Mechanisms of experience-induced brain plasticity in the adult speech system

点击翻译按钮获取中文摘要

Speaking is a remarkably complex human action whose neural architecture is still only partly understood. Despite tremendous progress in understanding the neural speech system, several questions remain regarding the organization of this system, its relationship to speech performance, and, importantly, its evolution over the adult lifespan. Despite a normal decline of structure and functions with age, the healthy adult brain retains a remarkable capacity to modify its structure and organization across the entire lifespan, following the acquisition of new skills, such as learning to speak a new language or to play a new instrument. This phenomenon is known as experience-dependent brain plasticity. In addition to skill learning, another method to induce brain plasticity is through the use of a device called "repetitive transcranial magnetic stimulation" or rTMS. rTMS delivers magnetic stimulation to specific brain areas and can modify their functioning, which can enhance behaviour. The objective of this research program is to better understand the neurobiology of the adult speech system by investigating how age and different kinds of experience can change the anatomy and functioning of the speech system. To achieve this general objective, a series of studies will be conducted. The first set of studies will focus on optimizing a rTMS protocol to enhance speech production by inducing plasticity in different regions of the speech system. Because brain stimulation technologies are not yet optimized for the study of speech, we will test different protocols for inducing plasticity in the speech system and identify the one that produces the most significant changes in younger and older adults. Using the knowledge generated in these studies, we will conduct a longitudinal speech training study consisting in learning to produce and perceive new speech sounds. Three groups of healthy adults will be recruited. One group will receive only the speech training. The second group will receive only rTMS. The third group will receive both. It is expected that the group receiving both rTMS and the speech training will show the most evidence of plasticity, behaviourally (enhanced speech performance) and in the brain, measured using magnetic resonance imaging (MRI). Behavioural and MRI measurements will be made at the beginning of the training, after 4 weeks and after 8 weeks, allowing us to examine the time course of behavioural and brain changes. This research program will advance current knowledge of experience-induced plasticity mechanisms in the healthy human brain. The proposed program will also contribute significantly to theories and knowledge about the neural speech system. Finally, the knowledge generated as part of the program will contribute to the development of brain-enhancing technologies and cognitive stimulation applications, which are being developed and patented across the world in the absence of adequate scientific and theoretical support.