Abstract #161: When stimulating the unaffected (healthy) hemisphere in stroke patients makes sense

Abstract

Research investigating the use of noninvasive electrical stimulation (e.g., transcranial direct current stimulation (tDCS)) has provided compelling evidence that such stimulation can modulate sensorimotor function, behavior and cognition, and even facilitate recovery of function after a focal brain injury. Our understanding of the mechanisms that lead to such changes is limited, and the influence of variables such as current strength, electrode montage and which regions of the brain to target is the focus of ongoing investigations. The degree of structural and/or functional injury to relevant systems (e.g., hand-motor system, speech-motor system, and swallowing system) and their pathways has been shown to determine natural outcome after a stroke and the response to an experimental intervention. However, the degree of bihemispheric organization of these systems and how redundant a system is organized in the brain seems to contribute to how well a particular system recovers. The premorbid organizational structure might also affect neuroplasticity, since plastic changes such as changes in synapses, axonal sprouting, changes in myelination, could affect the lesional and peri-lesional region as well as homotop regions of the contralesional hemisphere. Plasticity-enhancing tools might have an additive effect, although there are potentially multiple targets depending on the systems organizational structure. tDCS has been shown to modulate motor cortical excitability, modify a stroke-induced abnormal imbalance in inter-hemispheric inhibition, and increase synaptic plasticity if combined with a peripheral rehabilitation therapy. In this talk I will present the responses of different systems in the brain, contrasting a system that is more unihemispherically organized and has less redundancy and with a system that is more bihemispherically organized and has more redundancy. A redundant system has more options for targeted stimulation and electrode montages than a non-redundant system.