Learning and plasticity in the human brain

这项研究的主要目标是：1)建立神经系统损伤或功能障碍引起的大脑处理的变化；2)了解大脑的可塑性如何促成这些变化；3)确定学习如何改善这些变化的负面后果。在过去的一年里，在失去了对大脑特定区域的输入后，我们继续主要关注可塑性，包括视觉和躯体感觉皮质。 I)失去视觉输入。黄斑变性患者由于视网膜损伤而丧失中心视力。但大脑中专门负责处理中央视觉刺激的部分会发生什么呢？使用功能磁共振成像，我们之前已经表明，大脑中被剥夺输入的部分开始对视野中其他区域的视觉刺激做出反应，就像它们正在承担新的功能一样。我们把这称为视觉处理的重组。我们进一步证明，这种重组依赖于中心视力的完全丧失，并不特定于黄斑变性患者用于固定的视网膜部分(通常被称为首选视网膜位置，或PRL)，并可能导致知觉扭曲。我们目前正在研究黄斑变性患者视力丧失对皮质厚度的影响。据报道，在一些发育性视觉障碍中，大脑皮质比健康对照组参与者更薄，但尚不清楚当成年后视力丧失时，这种结构变化是否也会发生。 Ii)失去躯体感觉输入。截肢后，超过90%的人报告说他们失去的肢体有幻觉，通常是疼痛的感觉(幻肢疼痛，或PLP)。一种目前的理论认为，PLP是皮质重组的直接结果，这是不适应可塑性的一个例子。镜像疗法已被用于PLP的治疗。在这种治疗过程中，患者在照镜子的同时移动他们完整的肢体，使他们失去的肢体看起来像是在移动。我们目前正在研究截肢的神经后果，以及随着时间的推移，镜像疗法对大脑活动的影响。我们继续招募单侧肢体截肢者，并在截肢者接受镜面治疗期间，在四周内用功能磁共振监测大脑活动。我们正试图确定PLP的存在是否与躯体感觉和运动皮质的皮质重组有关(类似于我们在黄斑变性患者中观察到的情况)，以及镜像疗法是否通过减少皮质重组的程度而起作用。 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 the changes in brain processing arising from nervous system damage or dysfunction, ii) to understand how brain plasticity contributes to these changes, and iii) to determine how learning may ameliorate the negative consequences of such changes. Over the past year we have continued to focus primarily on plasticity following the loss of input to particular regions of the brain, including visual and somatosensory cortex. i) Loss of visual input. People with macular degeneration lose central vision due to retinal damage. But what happens to the parts of the brain that are specifically involved in processing central visual stimuli? Using fMRI, we have previously shown that the parts of the brain deprived of input start to respond to visual stimuli in other regions of the visual field, as if they are taking on new function. We have referred to this as reorganization of visual processing. We have further demonstrated that such reorganization is dependent on complete loss of central vision, is not specific to the part of the retina used for fixation in people with macular degeneration (often referred to as the Preferred Retinal Locus, or PRL), and may lead to perceptual distortions. We are currently investigating the impact of vision loss in macular degeneration on cortical thickness. In some developmental visual disorders, the cortex has been reported to be thinner than in healthy control participants, but it is unknown whether such structural changes also occur when the vision loss happens in adulthood. ii) Loss of somatosensory input. Following limb amputation, over 90% of people report phantom sensations in their missing limb, often painful sensations (Phantom Limb Pain, or PLP). One current theory suggests that PLP is a direct result of cortical reorganization, an example of maladaptive plasticity. Mirror therapy has been used as a treatment for PLP. During this therapy, patients move their intact limb while looking in a mirror, making it seem as if their missing limb is moving. We are currently investigating the neural consequences of amputation and the impact of mirror therapy on brain activity over time. We are continuing to recruit unilateral limb amputees and monitoring brain activity with fMRI over a period of four weeks while the amputees undergo mirror therapy. We are trying to establish whether the presence of PLP correlates with cortical reorganization in the somatosensory and motor cortex (similar to that observed in our participants with macular degeneration) and whether the mirror therapy works by reducing the extent of cortical reorganization. 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.