Toni I, Krams M, Turner R, Passingham R E
Wellcome Department of Cognitive Neurology, Institute of Neurology, London, United Kingdom.
Neuroimage. 1998 Jul;8(1):50-61. doi: 10.1006/nimg.1998.0349.
There is a discrepancy between the results of imaging studies in which subjects learn motor sequences. Some experiments have shown decreases in the activation of some areas as learning increased, whereas others have reported learning-related increases as learning progressed. We have exploited fMRI to measure changes in blood oxygen leve-dependent (BOLD) signal throughout the course of learning. T2*-weighted echo-planar images were acquired over the whole brain for 40 min while the subjects learned a sequence eight moves long by trial and error. The movements were visually paced every 3.2 s and visual feedback was provided to the subjects. A baseline period followed each activation period. The effect due to the experimental conditions was modeled using a square-wave function, time locked to their occurrence. Changes over time in the difference between activation and baseline signal were modeled using a set of polynomial basis functions. This allowed us to take into account linear as well as nonlinear changes over time. Low-frequency changes over time common to both activation and baseline conditions (and thus not learning related) were modeled and removed. Linear and nonlinear changes of BOLD signal over time were found in prefrontal, premotor, and parietal cortex and in neostriatal and cerebellar areas. Single-unit recordings in nonhuman primates during the learning of motor tasks have clearly shown increased activity early in learning, followed by a decrease as learning progressed. Both phenomena can be observed at the population level in the present study.
在关于受试者学习运动序列的成像研究结果之间存在差异。一些实验表明，随着学习的增加，某些区域的激活会减少，而另一些实验则报告随着学习的进展，与学习相关的激活会增加。我们利用功能磁共振成像（fMRI）来测量在学习过程中血氧水平依赖（BOLD）信号的变化。在受试者通过试错学习一个八步长的序列时，对全脑采集了40分钟的T2*加权回波平面图像。动作每3.2秒进行一次视觉同步，并向受试者提供视觉反馈。每个激活期之后是一个基线期。使用与实验条件出现时间锁定的方波函数对实验条件产生的效应进行建模。使用一组多项式基函数对激活信号与基线信号之差随时间的变化进行建模。这使我们能够考虑到随时间的线性以及非线性变化。对激活和基线条件共有的随时间的低频变化（因此与学习无关）进行建模并去除。在前额叶、运动前区、顶叶皮层以及新纹状体和小脑区域发现了BOLD信号随时间的线性和非线性变化。在非人类灵长类动物学习运动任务期间的单细胞记录清楚地表明，在学习早期活动增加，随后随着学习的进展而减少。在本研究的群体水平上可以观察到这两种现象。
