人腦可塑性的新發現 並非《超體》所設想

The brain's plasticity and its adaptability to new situations do not function the way researchers previously thought, according to a new study published in the journal Cell. Earlier theories are based on laboratory animals, but now researchers at Karolinska Institutet in Sweden have studied the human brain. The results show that a type of support cell, the oligodendrocyte, which plays an important role in the cell-cell communication in the nervous system, is more sophisticated in humans than in rats and mice -- a fact that may contribute to the superior plasticity of the human brain.

發表在《細胞》雜誌上的一項最新研究表明，大腦的可塑性和對新環境的適應力並非如以前研究者們認爲的那樣。以前的理論都是基於動物實驗研究，如今瑞典卡洛琳斯卡學院的研究者們真正研究了人腦。結果顯示，人腦中的少突膠質細胞（一種支持細胞，在神經系統細胞信息傳輸中起重要作用）比老鼠腦中的要複雜得多，這可能是人腦可塑性更強的原因之一。

The learning process takes place partly by nerve cells creating new connections in the brain. Our nerve cells are therefore crucial for how we store new knowledge. But it is also important that nerve impulses travel at high speed and a special material called myelin plays a vital role. Myelin acts as an insulating layer around nerve fibres, the axons, and large quantities of myelin speed up the nerve impulses and improve function. When we learn something new, myelin production increases in the part of the brain where learning occurs. This interplay, where the brain's development is shaped by the demands that are imposed on it, is what we know today as the brain's plasticity.
學習過程其實正是大腦神經細胞創建新連接的過程。因此，神經細胞對於我們存儲新知識來說是至關重要的。但是，神經衝動高速傳播着，一種叫做髓磷脂的物質也是舉足輕重的。髓磷脂類似於附着在神經纖維和神經突出上的絕緣層，大量的髓磷脂可使得神經衝動加速並改善其功能。當我們學到了新知識時，大腦相應部位的髓磷脂就會增加。腦力的開發受施加其上的壓力的影響。這種相互作用正式我們今天所討論的話題——大腦的可塑性。

Myelin is made by cells known as oligodendrocytes. In the last few years, there has been significant interest in oligodendrocytes and numerous studies have been conducted on mice and rats. These studies have shown that when the nerve cells of laboratory animals need more myelin, the oligodendrocytes are replaced. This is why researchers have assumed that the same also applies in humans. Researchers at Karolinska Institutet and their international collaborators have shown that this is not the case. In humans, oligodendrocyte generation is very low but despite this, myelin production can be modulated and increased if necessary. In other words, the human brain appears to have a preparedness for it, while in mice and rats, increased myelin production relies on the generation of new oligodendrocytes.
髓磷脂是少突膠質細胞的產物。過去幾年，研究者們對它很感興趣，在老鼠身上做了大量實驗。這些實驗表明，當實驗對象的神經細胞需要更多的髓磷脂時，少突膠質細胞就開始了製作過程。基於此研究，研究者假定這現象同樣發生在人腦中。卡洛琳斯卡學院的研究者及其國際合作夥伴發現事實並非如此。人腦中的少突膠質細胞是非常少的，儘管如此，必要時，它還是會生產並調節髓磷脂含量。換句話說，人腦似乎事先早有準備，而老鼠大腦中的髓磷脂的增加依賴少突膠質細胞的更新換代。

In the study in question, researchers have studied the brains of 55 deceased people in the age range from under 1 to 92 years. They were able to establish that at birth most oligodendrocytes are immature. They subsequently mature at a rapid rate until the age of five, when most reach maturity. After this, the turnover rate is very low. Only one in 300 oligodendrocytes are replaced per year, which means that we keep most of these cells our whole lives. This was apparent when the researchers carbon-dated the deceased people's cells. The levels of carbon-14 isotopes rose sharply in the atmosphere after the nuclear weapons tests during the Cold War, and they provided a date mark in the cells. By studying carbon-14 levels in the oligodendrocytes, researchers have been able to determine their age.
在該研究中，科學家們研究了1歲至92歲的55位死者的大腦。他們斷言，新生嬰兒大腦中的少突膠質細胞都是不成熟的，隨後這些細胞迅速生長，在5歲之前大部分成熟了。接下來，它們更新換代的速度很慢。300個少突膠質細胞中每年只有1個更新，這意味着大多數的細胞會伴隨我們終生。研究者們觀察死者腦細胞時發現這是顯而易見的。冷戰期間由於核武器實驗，大氣中的C-14含量迅猛增長。通過研究少突膠質細胞中的-14含量，科學家們可確定死者年齡。

"We were surprised by this discovery. In humans, the existing oligodendrocytes modulate their myelin production, instead of replacing the cells as in mice. It is probably what enables us to adapt and learn faster. Production of myelin is vital in several neurological diseases such as MS. We now have new basic knowledge to build upon," says Jonas Frisén, PhD, Professor of Stem Cell Research at the Department of Cell and Molecular Biology at Karolinska Institutet.
“對於這個發現，我們也很驚訝。少突膠質細胞在人腦中可調節髓磷脂含量，而不像在鼠腦中那樣迅速更新換代。這也許正是我們適應新環境、學習新知識更快的原因。髓磷脂的產生對於治療像MS這樣的神經疾病是至關重要的。現在我們的研究更進了一步。” 卡洛琳斯卡學院細胞和分子生物學系的教授喬納斯說道。