Imamizu Hiroshi, Higuchi Satomi, Toda Akihiro, Kawato Mitsuo
ATR Computational Neuroscience Laboratories, Kyoto, Japan.
Cortex. 2007 Apr;43(3):338-49. doi: 10.1016/s0010-9452(08)70459-3.
Internal models are neural mechanisms that can mimic the input-output properties of controlled objects. Our studies have shown that: 1) an internal model for a novel tool is acquired in the cerebellum (Imamizu et al., 2000); 2) internal models are modularly organized in the cerebellum (Imamizu et al., 2003); 3) their outputs are sent to the premotor regions after learning (Tamada et al., 1999); and 4) the prefrontal and parietal regions contribute to the blending of the outputs (Imamizu et al., 2004). Here, we investigated changes in global neural networks resulting from the acquisition of a new internal model. Human subjects manipulated three types of rotating joystick whose cursor appeared at a position rotated 60 degrees, 110 degrees, or 160 degrees around the screen's center. In a pre-test after long-term training (5 days) for the 60 degrees and 160 degrees joysticks, brain activation was scanned during manipulation of the three joysticks. The subjects were then trained for the 110 degrees for only 25 min. In a post-test, activation was scanned using the same method as the pre-test. Comparisons of the post-test to the pre-test revealed that the volume of activation decreased in most of the regions where activation for the three rotations was observed. However, there was an increase in volume at a marginally significant level (p < .08) only in the inferior-lateral cerebellum and only for the 110 degrees joystick. In the cerebral cortex, activation related to 110 degrees decreased in the prefrontal and parietal regions but increased in the premotor and supplementary motor area (SMA) regions. These results can be explained by a model in which outputs of the 60 degrees and 160 degrees internal models are blended by prefrontal and parietal regions to cope with the novel 110 degrees joystick before the 25-minute training; after the acquisition within the cerebellum of an internal model for the 110 degrees, output is directly sent to the premotor and SMA regions, and activation in these regions increases.
内部模型是能够模拟受控对象输入输出特性的神经机制。我们的研究表明：1）小脑会获取新工具的内部模型（今泉等，2000年）；2）内部模型在小脑中呈模块化组织（今泉等，2003年）；3）学习后其输出会发送到运动前区（玉田等，1999年）；4）前额叶和顶叶区域有助于输出的融合（今泉等，2004年）。在此，我们研究了因获取新内部模型而导致的全局神经网络变化。人类受试者操控三种类型的旋转操纵杆，其光标出现在围绕屏幕中心旋转60度、110度或160度的位置。在对60度和160度操纵杆进行长期训练（5天）后的预测试中，在操纵这三种操纵杆期间对大脑激活情况进行扫描。然后受试者仅对110度操纵杆进行25分钟的训练。在测试后，使用与预测试相同的方法对激活情况进行扫描。测试后与测试前的比较显示，在观察到三种旋转激活情况的大多数区域，激活量都有所减少。然而，仅在下外侧小脑且仅对于110度操纵杆，激活量在边缘显著水平（p < 0.08）上有所增加。在大脑皮层中，与110度相关的激活在前额叶和顶叶区域减少，但在运动前区和辅助运动区（SMA）区域增加。这些结果可以用一个模型来解释，即在25分钟训练之前，60度和160度内部模型的输出由前额叶和顶叶区域融合以应对新的110度操纵杆；在小脑中获取110度的内部模型后，输出直接发送到运动前区和SMA区域，并且这些区域的激活增加。
