About 50 years ago, neuroscientists discovered a type of cell in the brain's hippocampus that is associated with storing memories of specific locations. These cells are not only essential for spatial memory, but also play an important role in storing episodic memories. Although the scientific community has a deep understanding of the mechanism by which these place cells encode spatial memories, how they participate in the encoding of episodic memories remains a mystery.

大約 50 年前，神經(jīng)科學家在大腦海馬體中發(fā)現(xiàn)了一種與存儲特定位置記憶相關(guān)的細胞。 這些細胞不僅對空間記憶至關(guān)重要，在存儲情節(jié)記憶方面同樣發(fā)揮著重要作用。 盡管科學界已經(jīng)深入了解這些位置細胞編碼空間記憶的機制，但它們?nèi)绾螀⑴c情節(jié)記憶的編碼仍然是一個未解之謎。

A new model developed by MIT researchers provides new insights into this question, showing that place cells can work with grid cells in the entorhinal cortex to act as a scaffold to organize memories into an interconnected sequence without spatial information.

近期，MIT 研究人員開發(fā)的一種新模型為這一問題提供了新的見解。 該模型表明，位置細胞可以在沒有空間信息的情況下與內(nèi)嗅皮層的網(wǎng)格細胞協(xié)作，充當一種支架，將記憶組織成一個相互關(guān)聯(lián)的序列。

"This model provides a preliminary understanding of the role of the entorhinal cortex and hippocampus in the episodic memory circuit and provides a foundation for understanding the nature of episodic memory," says Ila Fiete, a professor of brain and cognitive sciences at MIT, a member of the McGovern Institute for Brain Research, and senior author of the new study.

“這個模型初步揭示了內(nèi)嗅皮層與海馬體在情節(jié)記憶回路中的作用，為理解情節(jié)記憶的本質(zhì)提供了基礎(chǔ)?！?MIT 大腦與認知科學系教授、麥戈文腦研究所成員、這項新研究的資深作者 Ila Fiete 表示。

This model successfully reproduces several key features of the biological memory system, including its huge storage capacity, the gradual decay of old memories, and people's ability to store large amounts of information through the "memory palace" technique.

這個模型成功再現(xiàn)了生物記憶系統(tǒng)的多個關(guān)鍵特征，包括巨大的存儲容量、舊記憶的逐步衰退，以及人們通過“記憶宮殿”技術(shù)存儲大量信息的能力。
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The study was led by MIT research scientists Sarthak Chandra and Sugandha Sharma, and the results were recently published in Nature. Rishidev Chaudhuri, an assistant professor at the University of California, Davis, also participated in the study.

這項研究由MIT研究科學家Sarthak Chandra和Sugandha Sharma共同主導(dǎo)完成，研究成果已于近期發(fā)表在自然雜志上。 加州大學戴維斯分校助理教授 Rishidev Chaudhuri 也參與了這項研究。

Memory Index

記憶的索引

To encode spatial memories, place cells in the hippocampus work closely with grid cells, a special type of neuron that fires in multiple different locations and is arranged in a regular pattern of repeating triangular geometries. Together, groups of grid cells form a triangular network that represents physical space.

為了編碼空間記憶，海馬體中的位置細胞與網(wǎng)格細胞密切合作。 網(wǎng)格細胞是一類特殊的神經(jīng)元，它們會在多個不同的位置被激活，并按照重復(fù)的三角形幾何圖案規(guī)律地排列在一起。 網(wǎng)格細胞群體共同形成了一個三角形網(wǎng)絡(luò)，用于表示物理空間。

"The same hippocampus and entorhinal circuits are used for both spatial memory and general episodic memory," Fiete explained. "So a further question we could explore is, what is the connection between spatial memory and episodic memory that allows them to share the same circuit?"

“同樣的海馬體和內(nèi)嗅回路既用于空間記憶，也用于一般的情節(jié)記憶?！?Fiete 解釋道，“因此我們可以進一步探討的問題是，空間記憶和情節(jié)記憶之間存在什么樣的聯(lián)系，使它們能夠共享同一個回路？”

There are two main hypotheses for this overlap. The first hypothesis is that the main function of this circuit is to store spatial memory (for example, remembering where food is or where predators are, because such memories are essential for survival). In this view, the encoding of episodic memory is considered a byproduct of spatial memory.

針對這一功能重疊，科學界提出了兩種主要假設(shè)。 第一種假設(shè)認為，這一回路的主要功能是存儲空間記憶（例如記住食物在哪里或捕食者出現(xiàn)的地方，因為這類記憶對于生存至關(guān)重要）。 在這種觀點下，情節(jié)記憶的編碼被認為是空間記憶的一種副產(chǎn)品。

The second hypothesis, in contrast, proposes that this circuit is primarily used to store episodic memories, but can also encode spatial memories, as place is often an important component of episodic memory.

第二種假設(shè)則相反，認為這一回路主要用于存儲情節(jié)記憶，同時也能編碼空間記憶，因為地點通常是情節(jié)記憶中的一個重要組成部分。

In this study, Fiete and her team proposed a third possibility: that the unique tiled structure of grid cells and their interaction with the hippocampus are equally important for both types of memory, episodic and spatial. To develop this new model, they drew on computational models developed in Fiete's lab over the past decade that simulate how grid cells efficiently encode spatial information.

在這項研究中，F(xiàn)iete和她的團隊提出了第三種可能性：網(wǎng)格細胞的獨特平鋪結(jié)構(gòu)及其與海馬體的相互作用，對情節(jié)記憶和空間記憶這兩種記憶類型同樣重要。 為了開發(fā)這一新模型，他們借鑒了 Fiete 實驗室過去十年中開發(fā)的計算模型，這些模型模擬了網(wǎng)格細胞如何高效編碼空間信息。

"We've reached a point where I think we have a good understanding of the mechanisms of the grid cell circuit, so now it's time to explore the interactions between grid cells and larger circuits that include the hippocampus," Fiete said.

“我們已經(jīng)到了這樣一個階段，我認為我們對網(wǎng)格細胞回路的機制有了一定程度的理解，因此現(xiàn)在是時候探索網(wǎng)格細胞與包括海馬體在內(nèi)的更大回路之間的相互作用了?！?Fiete 說道。

In this new model, the interaction between grid cells and hippocampal cells can serve as a scaffold for storing spatial or episodic memories. Each activation pattern in the grid defines a "well," which is arranged at regular intervals. It is important to note that these wells do not directly store the content of a specific memory, but rather act as a "pointer" to a specific memory. The specific memory content is stored in the synapses between the hippocampus and the sensory cortex.

在這個新模型中，網(wǎng)格細胞與海馬細胞的相互作用可以作為存儲空間記憶或情節(jié)記憶的支架。 網(wǎng)格中的每種激活模式定義了一個“井”，這些井按照規(guī)則的間隔排列。 需要注意的是，這些井并不直接存儲特定記憶的內(nèi)容，而是充當指向特定記憶的“指針”。 具體的記憶內(nèi)容則被存儲在海馬體與感覺皮層之間的突觸中。

When the memory is later triggered by fragmented fragments, the interaction between grid cells and hippocampal cells guides the circuit state to the nearest "well". The bottom state of these wells is connected to the corresponding part of the sensory cortex, which fills in the details of the memory. Because the sensory cortex is much larger than the hippocampus, it can store a large amount of memory information, thus compensating for the limited capacity of the hippocampus.

當記憶稍后被零散的片段觸發(fā)時，網(wǎng)格細胞和海馬細胞之間的相互作用會將回路狀態(tài)引導(dǎo)至最近的“井”。 這些井的底部狀態(tài)與感覺皮層的相應(yīng)部分相連，補充了記憶的細節(jié)。 由于感覺皮層的規(guī)模遠大于海馬體，它能夠存儲大量的記憶信息，從而彌補海馬體容量的限制。

"Conceptually, we can think of the hippocampus as a pointer network," Fiete explained. "It acts like an index, taking in partial inputs to complete a pattern and then pointing those inputs to the sensory cortex, where these memories are initially experienced and encoded. This scaffold does not contain the specific content of the memory; it only contains an index to an abstract scaffold state."

“從概念上看，我們可以將海馬體視為一個指針網(wǎng)絡(luò)。” Fiete 解釋道，“它的作用類似于一個索引，通過接收部分輸入完成模式補全，然后將這些輸入指向感覺皮層（即這些記憶最初被體驗和編碼的地方），這種支架并不包含記憶的具體內(nèi)容，它只包含指向抽象支架狀態(tài)的索引。”

This structure enables events that occur in sequence to be lixed together: each "well" in the grid cell-hippocampal network effectively stores the information needed to activate the next "well", allowing memories to be recalled in the correct order.

這樣的結(jié)構(gòu)使按順序發(fā)生的事件能夠被連結(jié)在一起：網(wǎng)格細胞-海馬網(wǎng)絡(luò)中的每個“井”有效地存儲了激活下一個“井”所需的信息，從而使得記憶能夠以正確的順序被回憶。

Modeling Memory Cliffs and Memory Palaces

建模記憶斷崖與記憶宮殿
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The researchers' new model reproduced several memory-related phenomena more accurately than existing models based on Hopfield networks, a type of neural network that can store and recall patterns and provided important early insights into how memories form, particularly how information is stored by strengthening connections between neurons.

研究人員的新模型在再現(xiàn)多個與記憶相關(guān)的現(xiàn)象方面比基于 Hopfield 網(wǎng)絡(luò)的現(xiàn)有模型更為準確。 Hopfield 網(wǎng)絡(luò)是一種能夠存儲和回憶模式的神經(jīng)網(wǎng)絡(luò)，為記憶的形成提供了早期的重要見解，尤其是關(guān)于如何通過增強神經(jīng)元之間的連接來存儲信息。

However, the Hopfield network does not perfectly simulate how biological memory actually works. In this model, each memory can be recalled in great detail until the limit of storage capacity is reached. Once this limit is reached, not only is the model unable to form new memories, but even attempting to add new memories results in the complete loss of all previous memories.

然而，Hopfield 網(wǎng)絡(luò)并不能完美模擬生物記憶的實際工作方式。 在這種模型中，每個記憶都可以被細致入微地回憶，直到達到存儲容量的極限。 一旦達到這個極限，模型不僅無法形成新的記憶，甚至試圖添加新記憶會導(dǎo)致所有先前記憶的完全丟失。

This "memory cliff" phenomenon does not match the actual mechanism of the biological brain. In contrast, the memory system of the biological brain is more flexible: the details of old memories will gradually blur over time, but they will not disappear completely, and new memories can be continuously stored.

這種記憶斷崖的現(xiàn)象與生物大腦的真實機制并不相符。 與之相比，生物大腦的記憶系統(tǒng)更加靈活：舊記憶的細節(jié)會隨著時間逐漸模糊，但不會完全消失，同時可以不斷存儲新記憶。
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The new MIT model successfully captures key insights accumulated over decades of research on grid cells and hippocampal cell recordings, primarily from studies of rodents exploring and foraging in a variety of environments. More importantly, the model also helps reveal the mechanisms behind a well-known memory strategy known as the "memory palace."

MIT 的新模型成功捕捉了數(shù)十年來通過研究網(wǎng)格細胞和海馬細胞記錄所積累的關(guān)鍵發(fā)現(xiàn)。 這些記錄主要來自嚙齒動物在各種環(huán)境中探索和覓食行為的研究。 更重要的是，該模型還幫助揭示了一種廣為人知的記憶策略（即“記憶宮殿”）背后的機制。

In memory competitions, one of the tasks for contestants is to remember one or more shuffled decks of playing cards. They typically accomplish this by assigning each card to a specific location in a "memory palace." This is often a mental representation of a childhood home or other familiar place, and when the cards need to be recalled, they mentally walk through the palace, seeing the cards in turn at each location along the way. At first glance, associating cards with locations may seem to add an extra burden to the memory, but in fact, this method makes memories more solid and reliable.

在記憶力比賽中，參賽者的一項任務(wù)是記住一副或多副打亂順序的撲克牌。 他們通常通過將每張牌分配到“記憶宮殿”的特定位置來完成這一任務(wù)。 記憶宮殿通常是對童年家園或其他熟悉場所的腦海再現(xiàn)，當需要回憶這些牌時，他們會在腦海中漫步在這個宮殿中，沿途在每個位置依次看到這些牌。 乍一看，將牌與位置相關(guān)聯(lián)似乎增加了額外的記憶負擔，但實際上，這種方法讓記憶變得更加牢固和可靠。

The MIT team's computational model was able to perform tasks similar to the "Memory Palace" very well, suggesting that this memory strategy actually exploits the natural mechanism of the memory circuit. By associating input with scaffolds in the hippocampus and combining long-term memories stored in the sensory cortex as new scaffolds, this approach significantly expands the capacity of the memory system, allowing humans to store and recall more sequence information than usual.

MIT 團隊的計算模型能夠出色地完成類似“記憶宮殿”的任務(wù)，這表明這種記憶策略實際上是利用了記憶回路的自然機制。 通過將輸入與海馬體中的支架關(guān)聯(lián)起來，并結(jié)合長期存儲在感覺皮層中的記憶作為新的支架，這種方法顯著擴展了記憶系統(tǒng)的容量，使得人類能夠存儲和回憶比平時更多的序列信息。

Next, the researchers plan to further explore several important issues based on this model, such as how episodic memory is converted into semantic memory in the cortex, that is, factual memory that is independent of the specific context when it is acquired, such as "Paris is the capital of France"; how events are defined and organized; and how to integrate brain-like memory models into modern machine learning systems to enhance the memory and learning capabilities of artificial intelligence.

接下來，研究人員計劃基于這一模型進一步探索幾個重要問題，比如情節(jié)記憶如何轉(zhuǎn)化為皮層中的語義記憶，即與獲取時的具體情境無關(guān)的事實性記憶，例如巴黎是法國的首都; 事件如何被定義和組織; 以及如何將類腦記憶模型整合到現(xiàn)代機器學習系統(tǒng)中，從而提升人工智能的記憶和學習能力。