比晚期（成人後）發生的腦傷預後好。本文回顧有關腦傷後功能恢復的研究，結論是早期腦傷預後不一定比晚期腦傷好，理由有四：一、雖然在動物實驗或人類研究中，發現年幼罹患腦傷者功能的恢復比年老者快，但前者的恢複並不完全而且只在某些情況下才發生，並且付出相當的代價。二、老鼠研究發現早期腦傷的老鼠，其行為障礙在幼鼠期並不明顯，直到成鼠後行為障礙才出現並且持續存在。三、動物實驗發現並非所有腦細胞的可塑性都伴隨良性的功能恢復。四、一般認為嬰兒腦傷後的恢復潛能比成人大，但愈來愈多的研究指出，在同樣的惡劣條件下（例如：營養或激素的缺乏）較之於成人，嬰兒在腦傷後易產生嚴重的神經上及行為上障礙。基於上述實驗證據，腦傷後功能的恢復受許多因素影響，絕不是單純的時間因素可決定預後的良窩窳。

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The literature on recovery of function contains arguments for and against the advantages for recovery when a cerebral lesion is sustained early in life. This paper evaluated the argument that it is prognostically more advantageous for a lesion incurred earlier than later in life by reviewing studies on recovery of function after brain damage. The empirical evidence showed that it is not necessarily better to have a brain injury earlier in life for the following reasons: First, recovery following an early lesion is not complete and only occurs under certain circumstances. In addition, a substantial price is paid for the recovery to occur under some circumstances. Second, some animal studies found that while behavioral deficits may not be apparent following brain damage during infancy, such deficits may develop and persist later in life. Third, cumulative evidence from research on the relationship between age of onset and brain damage suggests that plasticity in central nervous system are not always beneficial. Fourth, while the infant brain may have more capacity for recovery from neural trauma than the adult brain, the infant brain has been found to be more susceptible to a variety of pathological conditions than the adult brain.

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