The volume and the distribution of premorbid white matter hyperintensities: Impact on post-stroke aphasia.

White matter hyperintensities (WMH) are a radiological manifestation of progressive white matter integrity loss. The total volume and distribution of WMH within the corpus callosum have been associated with pathological cognitive ageing processes but have not been considered in relation to post-stroke aphasia outcomes. We investigated the contribution of both the total volume of WMH, and the extent of WMH lesion load in the corpus callosum to the recovery of language after first-ever stroke. Behavioural and neuroimaging data from individuals (N = 37) with a left-hemisphere stroke were included at the early subacute stage of recovery. Spoken language comprehension and production abilities were assessed using word and sentence-level tasks. Neuroimaging data was used to derive stroke lesion variables (volume and lesion load to language critical regions) and WMH variables (WMH volume and lesion load to three callosal segments). WMH volume did not predict variance in language measures, when considered together with stroke lesion and demographic variables. However, WMH lesion load in the forceps minor segment of the corpus callosum explained variance in early subacute comprehension abilities (t = -2.59, p = .01) together with corrected stroke lesion volume and socio-demographic variables. Premorbid WMH lesions in the forceps minor were negatively associated with early subacute language comprehension after aphasic stroke. This negative impact of callosal WMH on language is consistent with converging evidence from pathological ageing suggesting that callosal WMH disrupt the neural networks supporting a range of cognitive functions.

Online transcranial magnetic stimulation reveals differential effects of transitivity in left inferior parietal cortex but not premotor cortex during action naming.

Accumulating evidence indicates two cortical regions, the left ventral premotor cortex (PMv) and left intraparietal sulcus (IPS), are involved in spoken verb production. Some evidence also indicates these regions may be differentially engaged by transitive (i.e., object-oriented) versus intransitive actions. We explored the role of these regions during action picture naming in two experiments, each employing high frequency (10 Hz) online repetitive Transcranial Magnetic Stimulation (rTMS) in 20 participants. In Experiment 1, participants named intransitive action pictures (e.g., LAUGH) accompanied by active and sham rTMS to the left PMv, left IPS, and right superior parietal lobule (SPL; control site). Application of rTMS to PMv resulted in slower naming latencies compared to sham and control site stimulation, whereas stimulation of the IPS did not result in any significant effects. Experiment 2 employed active and sham rTMS identical to Experiment 1 with transitive action pictures (e.g., PUSH). Stimulation of both regions induced changes in naming latencies compared to sham and control site stimulation, with rTMS applied to PMv slowing responses and IPS stimulation facilitating them. Surprisingly, stimulation of the right SPL control site also slowed naming compared to sham across both Experiments. Overall, these findings indicate different roles for PMv and IPS during action picture naming. Specifically, the divergent effects of PMv and IPS stimulation in the transitive action naming task indicate different processes likely operate in the two regions during verb production. Involvement of the right SPL across both transitive and intransitive action naming might reflect visuospatial or general attention mechanisms rather than language processes per se.