Abstract
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.
Highlights
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]
transcranial magnetic stimulation (TMS) studies have showed that interhemispheric inhibition persisted from the unaffected to the affected hemisphere around the onset of the movement of the paretic hand in stroke patients, whereas the interhemispheric interaction in healthy controls changed from inhibitory to excitatory influence on the active motor cortex closer to the time of movement onset [34, 98]
This paper focused on the mechanisms underlying motor control and neural plasticity that relate to interhemispheric interactions to suggest approaches for appropriate cortical reorganization
Summary
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 singlepulse transcranial magnetic stimulation (TMS), doublepulse TMS, and electroencephalography [4,5,6,7,8]. 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]. The purposes of this paper were to provide a comprehensive overview of motor interhemispheric interactions to promote the understanding of their underlying mechanisms and to suggest approaches for appropriate neural plasticity
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