斑马鱼能够令人惊讶地准确掌握不同的节奏。（图片提供:German Sumbre）
就像一名蓝调音乐家不停地用脚和着乐曲打拍子一样，斑马鱼竟然能学会随着闪光灯的节奏拍打它们的尾巴，并且在灯光熄灭后依然可以记住这些节奏。这一令人惊讶的发现为研究动物如何测量时间提供了线索。研究人员在最近的英国《自然》（Nature）杂志网络版上报告了这一研究成果。
人类和其他动物通过一个内在的生物钟——即生理节奏的节律，负责调节24小时的睡眠、进食和其他活动——来辨析时间。但如果是一些更小的时间增量呢？例如，动物必须能够感知一头正在接近的食肉动物的速度到底有多快。美国加利福尼亚大学伯克利分校的神经生物学家Mu-ming Poo表示：“控制分秒生物钟的机制依然是个未解之谜。”
于是，Poo的研究小组开始研究大脑中的神经细胞如何在更短的尺度上感知时间。研究人员将年幼的斑马鱼——一种常见的实验室模式动物——暴露在不同长短和频率的闪光下。他们随后观测了闪光刺激前后顶盖——负责处理视觉信息的大脑区域——中的神经活动。研究人员注意到，当闪光停止后，顶盖中的神经活动的特殊模式还将持续20秒钟，这意味着斑马鱼记住了这些闪光。事实上，当光线消失后，斑马鱼能够以令人惊讶的精准节奏继续拍打它们的尾巴，就像是一部节拍器。Poo表示：“在闪光结束后，斑马鱼能够近乎完美地复制节奏——尽管是在很短的时间段内。”
美国加利福尼亚大学洛杉矶分校的神经学家Dean Buonomano认为，这项研究提供了后天行为与神经活动之间的一个“极佳的”例证。但是从事大脑辨析时间研究的Buonomano指出， 由于在这项研究中，斑马鱼对人造刺激的响应仅仅类似于一部节拍器，因此尚不清楚它们体内的生物钟究竟是如何测量很短的时间间隔的。（生物谷Bioon.com）
生物谷推荐原始出处：
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 Neuroscience Institute, University of California, Berkeley, California 94720, USA
2 Department of Physiology, University of California, San Francisco, California 94158, USA
3 Present address: Laboratoire de Neurobiologie, UMR 8544, école Normale Supérieure, 46 rue d'Ulm, 75005 Paris, France.
The ability to process temporal information is fundamental to sensory perception, cognitive processing and motor behaviour of all living organisms, from amoebae to humans1, 2, 3, 4. Neural circuit mechanisms based on neuronal and synaptic properties have been shown to process temporal information over the range of tens of microseconds to hundreds of milliseconds5, 6, 7. How neural circuits process temporal information in the range of seconds to minutes is much less understood. Studies of working memory in monkeys and rats have shown that neurons in the prefrontal cortex8, 9, 10, the parietal cortex9, 11 and the thalamus12 exhibit ramping activities that linearly correlate with the lapse of time until the end of a specific time interval of several seconds that the animal is trained to memorize. Many organisms can also memorize the time interval of rhythmic sensory stimuli in the timescale of seconds and can coordinate motor behaviour accordingly, for example, by keeping the rhythm after exposure to the beat of music. Here we report a form of rhythmic activity among specific neuronal ensembles in the zebrafish optic tectum, which retains the memory of the time interval (in the order of seconds) of repetitive sensory stimuli for a duration of up to 20 s. After repetitive visual conditioning stimulation (CS) of zebrafish larvae, we observed rhythmic post-CS activities among specific tectal neuronal ensembles, with a regular interval that closely matched the CS. Visuomotor behaviour of the zebrafish larvae also showed regular post-CS repetitions at the entrained time interval that correlated with rhythmic neuronal ensemble activities in the tectum. Thus, rhythmic activities among specific neuronal ensembles may act as an adjustable 'metronome' for time intervals in the order of seconds, and serve as a mechanism for the short-term perceptual memory of rhythmic sensory experience.
