Motor Control and Neural Plasticity through Interhemispheric Interactions

Only 8 pages for your doctor to figure out how this is going to help you recover.  Your doctor DOES NOTHING with this? Then you don't have a functioning stroke doctor

 Motor Control and Neural Plasticity through Interhemispheric Interactions

 Naoyuki Takeuchi,YutakaOouchida, andShin-IchiIzumi
Department of Physical Medicine and Rehabilitation, Tohoku University Graduate School of Medicine, 2-1 Seiryo-Cho, Aoba-Ku, Sendai 980-8575, Japan
Correspondence should be addressed to Naoyuki Takeuchi, naoyuki@med.hokudai.ac.jpReceived 5 September 2012; Revised 16 November 2012; Accepted 3 December 2012Academic Editor: Maurice PtitoCopyright © 2012 Naoyuki Takeuchi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

The corpus callosum, which is the largest white matter structure in the human brain, connects the 2 cerebral hemispheres. It plays a crucial role in maintaining the independent processing of the hemispheres and in integrating information between both hemispheres. The functional integrity of interhemispheric interactions can be tested electrophysiologically in humans by using transcranial magnetic stimulation, electroencephalography, and functional magnetic resonance imaging. As a brain structural imaging, diffusion tensor imaging has revealed the microstructural connectivity underlying interhemispheric interactions. Sex,age, and motor training in addition to the size of the corpus callosum influence interhemispheric interactions. Several neurological disorders change hemispheric asymmetry directly by impairing the corpus callosum. Moreover, stroke lesions and unilateral peripheral impairments such as amputation alter interhemispheric interactions indirectly. Noninvasive brain stimulation changes the interhemispheric interactions between both motor cortices. Recently, these brain stimulation techniques were applied in the clinical rehabilitation of patients with stroke by ameliorating the deteriorated modulation of interhemispheric interactions.Here, we review the interhemispheric interactions and mechanisms underlying the pathogenesis of these interactions and propose rehabilitative approaches for appropriate cortical reorganization.

1.Introduction

The corpus callosum, which is the largest white matter structure in the human brain, connects the homologous and nonhomologous areas of the 2 cerebral hemispheres[1, 2]. It plays a crucial role in the interhemispheric interactions that maintain independent processing and integrate information between both hemispheres [2, 3]. The functional integrity of interhemispheric interactions can be tested electrophysiologically in humans using single-pulse transcranial magnetic stimulation (TMS), double-pulse TMS, and electroencephalography  [4–8]. These electrophysiological techniques were used to estimate inter-hemispheric transmission times (from 4 to 50ms) [1, 3]. Structural studies using diffusion tensor imaging (DTI)have revealed the microstructural connectivity underlying interhemispheric interactions [9–12]. Moreover, functional magnetic resonance imaging (fMRI) studies have revealed interhemispheric interactions using resting-state functional and activity dependent effective connectivity analyses [13,14]. Research on the functions of interhemispheric interactions is based on studies of brain lateralization, which is thought to allow each hemisphere to process information without the interference of the contralateral hemisphere[15,16]. Several studies have suggested that the speed of transcallosal conduction is limited in larger brains, which implies that the transfer and integration of information between both hemispheres through the corpus callosum require more time and energy in humans [3, 17]. Therefore, it may  be more efficient to use one hemisphere and inhibit the other hemisphere during simple tasks (e.g., physical identity and face-matching tasks); this promotes intrahemispheric processing and brain lateralization [2, 18, 19].