Inhibition of the contralesional hemisphere after stroke: reviewing a few of the building blocks with a focus on animal models

The last decade of neuroscience research has revealed that the adult brain can undergo substantial reorganization following injury. Plasticity after stroke has traditionally been perceived as adaptive and supporting recovery, but recent studies have suggested that some plasticity may also be detrimental. In particular, increased activity in the unaffected (contralesional) hemisphere has been proposed to contribute to motor deficits of the paretic hand in some patients. Longitudinal imaging studies in humans have reported a progressive behavioral improvement associated with a decrease of contralesional activity and have correlated the intensity of contralesional hemisphere activity with the degree of motor impairment. Consequently, inhibitory neuromodulatory protocols have been applied to the contralesional hemisphere of stroke patients. Such protocols can facilitate the activation of the ipsilesional motor cortex and improve the function of the paretic limb. Although the use of noninvasive techniques after brain injury shows promise, much work needs to be done to understand better how these approaches affect postlesion plasticity and motor recovery. Ultimately, this knowledge will allow for the design of more effective treatments and will potentially lead to protocols adapted to the specific condition of each patient. In this chapter, we review the literature on the basic pathways that can support the effects of contralesional inhibition, interhemispheric interactions, and some of the changes that can occur in the sensorimotor network after stroke. Finally, we show work in rats that demonstrates how parameters of contralesional inactivation can affect postlesion recovery.