Cortical Plasticity and Motor Activity Studied with Transcranial Magnetic Stimulation

Abstract

For decades cortical representations of the parts of the body have been considered to be unchangeable. This view has changed radically during the past 20 years using new tools designed to study plasticity in the adult human brain. Transcranial magnetic stimulation (TMS) is a valuable non-invasive technique for exploring the ability of the motor cortex to change during motor skill acquisition. Results obtained with TMS in neurological patients as well as in normal subjects demonstrate that cortical plasticity is a necessity for correct adaptation to the continuously changing environment. Topographical reorganization of the motor cortex depends on the types of movements performed by the subjects. During simple training, the cortical representation is enlarged, and it returns to its initial size when the task is overlearned. These transient modifications characterize simple motor training. Motor skills in which coordination of distal and proximal muscles, precision of the task and spatio-temporal constraints are associated, has a different impact on cortical reorganization. We propose that years of practice of a complex motor skill induces a new cortical topography that must be interpreted as structural plasticity which provides the capacity to execute a plastic behaviour instead of a stereotypical movement. We review the neuronal mechanisms underlying plasticity in different types of movement. We stress new emerging notions, such as overlap of cortical maps, and system dynamics at single neuron and network levels, to explain the reorganization of movement representations that encode motor skill. Dendritic arborizations as functional computing elements, newly generated neurons in adult brain, and plastic architectures of cortical networks operating as distributed functional modules are new hypotheses for structural plasticity.

Cortical overlap of joint representations contributes to the loss of independent joint control following stroke

“…Such abnormal muscle co-activation pattern in the paretic limb may be due to an abnormal increase in the overlap of cortical representation for elbow and shoulder joint/muscles. Evidence for cortical overlap of joint/muscles representations has been provided by results in both animals (Clark et al, 1988; Godde et al, 1996; Gribble and Scott, 2002; Hoffer et al, 2005; Rathelot and Strick, 2006) and human subjects (Cramer et al, 2003; Devanne et al, 2006; Godde et al, 1996; Marconi et al, 2007; Melgari et al, 2008; Schabrun and Ridding, 2007; Singh and Scott, 2003; Tyc and Boyadjian, 2006). It has been suggested that such overlaps may be the neural substrate to create a wide variety of functional muscle synergies (Melgari et al, 2008; Rathelot and Strick, 2006).…”

Localised muscle pain and dysfunction: a review of theoretical and suppositional biological effects of jaw exercises

“…However, current knowledge indicates "the neuro-muscular system from brain to muscles is plastic" [145]. Finally, compared to the huge knowledge about biological effect of exercises in healthy neuro-muscular system (e.g.…”

“…Innumerable studies show that muscle activity but also muscle hypoactivity have multiple effects [155] on: (1) motor controlneurophysiological effects [29,30,38,44,161], and spinal and cortical neuroplasticity [1,126,145,157,158] (recently face motor cortex plasticity has also been reviewed [131]); (2) hemodynamics (see refs. below); (3) histological parameters (phenotypic conversion and change of size/number -i.e., hypertrophy/hyperplasia, respectively -of muscle fibres, and exercise-induced capillary angiogenesis -see refs.…”

Repetitive Transcranial Magnetic Stimulation for Clinical Applications in Neurological and Psychiatric Disorders: An Overview

“…TMS is based on Faraday's law of electromagnetic induction, by which electrical activity in the brain tissue can be influenced by the magnetic field, thereby inducing electrical current that depolarizes neurons [2,9]. The application of rTMS generates clear effects on a range of measures of brain function and has become an important research tool due to its potential application as a clinical treatment for a variety of neurological and psychiatric disorders, for instance, depression [2,[10][11].…”