Relationship between lower limb function and functional connectivity assessed by EEG among motor-related areas after stroke.

Background : Neural connectivity in brain has been known as indicators for neural function and recovery of brain. Although previous studies reported that neural connectivity predicted the recovery of upper limb function after stroke, the relationship between neural connectivity and lower limb function has not been clear. Objectives : To clarify whether functional connectivity (FC) assessed by electroencephalographiy (EEG) with five electrodes placed on motor-related areas could be related to the functional motor recovery of the lower limbs in patients after stroke. Methods : Twenty-four patients with stroke during the recovery phase were recruited. Motor function of the lower limbs was assessed using Fugl-Meyer Assessment lower limb section (FMAL). EEG signals were recorded by five electrodes (C3, C4, FC3, FC4, and FCz) at rest and during ankle movement. Amplitude envelope correlations, as values for FC, were calculated in α (8-12 Hz), β (13-30 Hz), low-β (13-19 Hz), and high-β (20-30 Hz) frequency bands. The predictive regression equation of the FMAL score in the eighth week after stroke (8 W) was created by FCs in the fourth week (4 W). Results : The higher intra-hemispheric FC in both hemispheres in the resting state and during the ankle movement at 4 W was related to a higher lower limb function at 8 W. Additionally, the higher inter-hemispheric FC between M1 on both sides during the ankle movement was related to a higher function recovery. Conclusions : The intra- and inter-hemispheric FC among motor-related areas at 4 W after stroke might be related to the functional recovery of the lower limbs at 8 W.