Dynamic Hemispheric Lateralization of Naturalistic Emotional Processing After Unilateral Stroke: An EEG Study

Emotional impairment is common after stroke, but the neural electrophysiological mechanisms by which left- and right-hemisphere lesions differentially alter emotional processing remain unclear. Conventional time-averaged measures may overlook its dynamic features in the temporal organization of emotional processing. This study aimed to characterize hemisphere-group-associated differences in dynamic hemispheric lateralization during naturalistic emotional processing after unilateral stroke.

In this cross-sectional study, 15 patients with left-hemisphere stroke (L-stroke), 15 patients with right-hemisphere stroke (R-stroke), and 15 healthy controls viewed validated positive, neutral, and negative film clips during 64-channel electroencephalography recording. Self-Assessment Manikin ratings were collected after each clip. We computed spectral power, emotion-averaged lateralization index (LI), inter-clip LI stability, and within-clip LI dynamics (detectability, switching rate, and entropy). Mixed-effects models accounted for repeated observations within participants and, where applicable, variability across film clips.

Stroke patients showed reduced valence and arousal responses to positive clips, particularly in R-stroke patients. Low-frequency spectral power analysis showed preserved emotion modulation, whereas emotion-averaged LI mainly reflected group-dependent hemispheric bias. Within-clip parietal-theta LI dynamics revealed hemispheric differences: L-stroke showed higher detectability and lower switching, while R-stroke showed increased switching and entropy during positive clips. Switching showed a group-dependent association with arousal in the primary model, with stronger coupling in R-stroke.

Dynamic parietal-theta lateralization revealed hemisphere-group-associated differences in the stability-flexibility balance of emotional brain states that were not captured by time-averaged measures. These findings suggest that parietal-theta LI dynamics may provide a preliminary candidate electrophysiological feature for characterizing post-stroke emotional dysfunction.