Abstract

The ratio between slower and faster frequencies of brain activity may change after stroke. However, few studies have used quantitative electroencephalography (qEEG) index of ratios between slower and faster frequencies such as the delta/alpha ratio (DAR) and the power ratio index (PRI; delta + theta/alpha + beta) for investigating the difference between the affected and unaffected hemisphere poststroke. Here, we proposed a new perspective for analyzing DAR and PRI within each hemisphere and investigated the motor impairment-related interhemispheric frequency oscillations. Forty-seven poststroke subjects and twelve healthy controls were included in the study. Severity of upper limb motor impairment was classified according to the Fugl–Meyer assessment in mild/moderate (n = 25) and severe (n = 22). The qEEG indexes (PRI and DAR) were computed for each hemisphere (intrahemispheric index) and for both hemispheres (cerebral index). Considering the cerebral index (DAR and PRI), our results showed a slowing in brain activity in poststroke patients when compared to healthy controls. Only the intrahemispheric PRI index was able to find significant interhemispheric differences of frequency oscillations. Despite being unable to detect interhemispheric differences, the DAR index seems to be more sensitive to detect motor impairment-related frequency oscillations. The intrahemispheric PRI index may provide insights into therapeutic approaches for interhemispheric asymmetry after stroke.

Highlights

  • Stroke is one of the leading causes of adult disability worldwide [1]

  • The abnormal interhemispheric interaction after a brain injury has been mainly investigated by functional magnetic resonance imaging, positron emission tomography (PET), and transcranial magnetic stimulation (TMS) [5, 6]

  • The presence of lowfrequency oscillations in the EEG signal is linked to the decline in neuronal integrity [7, 8], whereas the presence of fast-frequency oscillations after stroke is associated with the motor recovery and functional outcome following stroke [7, 9]

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Summary

Introduction

Stroke is one of the leading causes of adult disability worldwide [1]. Following a stroke, an imbalance in the interhemispheric cortical interaction may be established [2]. The ability to perform skilled limb movements requires a dynamic interaction between the hemispheres. Maladaptive functioning of this interhemispheric interaction and changes in hemisphere neural activity after stroke are thought to be factors underlying motor impairments and the poorest motor recovery in these patients [3,4,5]. The presence of lowfrequency oscillations (delta and theta rhythm) in the EEG signal is linked to the decline in neuronal integrity [7, 8], whereas the presence of fast-frequency oscillations (alpha, beta, and gamma rhythm) after stroke is associated with the motor recovery and functional outcome following stroke [7, 9]. The qEEG index of ratio between slower and faster frequencies such as the delta/alpha ratio (DAR) [10], the power ratio index (PRI; delta + theta/alpha + beta) [11, 12], Neural Plasticity and the theta/beta ratio (TBR) [13, 14] has been largely employed in stroke studies [10, 13, 15,16,17,18,19]

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