2012年11月1日 讯 /生物谷BIOON/ --近日，来自明尼苏达州大学磁共振研究中心（CMRR）的研究人员发现了一组可以测定时间的神经元，神经元测定时间的过程很难在实验室中进行，相关研究成果刊登于国际杂志PLoS Biology上。
这项研究中，研究者让猴子只依赖内部感官来感知时间的流逝，这项实验的设计可以消除所有可以作为外部“时钟”的线索。研究者训练猴子，让其在没有任何外部提示或者奖励的情况下，眼睛以固定的时间间隔进行移动。研究者发现尽管缺少感觉信息，猴子依然可以准确持续地进行这种行为，猴子这种持续性行为的存在或许因为大脑中特殊区域-侧顶叶（LIP）的活性而致。更有意思的是，研究人员发现，猴子在任务期间大脑LIP的活性与处于外部有提示或者奖励的情况下大脑中的LIP的水平不同。
研究者Geoffrey Ghose博士说，我们的研究发现了LIP的活动可以在计时过程中以持续的比率降低，更重要的是，随着动物神经元的多少，动物的计时情况都会改变。这就好比是这些神经元的活动相当于一个沙漏一样进行工作。
通过开发一种模型来帮助研究者解释定时信号的差别，这项研究揭示了在大脑中并没有中央时钟来进行所有的任务，包括计时。对于不同的活动，大脑所表现出的回路都可以独立地产生一种准确的计时信号。
未来研究中，研究者准备去研究如此精确的定时信号是如何以练习和学习来作为结果的，以及这种信号是否、何时会发生改变。（生物谷Bioon.com）
编译自：How Does the Brain Measure Time?
doi:10.1371/journal.pbio.1001413
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Temporal Production Signals in Parietal Cortex
Blaine A. Schneider, Geoffrey M. Ghose*
We often perform movements and actions on the basis of internal motivations and without any explicit instructions or cues. One common example of such behaviors is our ability to initiate movements solely on the basis of an internally generated sense of the passage of time. In order to isolate the neuronal signals responsible for such timed behaviors, we devised a task that requires nonhuman primates to move their eyes consistently at regular time intervals in the absence of any external stimulus events and without an immediate expectation of reward. Despite the lack of sensory information, we found that animals were remarkably precise and consistent in timed behaviors, with standard deviations on the order of 100 ms. To examine the potential neural basis of this precision, we recorded from single neurons in the lateral intraparietal area (LIP), which has been implicated in the planning and execution of eye movements. In contrast to previous studies that observed a build-up of activity associated with the passage of time, we found that LIP activity decreased at a constant rate between timed movements. Moreover, the magnitude of activity was predictive of the timing of the impending movement. Interestingly, this relationship depended on eye movement direction: activity was negatively correlated with timing when the upcoming saccade was toward the neuron's response field and positively correlated when the upcoming saccade was directed away from the response field. This suggests that LIP activity encodes timed movements in a push-pull manner by signaling for both saccade initiation towards one target and prolonged fixation for the other target. Thus timed movements in this task appear to reflect the competition between local populations of task relevant neurons rather than a global timing signal.
