Ready...go: Amplitude of the FMRI signal encodes expectation of cue arrival time
Cui, Stetson, Montague, Eagleman (2009) Ready...go: Amplitude of the FMRI signal encodes expectation of cue arrival time PLoS Biol (IF: 9.8) 7(8) e1000167
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Abstract
What happens when the brain awaits a signal of uncertain arrival time, as when a sprinter waits for the starting pistol? And what happens just after the starting pistol fires? Using functional magnetic resonance imaging (fMRI), we have discovered a novel correlate of temporal expectations in several brain regions, most prominently in the supplementary motor area (SMA). Contrary to expectations, we found little fMRI activity during the waiting period; however, a large signal appears after the "go" signal, the amplitude of which reflects learned expectations about the distribution of possible waiting times. Specifically, the amplitude of the fMRI signal appears to encode a cumulative conditional probability, also known as the cumulative hazard function. The fMRI signal loses its dependence on waiting time in a "countdown" condition in which the arrival time of the go cue is known in advance, suggesting that the signal encodes temporal probabilities rather than simply elapsed time. The dependence of the signal on temporal expectation is present in "no-go" conditions, demonstrating that the effect is not a consequence of motor output. Finally, the encoding is not dependent on modality, operating in the same manner with auditory or visual signals. This finding extends our understanding of the relationship between temporal expectancy and measurable neural signals.
当大脑等待不确定的到达时间的信号，当一个短跑运动员等待起动手枪时，会发生什么？刚刚开始手枪射击后发生了什么？使用功能磁共振成像（fMRI），我们发现了几个脑区域，最显着的补充运动领域（SMA）时间预期的新型相关。与预期相反，我们在等待期间发现小的fMRI活动;然而，在“走”信号之后出现大的信号，其振幅反映了关于可能的等待时间的分布的学习的期望。具体来说，fMRI信号的幅度似乎编码累积条件概率，也称为累积危险函数。 fMRI信号在“倒计时”条件中丧失其对等待时间的依赖性，其中提前知道走跑线的到达时间，这表明该信号编码时间概率而不是简单地经过时间。信号对时间期望的依赖性存在于“不通过”条件中，表明该效应不是运动输出的结果。最后，编码不依赖于模态，以与听觉或视觉信号相同的方式操作。这个发现扩展了我们对时间预期和可测量的神经信号之间的关系的理解。
Links
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2711330http://www.ncbi.nlm.nih.gov/pubmed/19652698
http://dx.doi.org/10.1371/journal.pbio.1000167
