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

灵长类躯体感觉人形表征最显著的特征之一是手脸边界。减少或消除面部或手部的体感输入会导致跨境重组，就像截肢者所观察到的那样。由于这种重组与大脑皮层领域的得失相关，并伴随着负面感知后果，因此通常被认为是竞争性的，大脑皮层领域侵占了投入匮乏的邻近地区。然而，哪些机制在正性可塑性中起作用仍有待阐明，正性可塑性发生在增强的传入输入条件下，并导致感知和感觉运动性能的改善。为了解决这个问题，必须通过操纵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，非训练依赖的重复感觉刺激(RSS)可以诱导大脑的可塑性，它可以改善受刺激手指的触觉表现，并扩大其体感表征。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不仅改变了手指的触觉表现，也改变了上嘴唇的触觉表现。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，并表明跨境可塑性不仅是竞争性的。本研究基于这一发现，系统地研究了在完整传入流入条件下人类跨境可塑性的性质和机制。该实验研究了知觉和感觉运动学习、跨境迁移和相关的大脑皮层重组的特性。具体地说，我们将研究手指或嘴唇刺激后躯体感觉系统中的皮质重组，手指刺激对手/嘴运动协调的影响，以及塑料变化对Hebbian学习规则的依赖。为了研究生态条件(没有RSS)下跨界可塑性的影响，我们将研究一组感觉能力增强或受损的亚群的指唇行为。这个项目将增加我们对大脑组织动态维持的机制以及在生理和病理条件下伴随感觉学习的过程的理解。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采取行动，管理人类感觉系统的自稳调节过程。

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.