Different patterns of language activation in post-stroke aphasia are detected by overt and covert versions of the verb generation fMRI task

Abstract

Summary Background Post-stroke language functions depend on the relative contributions of the dominant and non-dominant hemispheres. Thus, we aimed to identify the neural correlates of overt and covert verb generation in adult post-stroke aphasia. Material/Methods Sixteen aphasic LMCA stroke patients (SPs) and 32 healthy controls (HCs) underwent language testing followed by fMRI while performing an overt event-related verb generation task (ER-VGT) isolating activations related to noun-verb semantic processing or to articulation and auditory processing, and a covert block design verb generation task (BD-VGT). Results BD-VGT activation patterns were consistent with previous studies, while ER-VGT showed different patterns in SPs relative to HCs including less left-hemispheric involvement during semantic processing and predominantly right-sided activation related to articulation and auditory processing. ER-VGT intra-scanner performance was positively associated with activation during semantic associations in the left middle temporal gyrus for HCs (p=0.031) and left middle frontal gyrus for SPs (p=0.042). Increased activation in superior frontal/cingulate gyri was associated with better intra-scanner performance (p=0.020). Lesion size negatively impacted verbal fluency tested with Controlled Oral Word Association Test (p=0.0092) and the Semantic Fluency Test (p=0.033) and trended towards a negative association with verb generation performance on the event-related verb generation task (p=0.081). Conclusions Greater retention of pre-stroke language skills is associated with greater involvement of the left hemisphere with different cortical recruitment patterns observed in SPs versus HCs. Post-stroke verbal fluency may depend more upon the structural and functional integrity of the dominant left hemisphere language network rather than the shift to contralateral homologues.

Recovering two languages with the right hemisphere

“…1). This suggests that in this patient the reorganization of the neural network that subserves the process of lexical selection has recruited an epicenter (the right middle temporal gyrus) which mirrors the activation in the left middle temporal gyrus observed in the group of healthy participants in the study by Allendorfer et al (2012).…”

“…This finding is particularly interesting. In healthy individuals, this task usually elicits activations in left frontotemporo-parietal areas as well as in the right cerebellum (Allendorfer, Kissela, Holland, & Szaflarski, 2012;Fiez, Raichle, Balota, Tallal, & Petersen, 1996;Szaflarski et al, 2006). For example, in a group of 32 healthy adult participants, Allendorfer et al (2012) reported activations in an articulated neural network which comprised areas in the LH (left middle frontal gyrus, left middle temporal gyrus, left inferior parietal lobule), RH (right superior temporal gyrus) and in both hemispheres (bilateral insula and superior temporal, inferior frontal and cingulate gyri) as well as the right cerebellar hemisphere.…”

“…In healthy individuals, this task usually elicits activations in left frontotemporo-parietal areas as well as in the right cerebellum (Allendorfer, Kissela, Holland, & Szaflarski, 2012;Fiez, Raichle, Balota, Tallal, & Petersen, 1996;Szaflarski et al, 2006). For example, in a group of 32 healthy adult participants, Allendorfer et al (2012) reported activations in an articulated neural network which comprised areas in the LH (left middle frontal gyrus, left middle temporal gyrus, left inferior parietal lobule), RH (right superior temporal gyrus) and in both hemispheres (bilateral insula and superior temporal, inferior frontal and cingulate gyri) as well as the right cerebellar hemisphere. In the same study, 16 chronic aphasic participants with lesions in the LH showed a partially different pattern of activations in the LH (left parahippocampal, middle and superior temporal gyri, and left middle frontal gyrus), RH (right middle and superior temporal gyri), bilaterally (bilateral superior and inferior frontal gyri) with the involvement of the basal ganglia (left caudate).…”

Surgical Aspects of Decompression Craniectomy in Malignant Stroke: Review

“…A growing body of evidence originating from transcranial magnet stimulation studies (TMS) shows functional reorganization of language in aphasic patients [72]. While it is broadly assumed that shifting of functional language regions to the nondominant hemisphere might establish the foundation for recovery, current fMRI studies, however, demonstrate that patients with normal or close-to-normal language functions at least 1 year after stroke show a return to typical fMRI activation patterns when compared to the results of fMRI data obtained in previous studies that included healthy controls and comparable language tasks [73,74]. Reorganization of language functions by shifting to the right hemispheric brain regions was shown to be a less effective mode of language function recovery [73,74,75].…”

“…Though it might be problematic to indicate decompression craniectomy in older patients considering aphasia, involvement of the dominant hemisphere does not pose a contraindication for younger patients and should be performed as early as possible [67,74]. Nevertheless, in two-thirds of involved patients, aphasia remained unchanged 12 months later and neuropsychological testing has revealed that 62% of the aphasic patients fulfilled the DSM-III-R criteria for depression 12 months after stroke.…”