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

灵长类体感侏儒表征的最突出特征之一是手面边界。减少或消除来自面部或手部的体感输入会导致跨界重组，就像在截肢者身上观察到的那样。由于这种重组与皮层区域的得失有关，并与消极的感知后果并行，因此通常认为它是竞争性的，皮层区域侵入缺乏输入的邻近区域。然而，哪些机制在正向可塑性过程中起作用仍有待澄清，正向可塑性发生在传入输入增强的条件下，并导致感知和感觉运动表现的改善。为了解决这个问题，有必要通过控制传入输入来系统地操纵大脑的可塑性。最近的研究表明，除了训练和练习之外，训练独立的重复性感觉刺激（RSS）还可以诱导大脑的可塑性，从而提高受刺激手指的触觉表现并扩大其体感表征。在一项包括法国和德国团队的初步研究中，我们发现手指上的RSS不仅改变了手指的触觉表现，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感知学习现象的存在：感知改善在手-脸边界的转移，并表明跨界可塑性不仅仅是竞争性的。这一建议建立在这一发现的基础上，系统地研究了在完整传入流入条件下人类跨界可塑性的特性和机制。本实验旨在研究知觉和感觉运动学习、跨界迁移和相关皮层重组的特性。具体而言，我们将研究手指或嘴唇刺激后体感觉系统的皮层重组，手指刺激对手/口运动协调的影响，以及可塑性变化对Hebbian学习规则的依赖性。为了研究生态条件下（无RSS）跨界可塑性的影响，我们将研究感官能力增强或受损的亚种群的指唇表现。这个项目将增加我们对大脑组织动态维护的机制的理解，以及在生理和病理条件下伴随感觉学习的过程。所产生的知识将对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据此采取行动，控制人类感觉系统的动态平衡的调节过程。

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.