The role of EEG as a biomarker tool in assessing plastic chances induced by transcranial magnetic stimulation in stroke patients

Abstract

Stroke is the leading cause of long-term disability. It occurs when the blood supply to the brain is disrupted by cerebrovascular disease, which can lead to permanent damage, depending on the duration and extent. After stroke, neuroplasticity occurs and this is one of the main factors that one could potentially use to overcome the caused damage. One of the techniques which has been able to modulate the brain’s plasticity and has been achieving promising results is transcranial magnetic stimulation (TMS). In this study we used the continuous theta burst stimulation (cTBS), a protocol that inhibits the hemisphere in which it is applied, so that the other hemisphere becomes more excited. We had two main objectives in this study, first to characterize physiological patterns in healthy subjects and then to study their potential relevance in the context of stroke. For one session, cTBS was delivered over the unaffected hemisphere of the patient. Healthy subjects were divided in two groups: one group received the cTBS protocol on the left hemisphere and the other group received it on the contralateral hemisphere. Thus, the aim of this study is to understand the brain’s physiology before and after cTBS, to provide a possible rehabilitation approach to stroke patients with motor deficits; the other aim is to know if the cTBS protocol when applied on the dominant or the non-dominant hemisphere has the same results. To understand the brain’s changes before and after the TMS we used the electroencephalogram (EEG). EEG at high recording density was used to evaluate the brain’s activity at rest and to analyze the event-related desynchronization (ERD) and synchronization (ERS) of electrophysiological motor biomarkers (e.g. mu rhythm, beta activity) when the subjects performed two different types of movements, one with arms and the other with hands. Our results showed that cTBS affected the brain’s physiology and biomarkers of motor activity. When applied to the dominant or non-dominant hemisphere cTBS protocol has showed different aftereffects. For the stroke patients the results were matched to one control that received cTBS on the same hemisphere. The patient and the matched-control showed similar results for complex movements (hand tasks); while, for simpler movements (arm tasks) they behaved differently, except for the right arm. We hypothesized that this difference on the arm tasks results could have occurred because the patient activated brain areas that are normally recruited in more demanding tasks. Despite the results observed it will be needed more patients and additional studies to have more reliable conclusions