No abstract

Our understanding of post-stroke language function is largely based on older age groups, who show increasing age-related brain pathology and neural reorganisation. To illustrate language outcomes in the young-adult brain, we present the case of A., a 23 y.o. woman with chronic aphasia from a left-hemisphere stroke affecting the temporal lobe. Diffusion MRI-based tractography indicated that A.'s language-relevant white matter structures were severely damaged. Using magnetoencephalography (MEG), we explored A.'s conceptual preparation and word planning abilities. Context-driven and bare picture-naming tasks revealed naming deficits, manifesting as word-finding difficulties and semantic paraphasias about half of the time. Naming was however facilitated by semantically constraining lead-in sentences. Altogether, this pattern indicates relatively spared conceptual preparation but disrupted lexical and phonological retrieval abilities. MEG revealed that A.'s conceptual and naming-related neural responses were supported by the right hemisphere, compared to the typical left-lateralised brain response of a matched control. Differential recruitment of right-hemisphere structures (330-440 ms postpicture onset) was found concurrently during successful naming (right mid-to-posterior temporal lobe) and word-finding attempts (right inferior frontal gyrus). Disconnection of the temporal lobes via corpus callosum was not critical for recruitment of the right hemisphere in visuallyguided naming, possibly due to neural activity right-lateralising from the outset. We consider that, despite A.'s young age, the presumed strong degree of language lateralisation and extensive structural damage limited her recovery. Although A.'s right hemisphere responded in a timely manner during word planning, its lexical and phonological retrieval abilities remained modest.

Studies have shown that older adults with high Cognitive Reserve (HCR) exhibit better executive functioning than their low CR (LCR) counterparts. However, the neural processes linked to those differences are unclear. This study investigates (1) the neural processes underlying enhanced executive functions in older adults with HCR and (2) how executive control differences are modulated by task difficulty. We recruited 74 participants, who performed two executive control tasks with different difficulty levels while recording the electroencephalogram. The accuracy on both tasks requiring inhibition of irrelevant information was better in the HCR than the LCR group. Also, in the more demanding task, event-related potentials (ERP) latencies related to inhibition and working memory update were faster in HCR than LCR. Moreover, the HCR, but not the LCR, showed larger P300 amplitude in parietal than frontal regions and in the left than right hemisphere, suggesting a posterior to anterior shift of activity and loss of inter-hemispheric asymmetries in LCR participants. These results suggest that high CR counteracts neural activity changes related to ageing. Thus, high levels of CR can be related to maintenance of neural activity patterns typically observed in young adults rather than to deployment of neural compensatory mechanisms.

Our understanding of post-stroke language recovery and underlying neuroplasticity is largely based on older age groups, who have increasing brain pathology and potentially more bilateral language functioning. We present the case of A., a 23 y.o. woman with chronic aphasia from a left-hemisphere stroke. Deterministic tractography indicated that A.’s language-relevant white matter structures were severely damaged. Using magnetoencephalography (MEG), we explored A.’s conceptual preparation and subsequent word planning abilities. Context-driven and Bare picture-naming tasks revealed substantial naming deficits, manifesting as word-finding difficulties and semantic paraphasias about half of the time. Naming was however facilitated by semantically constraining lead-in sentences. Altogether, this pattern indicates intact conceptual preparation but disrupted lexical and phonological retrieval abilities. MEG revealed that A.’s naming-related neural responses differed from that of a matched control. Source localisation showed active but differential recruitment of right-hemisphere structures (300-400 ms post-picture onset) during both correct naming (right temporo-parietal regions) and anomic (right inferior frontal gyrus) attempts. We consider that, despite A.’s young age, the presumed strong degree of language lateralisation and extensive structural damage limited her recovery. Although A.’s right hemisphere responded in a timely manner during word planning, its lexical and phonological retrieval abilities remained modest.