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A New Type Of Phantom Memory Has Been Found In The Human Brain
A NEW TYPE OF MEMORY – KNOWN AS PRIORITIZED LONG-TERM MEMORY – HAS BEEN DISCOVERED. AGSANDREW/SHUTTERSTOCK
A major spanner has been thrown into the works of the leading theory on , after researchers discovered that the brain is capable of “silently” storing information, creating ghost-like memories that have no neural signature.
It is widely accepted that two types of memory exist. The first of these is known as working memory, and becomes activated when we process new information, keeping it in our minds and focusing on it to ensure we don’t forget it. This is largely controlled by the , where neurons spring into action and fire continuously as we maintain our concentration on whatever it is we are trying to remember.
主流記憶理論迎來重大的革新，研究人員發現大腦能默默地存資訊，製造出幽靈一般的working memory），當我們接收新資訊時會活化，資訊會被我們記住，而且我們會專注在它上面以確保我們不會忘記。這樣的記憶主要被海馬迴（ ）控制，在海馬迴中，當我們專注在記憶東西時，神經會持續活化。，這種記憶沒有經過神經的活動。有兩種記憶的存在被廣泛接受。第一種是工作記憶（
, meanwhile, are stored in the brain’s cortical regions, and are encrypted into specific neural pathways called engrams that become active only when we retrieve these specific memories.
However, in a new study in the journal , researchers report the discovery of a third type of memory, which they are calling “prioritized long-term memory.” The main difference between this and other types of memory is that it doesn’t appear to be actually stored anywhere in the brain, yet can somehow still be recalled when needed.
The team used functional magnetic resonance imaging (fMRI) to monitor the brain activity of participants as they viewed a series of words, faces, and shapes. Thanks to a machine learning algorithm, the researchers were able to identify the particular activity patterns associated with each of these stimuli.
functional magnetic resonance imaging ，fMRI）來觀察實驗參與者在看到一系列文字、臉、形狀時的大腦活動。感謝機器學習演算法，工作人員得以辨別每一種刺激所對應的大腦特定活動模式。同時也儲存在大腦的皮層區域，並且經由稱為「記憶痕跡」的特定的神經路徑加密，它只會在我們回想特定記憶時活化。然而，一分刊載在科學期刊（ ）的研究指出，研究人員發現了第三種類型的記憶，他們稱這種記憶為「優先長期記憶」。這種記憶和其他記憶類型的主要差別在於，這種記憶不是真的被儲存在大腦中，但是卻依然可以被回想。這個研究團隊使用功能性磁共振成像（
They then showed subjects pairs of items, which caused two different activity patterns to emerge in their brains simultaneously. When participants were told to focus on just one of these items and ignore the other, one of these patterns disappeared, suggesting that it had been erased from their working memory.
Scientists had believed that working memory requires neurons to be continuously firing. Andrii Vodolazhskyi/Shutterstock
科學家相信工作記憶需要神經持續的活化。（圖片來源： Andrii Vodolazhskyi/Shutterstock）
Yet in spite of this, subjects were still able to recall this forgotten item when later asked what they had seen, indicating that it still existed somewhere in their memory even though no neurons appeared to be actively remembering it.
“People have always thought neurons would have to keep firing to hold something in memory,” explained study co-author Bradley Postle in a . “But we’re watching people remember things almost perfectly without showing any of the activity that would come with a neuron firing.”
The study authors also found that by magnetically stimulating the brain regions that were associated with these faded memories, they were able to resurrect the activity patterns that had occurred when participants initially focused their attention on these items. This, in turn, caused them to remember these stimuli, even though they were not cued to do so.
While the researchers can’t explain exactly what’s going on here, they suspect that some memories are stored via “actively-silent” mechanisms, whereby information is somehow held in the synapses between neurons, even when these neurons are not active.