Brain Symmetry Index in Healthy and Stroke Patients for Assessment and Prognosis

Abstract

Objective. Quantitative neurophysiological signal parameters are of value in predicting motor recovery after stroke. The novel role of EEG-derived brain symmetry index for motor function prognostication in the subacute phase after stroke is explored. Methods. Ten male stroke patients and ten matched healthy controls were recruited. Motor function was first assessed clinically using the MRC score, its derivative Motricity Index, and the Fugl-Meyer assessment score. EEG was subsequently recorded first with subjects at rest and then during hand grasping motions, triggered by visual cues. Brain symmetry index (BSI) was used to identify the differences in EEG-quantified interhemispheric cortical power asymmetry observable in healthy versus cortical and subcortical stroke patients. Subsequently, any correlation between BSI and motor function was explored. Results. BSI was found to be significantly higher in stroke subjects compared to healthy controls (p = 0.023). The difference in BSI was more pronounced in the cortical stroke subgroup (p = 0.016). BSI showed only a mild general decrease on repeated monthly recording. Notably, a statistically significant correlation was observed between early BSI and Fugl-Meyer score later in recovery (p < 0.050). Conclusions. Brain symmetry index is increased in the subacute poststroke phase and correlates with motor function 1-2 months after stroke.

Figure 1

Brain symmetry index (BSI) scores obtained during (a) rest task (Task 1) with eyes either closed (BSI_c) or open (BSI_o) and during (b) paretic and (c) nonparetic hand grasping tasks (Task 2). Data is from session 1 of all 20 subjects, separated into healthy (blue), cortical (striped green), and subcortical (light yellow) stroke.

Figure 2

Correlation of brain symmetry index at rest recorded during the first session (BSI_c1) with (a) Motricity Index in the first (MI1, blue) and second session (MI2, green) and with (b) Fugl–Meyer in the first (FM1, blue) and second session (FM2, green).

Figure 3

Correlation of Fugl–Meyer recorded in the second session (FM2) against original BSI in the first session (BSI_c1, blue) and BSI recorded in the second session (BSIc2, green).

Figure 4

FM and MI improvement versus BSIc1 for patients who had at least 2 assessment sessions.

Figure 5

BSIc1 of all 20 subjects recruited. “Stroke patients with no recorded FM improvements” may be either due to lack of follow-up (s06–s09) or because FM1 was already 66 (s01).

Figure 6

Brain symmetry index in session 1 (BSIc1) from all 20 subjects, against their Fugl–Meyer score both in session 1 (yellow bubble for stroke patients and green bubble for healthy controls) and in session 2 (red bubble) when this was present. The blue arrow and score represents the Fugl–Meyer improvement (FMI) for those who had a second (follow-up) session.