來源:科學時報
斑馬魚能夠令人驚訝地準確掌握不同的節奏。就像一名藍調音樂家不停地用腳和著樂曲打拍子一樣，斑馬魚竟然能學會隨著閃光燈的節奏拍打它們的尾巴，并且在燈光熄滅后依然可以記住這些節奏。這一令人驚訝的發現為研究動物如何測量時間提供了線索。研究人員在*近的英國《自然》（Nature）雜志網絡版上報告了這一研究成果。
人類和其他動物通過一個內在的生物鐘——即生理節奏的節律，負責調節24小時的睡眠、進食和其他活動——來辨析時間。但如果是一些更小的時間增量呢？例如，動物必須能夠感知一頭正在接近的食肉動物的速度到底有多快。美國加利福尼亞大學伯克利分校的神經生物學家Mu-ming Poo表示：“控制分秒生物鐘的機制依然是個未解之謎。”
于是，Poo的研究小組開始研究大腦中的神經細胞如何在更短的尺度上感知時間。研究人員將年幼的斑馬魚——一種常見的實驗室模式動物——暴露在不同長短和頻率的閃光下。他們隨后觀測了閃光刺激前后頂蓋——負責處理視覺信息的大腦區域——中的神經活動。研究人員注意到，當閃光停止后，頂蓋中的神經活動的特殊模式還將持續20秒鐘，這意味著斑馬魚記住了這些閃光。事實上，當光線消失后，斑馬魚能夠以令人驚訝的精準節奏繼續拍打它們的尾巴，就像是一部節拍器。Poo表示：“在閃光結束后，斑馬魚能夠近乎**地復制節奏——盡管是在很短的時間段內。”
美國加利福尼亞大學洛杉磯分校的神經學家Dean Buonomano認為，這項研究提供了后天行為與神經活動之間的一個“**的”例證。但是從事大腦辨析時間研究的Buonomano指出， 由于在這項研究中，斑馬魚對人造刺激的響應僅僅類似于一部節拍器，因此尚不清楚它們體內的生物鐘究竟是如何測量很短的時間間隔的。（創賽新聞中心Canspec.com）
原始出處：
Nature，doi:10.1038/nature07351，Germán Sumbre，Mu-ming Poo
Entrained rhythmic activities of neuronal ensembles as perceptual memory of time interval
Germán Sumbre1,3, Akira Muto2,Herwig Baier2 & Mu-ming Poo1
1 Division of Neurobiology,Department of Molecular and Cell Biology, Helen Wills NeuroscienceInstitute, University of California, Berkeley, California 94720,USA
2 Department of Physiology, University of California, SanFrancisco, California 94158, USA
3 Present address: Laboratoire de Neurobiologie, UMR 8544, écoleNormale Supérieure, 46 rue d'Ulm, 75005 Paris,France.
Theability to process temporal information is fundamental to sensoryperception, cognitive processing and motor behaviour of all livingorganisms, from amoebae tohumans1, 2, 3, 4.Neural circuit mechanisms based on neuronal and synaptic propertieshave been shown to process temporal information over the range oftens of microseconds to hundreds ofmilliseconds5, 6, 7.How neural circuits process temporal information in the range ofseconds to minutes is much less understood. Studies of workingmemory in monkeys and rats have shown that neurons in theprefrontal cortex8, 9, 10,the parietal cortex9, 11 andthe thalamus12 exhibitramping activities that linearly correlate with the lapse of timeuntil the end of a specific time interval of several seconds thatthe animal is trained to memorize. Many organisms can also memorizethe time interval of rhythmic sensory stimuli in the timescale ofseconds and can coordinate motor behaviour accordingly, forexample, by keeping the rhythm after exposure to the beat of music.Here we report a form of rhythmic activity among specific neuronalensembles in the zebrafish optic tectum, which retains the memoryof the time interval (in the order of seconds) of repetitivesensory stimuli for a duration of upto 20 s. After repetitive visual conditioning stimulation (CS) ofzebrafish larvae, we observed rhythmic post-CS activities amongspecific tectal neuronal ensembles, with a regular interval thatclosely matched the CS. Visuomotor behaviour of the zebrafishlarvae also showed regular post-CS repetitions at the entrainedtime interval that correlated with rhythmic neuronal ensembleactivities in the tectum. Thus, rhythmic activities among specificneuronal ensembles may act as an adjustable 'metronome' for timeintervals in the order of seconds, and serve as a mechanism for theshort-term perceptual memory of rhythmic sensoryexperience.
