Breaking the boundaries of brain plasticity: adaptive plasticity across the hand-face border

灵长类躯体感觉侏儒表征的最显著特征之一是手-脸边界。减少或消除来自面部或手部的躯体感觉输入会导致跨界重组，就像在截肢者中观察到的那样。由于这种重组与皮层区域的收益/损失有关，并且受到负面感知后果的影响，因此通常认为它是竞争性的，皮层区域侵入了被剥夺输入的邻近区域。然而，还有待澄清的是，哪些机制在积极的可塑性，这发生在增强的传入输入的条件下，并导致改善的知觉和感觉运动performance.To解决这个问题，它是必不可少的系统操纵大脑可塑性通过操纵传入输入。最近的研究表明，除了训练和练习，大脑可塑性可以通过训练无关的重复感觉刺激（RSS）来诱导，这可以提高受刺激手指的触觉表现并扩展其体感表征。在一项涉及法国和德国团队的初步研究中，我们发现手指上的RSS不仅改变了这个手指的触觉表现，而且还改变了上唇的触觉表现。这些结果揭示了一种以前未知的知觉学习现象的存在：知觉改善跨越手脸边界的转移，并表明跨界可塑性不仅具有竞争性。该提议通过系统地研究跨界可塑性的性质和机制建立在这一发现的基础上。在完整的传入流入条件下，人类的边界可塑性。拟议的实验研究知觉和感觉运动学习，跨界转让，以及相关的皮层重组的属性。具体来说，我们将调查皮层重组的躯体感觉系统后，手指或嘴唇刺激，手指刺激的影响，手/口运动协调，和依赖性的赫布学习规则的塑料变化。为了研究在生态条件下（无RSS）的跨界可塑性的影响，我们将研究手指-嘴唇的表现在一个选择的亚群，无论是增强或受损的感觉能力。这个项目将增加我们的理解的机制，大脑组织的动态维护和过程中伴随的生理和病理条件下的感觉学习。所产生的知识将为系统和行为神经科学领域做出重大贡献，因为它将使我们能够识别并可能采取行动，管理人类感觉系统稳态的调节过程。

One of the most prominent features of the primate somatosensory homuncular representation is the hand-face border. Reducing or eliminating somatosensory input from either the face or the hand results in cross-border reorganisation like that observed in amputees. Since this reorganisation is associated with gains/losses in cortical territory and is paralleled by negative perceptual consequences, it is generally assumed to be competitive, with cortical territory invading input-deprived neighbouring areas. It remains to be clarified, however, which mechanisms operate during positive plasticity, which occurs under conditions of enhanced afferent inputs and results in improved perception and sensorimotor performance.To address this question it is essential to systematically manipulate brain plasticity by manipulating afferent inputs. Recent research has shown that besides training and practicing, brain plasticity can be induced by training-independent repetitive sensory stimulation (RSS), which improves tactile performance at the stimulated finger and expands its somatosensory representation. In a preliminary study involving both the French and German teams we found that RSS on the finger altered tactile performance not only at this finger but also at the upper-lips. These results reveal the existence of a previously unknown perceptual learning phenomenon: the transfer of perceptual improvement across the hand-face border, and suggest that cross-border plasticity is not only competitive.This proposal builds upon this finding by systematically investigating the properties and mechanisms of cross-border plasticity in humans under conditions of intact afferent inflow. The proposed experiments investigate the properties of perceptual and sensorimotor learning, cross-border transfer, and the associated cortical reorganization. Specifically, we will investigate cortical reorganization in the somatosensory system following either finger or lip stimulation, the impact of finger stimulation on hand/mouth motor coordination, and the dependency of plastic changes on Hebbian learning rules. To investigate the impact of cross-border plasticity under ecological conditions (without RSS), we will study finger-lip performance in a selection of subpopulations with either enhanced or impaired sensory abilities.This project will increase our understanding of the mechanisms underlying the dynamic maintenance of brain organisation and the processes accompanying sensory learning in physiological and pathological conditions. The knowledge generated will make a substantial contribution to the domain of systems and behavioural neuroscience as it will allow us to identify and possibly act upon, the regulatory processes governing homeostasis of the human sensory system.