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, suggesting that parietal-theta LI dynamics may provide a preliminary candidate electrophysiological feature for characterizing post-stroke emotional dysfunction.
Key Findings
Results
Stroke patients showed reduced valence and arousal responses to positive emotional clips, with this reduction being particularly pronounced in right-hemisphere stroke patients.
15 patients with left-hemisphere stroke (L-stroke), 15 patients with right-hemisphere stroke (R-stroke), and 15 healthy controls were studied
Self-Assessment Manikin ratings were collected after each film clip to assess valence and arousal
Positive, neutral, and negative validated film clips were used as stimuli during 64-channel EEG recording
The reduction in emotional response to positive clips was especially notable in R-stroke patients compared to L-stroke and healthy controls
Results
Low-frequency spectral power analysis showed preserved emotion modulation across groups, meaning basic emotional differentiation in spectral power was not eliminated by unilateral stroke.
Spectral power was computed across participants in all three groups
Emotion modulation in spectral power was preserved despite unilateral stroke lesions in both hemispheres
This finding contrasts with the disruptions observed in dynamic lateralization measures
Emotion-averaged lateralization index (LI) mainly reflected group-dependent hemispheric bias rather than dynamic emotional processing differences
Results
Left-hemisphere stroke was associated with higher lateralization detectability and lower switching rate during positive clip processing, indicating a more stable but less flexible pattern of hemispheric lateralization.
Within-clip parietal-theta LI dynamics were assessed using detectability, switching rate, and entropy measures
L-stroke patients showed higher detectability compared to R-stroke and controls during positive clips
L-stroke patients showed lower switching rate during positive emotional processing
These measures captured dynamic temporal organization of emotional brain states not visible in time-averaged lateralization
Results
Right-hemisphere stroke was associated with increased switching rate and entropy during positive clip processing, indicating greater instability and less predictable hemispheric lateralization dynamics.
R-stroke patients showed increased switching rate during positive clips compared to L-stroke and healthy controls
R-stroke patients showed increased entropy of parietal-theta LI during positive emotional processing
Increased switching and entropy reflect a less stable, more variable pattern of hemispheric lateralization
These differences were specific to the parietal-theta frequency band and positive emotional content
Results
Switching rate showed a group-dependent association with arousal, with stronger coupling between switching and arousal observed in right-hemisphere stroke patients.
Mixed-effects models were used to account for repeated observations within participants and variability across film clips
The association between switching rate and arousal was group-dependent in the primary model
R-stroke patients exhibited stronger coupling between LI switching and arousal ratings compared to other groups
This suggests that the relationship between brain state dynamics and subjective emotional experience is altered differently depending on lesion hemisphere
Results
Inter-clip LI stability was computed and, along with emotion-averaged LI, captured group-dependent hemispheric bias but did not reveal the hemisphere-specific dynamic differences found in within-clip measures.
Both emotion-averaged LI and inter-clip LI stability were computed as part of the analysis framework
These time-averaged or stability measures primarily reflected group-dependent hemispheric bias
The hemisphere-group-associated differences in stability-flexibility balance were not captured by these time-averaged measures
Within-clip dynamic measures (detectability, switching rate, entropy) were necessary to reveal the differential effects of left vs. right hemisphere lesions
Conclusions
Parietal-theta LI dynamics were identified as a preliminary candidate electrophysiological feature for characterizing post-stroke emotional dysfunction.
The study used a cross-sectional design with three groups of 15 participants each (total N=45)
64-channel EEG was recorded during naturalistic emotional processing using film clips
Dynamic hemispheric lateralization in the parietal-theta band captured hemisphere-group-associated differences beyond conventional spectral or time-averaged measures
The authors describe these findings as 'preliminary' given the sample size and cross-sectional design
What This Means
This research suggests that when a stroke occurs on one side of the brain, it disrupts the way the two hemispheres of the brain take turns being active during emotional experiences — and it does so differently depending on which side is damaged. The researchers recorded brain activity (EEG) from 45 people (15 with left-hemisphere stroke, 15 with right-hemisphere stroke, and 15 healthy controls) while they watched emotional film clips. They found that people with right-hemisphere strokes had notably reduced emotional responses to positive content, and their brain activity showed rapid, unpredictable switching between hemispheres. By contrast, people with left-hemisphere strokes showed more stable but inflexible hemispheric activity patterns during emotional processing.
This research suggests that traditional ways of measuring brain activity — which average signals over time — miss important information about how the brain dynamically shifts between its two sides during emotional experiences. When the researchers used new measures that tracked these shifts moment-to-moment within each film clip (called switching rate, detectability, and entropy of lateralization), they uncovered clear differences between left- and right-stroke patients that the simpler averages could not detect. The parietal region of the brain in the theta frequency range was particularly informative for distinguishing these patterns.
This research suggests that the way the brain's two hemispheres coordinate during emotional processing is disrupted after stroke in hemisphere-specific ways, with right-hemisphere damage causing more instability and left-hemisphere damage causing more rigidity. These dynamic EEG measures of hemispheric balance could potentially serve as biomarkers to better understand and characterize emotional difficulties that commonly occur after stroke, though the study's small sample size and cross-sectional design mean further research is needed before clinical applications could be considered.
Han M, Tang Y, Lv Y, Chen X, Liu X, Chen Z, et al.. (2026). Dynamic Hemispheric Lateralization of Naturalistic Emotional Processing After Unilateral Stroke: An EEG Study.. CNS neuroscience & therapeutics. https://doi.org/10.1002/cns.71096