Subcortical Aphasia

Abstract

Background and Purpose-Very few neuroimaging studies have focused on follow-up of subcortical aphasia. Here, overt language production tasks were used to correlate regional cerebral blood flow (rCBF) changes and language performance in patients with vascular subcortical lesions. Methods-Seven aphasic patients were scanned twice with positron emission tomography (PET) at 1-year interval during a word-generation task. Using SPM2, Language-Rest contrast at PET1 was correlated to language performance and to time-lag from stroke. The same contrast was performed at PET2 and session effect (PET2-PET1) was correlated with performance improvement. Results-At PET1, correlation between rCBF and delay from stroke involved mainly ventral regions of the left temporal cortex and mesial frontal cortex. Correlations between rCBF and performance showed predominantly left dorsal regions in the frontal, temporal, and parietal lobes, but also the left ventral temporal cortex. One year apart, language performance improved and rCBF increased in perisylvian regions bilaterally. Best performers at PET2 showed an increase of activity in left ventral temporal cortex as well as in right middle temporal gyrus. Conclusions-On follow-up, expected language improvement and increase of activation in the classical language areas and their counterparts were observed. Moreover, all correlational analyses both at PET1 and on follow-up implicated the anterior part of the left inferior temporal gyrus, suggesting a disconnection between the superior and inferior parts of the left temporal cortex and a specific role for this region in lexical semantic processing.

Language recovery and evidence of residual deficits after nonthalamic subcortical stroke: A 1 year follow-up study

“…Although the BG are bilaterally involved in word generation, the left pre-SMA-BG ventral anterior thalamic loop has a role in word retrieval from lexical stores whereas the right BG have an inhibitory effect on the right frontal regions to prevent interference on language production (Crosson et al, 2003). Importantly, verbal fluency deficits were the most common impairment observed at 1 year, which supports the initial findings of de Boissezon et al (2005) revealing that executive language recovery as measured by a word generation task was not fully completed at 1 year post stroke.…”

“…Semantic fluency tests are sensitive to frontal lobe dysfunction after either left or right cortical injury (Baldo & Shimamura, 1998). Yet, impaired performance in tests measuring verbal fluency and word generation has also been reported in patients with BG stroke (de Boissezon et al, 2005;Kuljic-Obradovic, 2003;Mega & Alexander, 1994;Radanovic et al, 2004).…”

Neurophysiological Markers of Language Recovery in Subacute Stroke

“…Longitudinal neuroimaging studies on groups of patients have also been carried out to determine the neural mechanisms that are involved at different stages of the recovery process both in cortical (Heiss et al, 1999) and subcortical structures (de Boissezon et al, 2005). The study by Heiss et al (1999) demonstrated initial right hemisphere recruitment at two weeks post-stroke with a shift to perilesional regions at eight weeks.…”

“…Perilesional activity has been associated with a good recovery (Heiss et al, 1999) as has bilateral activation (Cardebat et al, 2003;de Boissezon et al, 2005). The benefits of other mechanisms such as right hemisphere homologues are less clear.…”

“…In another longitudinal PET study, Cardebat et al (2003) recruited aphasic patients at 2 and 11 months post-stroke and demonstrated that increased activation in perisylvian regions was associated with improved language outcome. de Boissezon et al (2005) employed the same experimental paradigm as that of Cardebat et al (2003) in a subgroup of patients with subcortical aphasia and showed that language improvement was associated with increased activity in bilateral temporal regions. However the process of reorganisation, in terms of the timing and extent to which different neural mechanisms are recruited over the course of recovery, was not considered in either of these studies.…”