The Concise Language Paradigm in left and right hemisphere stroke: a longitudinal source-localized EEG study

Language recovery after stroke can be supported by neuroplasticity, but its underlying mechanisms remain poorly understood. Most previous studies have either focused on language comprehension or production and/or relied on hemodynamic measures, with limited complementary electrophysiological evidence. Here, we combined a paradigm assessing comprehension and production with individualized electroencephalography (EEG) source reconstruction to investigate post-stroke language function and changes in hemispheric dominance over time.

We tested 31 participants: 13 stroke-free controls, 8 individuals with left hemisphere (LH), and 10 with right hemisphere (RH) stroke in the middle cerebral artery territory. Participants with stroke were assessed approximately two and seven months post-stroke. We employed the Concise Language Paradigm (CLaP), which combines auditory sentence comprehension with picture naming, in addition to standardized neuropsychological tests. EEG data were analyzed using event-related potentials and time-frequency representations, followed by source reconstruction based on individual MRI-derived forward models. Laterality indices were calculated to assess changes in hemispheric dominance between sessions.

Behaviorally, the LH group showed low performance at two months followed by overall improvement, whereas the RH group mainly improved in visuospatial memory and functional communication. EEG activity was significantly modulated by task condition across comprehension and production contrasts. Source-level results in controls were consistent with established language-related networks, serving as regions of interest for the stroke analyses. In the stroke groups, hemispheric dominance differed between LH and RH stroke participants. Notably, several LH participants shifted from left-to right-hemisphere dominance between sessions, whereas those initially showing right-hemisphere dominance remained stable.

Our study provides evidence on comprehension and production performance after stroke using a single paradigm. These findings demonstrate dynamic changes in hemispheric dominance during post-stroke recovery, ultimately highlighting the value of individualized EEG source reconstruction to investigate post-stroke plasticity.