Learning and plasticity in the human brain

这项研究的主要目标是：1)确定学习如何影响大脑的结构和功能；2)确定学习如何受到反馈(积极或消极)等因素的影响。在过去的一年里，我们同样关注这两个目标。 1)学习对大脑结构和功能的影响(NCT00001360) 在过去的几年里，我们一直在对学习不同任务(例如运动序列、空间布局)的参与者进行长期的纵向研究，以确定大脑(灰质、白质)的结构属性如何随时间变化。在四周的时间里，参与者接受了两项不同任务的培训，我们在培训过程中收集了大量的功能和结构磁共振数据。 虽然之前的研究已经发现了与学习相关的结构性变化，即使是在几个小时的过程中，我们的初步发现也突显了一个潜在的困惑，需要在这类研究中加以考虑。具体地说，我们发现MRI获得的结构性测量结果会随着时间的不同而波动，灰质厚度减少，脑室容量增加。这些波动似乎与大脑中脑脊液的变化有关，可能反映了日常昼夜节律的影响。 有趣的是，这些波动似乎受到训练的调节，我们正试图确定训练除了这些时间影响之外，还会发生哪些额外的结构和功能变化。对于运动序列任务，我们发现，在训练之后，感觉运动网络显示出其功能连接性的变化。相比之下，随着空间布局任务的完成，海马区网络发生了变化。这些发现表明，特定网络中特定任务的变化是学习的基础，而不是由于昼夜波动造成的任何变化。 2)反馈对学习的影响(NCT00001360) 我们正在调查反馈(积极的、消极的)对运动学习的影响。一组参与者接受了两种不同运动任务中的一种的训练，并得到积极、消极或中性(无信息)的反馈。训练在MRI扫描仪上进行，我们在训练前、训练中和训练后测量fMRI活动。 在行为上，我们发现反馈的影响取决于任务。在顺序学习任务中，我们发现惩罚提高了在线表现，而在纯运动力跟踪任务中，我们观察到了相反的效果。 在大脑活动方面，我们发现惩罚更多地与内侧颞叶和海马体的变化有关，而奖励更多地与小脑的变化相关。这些发现表明，奖励和惩罚的影响背后的神经机制可能被用来加强训练。 建立成人大脑皮质可塑性的性质、程度和后果，为神经系统损伤或功能障碍后康复脑治疗的可能性提供重要的见解。

The primary goals of this research are i) to establish how learning impacts the structure and function of the brain, and ii) to determine how learning can be modulated by factors such as feedback (positive or negative). Over the past year we have focused equally on both of these goals. 1) Impact of learning on brain structure and function (NCT00001360) Over the past few years, we have been conducting a long-term longitudinal study of participants learning different tasks (e.g. motor sequences, spatial layout) to determine how structural properties of the brain (gray matter, white matter) change over time. Over a period of four weeks, participants were trained in two different tasks and we collected extensive functional and structural MRI data over the course of training. While previous studies have identified structural changes associated with learning, even over the course of a couple of hours, our initial findings have highlighted a potential confound that needs to be accounted for in such studies. Specifically, we have found that the structural measures obtained with MRI fluctuate according to the time of day, with decreases in gray matter thickness and increases in ventricular volume. These fluctuations appear to be related to changes in cerebrospinal fluid in the brain and may reflect the impact of the daily circadian rhythm. Interestingly, these fluctuation appear to be modulated by training and we are trying to establish what additional structural and functional changes occur with training above and beyond these time-of-day effects. With the motor sequence task we find that, following training, sensorimotor networks show changes in their functional connectivity. In contrast, with the spatial layout task, hippocampal networks change. These findings suggest task-specific changes in particular networks underlie learning above and beyond any changes due to circadian fluctuations. 2) Impact of feedback on learning (NCT00001360) We are investigating the impact of feedback (positive, negative) on motor learning. Groups of participants were trained on one of two different motor tasks and either provided with positive, negative or neutral (uninformative) feedback. Training occurred in the MRI scanner and we measured fMRI activity before, during and after training. Behaviorally, we found that the impact of feedback is dependent on the task. While in a sequence learning task we find that punishment improves online performance, we observe the opposite effect in a purely motoric force-tracking task. In terms of brain activity, we found that punishment was more associated with changes in the medial temporal lobe and hippocampus, while reward was more associated with changes in the cerebellum. These findings suggest a dissociation of the neural mechanisms underlying the impact of reward and punishment that might be utilized to enhance training. Establishing the nature, degree and consequences of plasticity in the adult cortex provides important insights into the potential for rehabilitative brain therapies following injury or dysfunction in the nervous system.