研究表明，海馬細(xì)胞活動(dòng)的內(nèi)在觸發(fā)與記憶的喚起有關(guān),。
人體海馬神經(jīng)元中的一些細(xì)胞能夠增加它們響應(yīng)特定目標(biāo),、場(chǎng)景,、范疇或人的活性,，而在小鼠中,，一套類似的神經(jīng)細(xì)胞在特定的環(huán)境中也會(huì)被激活。如今,，發(fā)表在《科學(xué)》雜志上的兩項(xiàng)研究表明,，這些細(xì)胞的活性同時(shí)也能夠在內(nèi)部產(chǎn)生,，這可能與記憶的喚起有關(guān)。
美國(guó)新澤西州立大學(xué)的Gyorgy Buzsáki和同事訓(xùn)練小鼠穿過(guò)具有兩個(gè)通道的迷宮,，在這里小鼠被要求不是向左走就是向右走,，以便獲得獎(jiǎng)勵(lì),。在每次訓(xùn)練中，小鼠都能夠記得上次訓(xùn)練所走的路,，并選擇相反的方向,。在試驗(yàn)當(dāng)中，這些小鼠有10到20秒的時(shí)間在一個(gè)轉(zhuǎn)動(dòng)的輪子中奔跑,。與預(yù)期的一樣,，來(lái)自海馬神經(jīng)元的記錄揭示了椎體細(xì)胞——即所謂的“位置細(xì)胞”——在小鼠在迷宮中行動(dòng)時(shí)被短暫地激活了。然而,，大約一半被記錄的椎體細(xì)胞在小鼠于輪子中跑動(dòng)時(shí)也表現(xiàn)出了類似的短暫活性：不同的神經(jīng)細(xì)胞組合在特定的時(shí)間被激活,，所以“情節(jié)神經(jīng)細(xì)胞”的每種組合都有一個(gè)特定的“情節(jié)領(lǐng)域”。因此,，在迷宮導(dǎo)航期間觀察到的海馬神經(jīng)元的特定活性也發(fā)生在動(dòng)物無(wú)需導(dǎo)航的時(shí)候,。重要的是，這種情節(jié)活性與記憶和工作的編程特征相關(guān),，這是因?yàn)樗](méi)有出現(xiàn)在轉(zhuǎn)輪情節(jié)并未成為記憶的一部分的對(duì)照組中,。
此外，作者指出,，在輪子轉(zhuǎn)動(dòng)期間的細(xì)胞組合活性預(yù)示了動(dòng)物在接下來(lái)的迷宮導(dǎo)航情節(jié)中將要作出的（向左或向右的）選擇,，即便對(duì)于那些在試驗(yàn)中錯(cuò)誤的選擇也是如此。這些發(fā)現(xiàn)表明,，除了被環(huán)境線索觸發(fā)外,，連續(xù)的神經(jīng)細(xì)胞組合行為能夠在內(nèi)部被觸發(fā)并持續(xù)。據(jù)此推測(cè),，在輪子轉(zhuǎn)動(dòng)期間,，小鼠回憶起它們之前的迷宮路徑，為的是計(jì)劃下一步所選擇的方向,。
在一項(xiàng)相關(guān)的研究中,，美國(guó)加利福尼亞大學(xué)洛杉磯分校的Itzhak Fried和同事提供了直接證據(jù),，表明海馬細(xì)胞活動(dòng)的內(nèi)在觸發(fā)與記憶的喚起有關(guān),。他們對(duì)癲癇癥患者進(jìn)行了研究，這些人的大腦中被植入了電極,。這些病人觀看了有關(guān)名人,、電視人物,、事件或動(dòng)物的一組聲像短片,。這些短片被放映了幾遍，然后這些病人被要求口頭回憶他們剛剛看過(guò)的片段,。作為對(duì)一個(gè)或多個(gè)片段的響應(yīng),，大腦內(nèi)側(cè)顳葉中超過(guò)一半被記錄的神經(jīng)細(xì)胞都表現(xiàn)出了短暫的活性提升,。在這些細(xì)胞的激活速度以一種持續(xù)不斷的形式上升期間,，這些神經(jīng)細(xì)胞中的一部分看起來(lái)具有一個(gè)“首選的”片段，至關(guān)重要的是,，在海馬和內(nèi)嗅皮質(zhì)中,，選擇性神經(jīng)細(xì)胞在受試者口頭回憶觀看的短片前平均3秒鐘也增加了它們的激活速度，但是其他神經(jīng)細(xì)胞則在回憶“非首選的”短片時(shí)保持沉默,。
這兩項(xiàng)研究表明,，海馬神經(jīng)元的選擇活性不但發(fā)生在對(duì)特定環(huán)境線索的響應(yīng)中，同時(shí)也能夠在內(nèi)部產(chǎn)生,，這可能是回憶一段記憶引發(fā)了神經(jīng)細(xì)胞更早前的活動(dòng),。單個(gè)海馬神經(jīng)元內(nèi)部產(chǎn)生的再活化可能表現(xiàn)為與神經(jīng)系統(tǒng)有關(guān)的記憶喚起,，而未來(lái)的研究將必須建立神經(jīng)活動(dòng)所表現(xiàn)的環(huán)境線索（或聲像片段）的特征,。（生物谷Bioon.com）
生物谷推薦原始出處：
Science 5 September 2008: DOI: 10.1126/science.1159775
Internally Generated Cell Assembly Sequences in the Rat Hippocampus
Eva Pastalkova, Vladimir Itskov,* Asohan Amarasingham, Gy?rgy Buzsáki
A long-standing conjecture in neuroscience is that aspects of cognition depend on the brain's ability to self-generate sequential neuronal activity. We found that reliably and continually changing cell assemblies in the rat hippocampus appeared not only during spatial navigation but also in the absence of changing environmental or body-derived inputs. During the delay period of a memory task, each moment in time was characterized by the activity of a particular assembly of neurons. Identical initial conditions triggered a similar assembly sequence, whereas different conditions gave rise to different sequences, thereby predicting behavioral choices, including errors. Such sequences were not formed in control (nonmemory) tasks. We hypothesize that neuronal representations, evolved for encoding distance in spatial navigation, also support episodic recall and the planning of action sequences.
Center for Molecular and Behavioral Neuroscience, Rutgers, The State University of New Jersey, 197 University Avenue, Newark, NJ 07102, USA.
Science 3 October 2008: DOI: 10.1126/science.1164685
Internally Generated Reactivation of Single Neurons in Human Hippocampus During Free Recall
Hagar Gelbard-Sagiv,1 Roy Mukamel,2 Michal Harel,1 Rafael Malach,1 Itzhak Fried2,3*
The emergence of memory, a trace of things past, into human consciousness is one of the greatest mysteries of the human mind. Whereas the neuronal basis of recognition memory can be probed experimentally in human and nonhuman primates, the study of free recall requires that the mind declare the occurrence of a recalled memory (an event intrinsic to the organism and invisible to an observer). Here, we report the activity of single neurons in the human hippocampus and surrounding areas when subjects first view cinematic episodes consisting of audiovisual sequences and again later when they freely recall these episodes. A subset of these neurons exhibited selective firing, which often persisted throughout and following specific episodes for as long as 12 seconds. Verbal reports of memories of these specific episodes at the time of free recall were preceded by selective reactivation of the same hippocampal and entorhinal cortex neurons. We suggest that this reactivation is an internally generated neuronal correlate for the subjective experience of spontaneous emergence of human recollection.
1 Department of Neurobiology, Weizmann Institute of Science, Rehovot, 76100, Israel.
2 Department of Neurosurgery, David Geffen School of Medicine, and Semel Institute for Neuroscience and Human Behavior, University of California Los Angeles, Los Angeles, CA 90095, USA.
3 Functional Neurosurgery Unit, Tel Aviv Medical Center and Sackler School of Medicine, Tel Aviv University, Tel Aviv, 64239, Israel.
