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| 2009/05/12 10:17:06瀏覽550｜回應0｜推薦3 | |
| Dr. Kausik Si 概略式的記憶理論對神經科學有著深遠的意涵。 首先， prions 並非什麼特異的分子。 prions 是生命的必要元素， 擔任著各種各樣有趣的功能。 瑞典科學家甚至發現引起瘋牛症的prion基因和增加長期記憶的關連性。 其他實驗發現當老鼠的下視丘缺乏CPEB， 會引起長期記憶某些特定的缺失。 The rough draft of a theory has profound implications for the neuroscience of memory. First of all, it's proof that prions are not some strange biological apocrypha. In reality, prions are an essential ingredient of life and have all sorts of intriguing functions. Swiss scientists, following up on the research of Si and Kendel, have been discovered a link between the prion gene that causes mad cow disease and increased long-term memory. Essentially, the more likely your neurons are to form misfolded prions, the better your memory is. Other experiments have linked a lack of CPEB in the mouse hippocampus to specific deficits in long-term memory. Though the details remain mostly obscure, there seems to be a deep connection between prions and remembrance. 然而CPEB模型理論也要求我們對記憶的隱喻稍作改變。 我們再也不能想像記憶就是生活的完美反映。 如Proust堅稱， 對過去的回憶不盡然是當時所發生的事實。 Prions CPEB 結構的隨機性正好反映了這個說法。 在某種實驗環境下， CPEB 能呈活性狀態， 譬如一點點的serotonin。 Si 的實驗也顯示， CPEB 能在毫無理由的情況下， 變為活化， 因為CPEB本身蛋白質的折疊性（folding）和化學計量性（stoichiometry）， 其結構能任意轉換。 But the CPEB model also requires that we transform our metaphors for memory. No longer can we imagine memory as a perfect mirror of life. As Proust insisted, the remembrance of things past is not necessarily the remembrance of things as they were. Prions reflect this fact, since they have an element of randomness built into their structure. They don't mind fibbing. While CPEB can switch to an active state under a given set of experimental circumstances (like a few puffs of serotonin), Si's experiments also show that the protein can become active for no real reason, since its transformation is largely dictated by the inscrutable laws of protein folding and stoichiometry. Like memory itself, CPEB delights in its contingency. 神奇的是, CPEB可以完全不依DNA來的指令，改變它的分子結構及形狀，如同記憶 時生時滅。受到serotonin 或dopamine 的刺激，因結構改變而活化。當人思想時，神經細胞會分泌兩種傳導物資，serotonin或dopamine。甚至當神經細胞因故死亡後，CPEB prion還能自由自在地存在於細胞間隙之間， 依循自身的法則而成形。 如Proust所說，“過去被隱藏， 躲在某一個碰觸不到的地方。” This indeterminacy is part of CPEB's design. For a protein, prions are uniquely liberated. They are able to igore everything from the instructions of our DNA to the life cycles of our cells. Though they exist inside us, they are ultimately apart from us, obeying rules of their own making. As Proust said, "The past is hidden....in some material object of which we have no inkling." CPEB 分子似存於時間之外。 這是一個外顯記憶（Explicit Memory）的分子理論。 怎麼說呢？ 因為這個理論包含了我們記憶的隨機性， 因為prions 是不可預測的和不穩定的， 因為記憶除了它自己， 並不尊循甚麼法則。 Proust 知道， 過去永遠不曾過去， 只要我們一息尚存， 我們的記憶始終奇妙地起伏不定。 在記憶銀白的鏡子裡， 我們看到自己。 And though our memory remains inscrutable, the CPEB molecule (if the theory is true) is the synaptic detail that persists outside time. Dr. Si idea is the first hypothesis that begins to explain how sentimental ideas endure. It is why Combray can exist silently below the surface, just behind the curtain of consciousness. It is also why Marcel remembers Combray on page 58, and not page 1. It is a molecular theory of explicit memory that feels true. Why? Because it embraces our essential randomness, because prions are by definition unpredictable and unstable, because memory obeys nothing but itself. This is what Proust knew: the past is never past. As long as we are alive, our memories remain wonderfully volatile. In their mercurial mirror, we see ourselves. |
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| ( 知識學習｜科學百科 ) |
