Mechanisms of and misconceptions about subcortical aphasia

Which is responsible for aphasia by subcortical lesions? Subcortical lesions or the cortical hypoperfusion?

Cerebral lesions causing aphasia involve morphological and functional changes. In this study, it was aimed to explain the connection between aphasia and subcortical lesions with SPECT. The study included 30 patients diagnosed in the first three days of stroke with a single hemorrhagic or ischemic lesion in the dominant hemisphere subcortical area. Gulhane Aphasia Test and SPECT were performed. Aphasia was detected in 19 cases (63.3%). The relationship between aphasia and perfusion dysfunction in cortical and subcortical regions of the brain was evaluated, aphasia was found to be present in 15 (71.4%) of the 21 patients with cortical hypoperfusion in the dominant hemisphere and 4 (44.4%) of the 9 patients without cortical hypoperfusion; the difference was not statistically significant (p = 0.16). In the ischemia group, aphasia was present in 11 (78.5%) of the 14 cases with cortical hypoperfusion in the dominant hemisphere. Aphasia wasn't detected in any of the 5 cases that did not have cortical hypoperfusion, the difference was statistically significant (p = 0.005). When cerebral regions were evaluated separately, significant difference was reported in the aphasia seen with frontal, anterior parietal, and occipital hypoperfusion compared to cases with normal perfusion in these areas, with p = 0.003, p = 0.021, and p = 0.004, respectively. This study showed that aphasia to be more common in cases with cortical hypoperfusion in the dominant hemisphere than in cases without hypoperfusion. Our results provide evidence that direct effect of the lesion in the basal ganglia on the development of aphasia is doubtful.

Remote cortical atrophy and language outcomes after chronic left subcortical stroke with aphasia

Objective

Subcortical stroke can cause a variety of language deficits. However, the neural mechanisms underlying subcortical aphasia after stroke remain incompletely elucidated. We aimed to determine the effects of distant cortical structures on aphasia outcomes and examine the correlation of cortical thickness measures with connecting tracts integrity after chronic left subcortical stroke.

Methods

Thirty-two patients and 30 healthy control subjects underwent MRI scanning and language assessment with the Western Aphasia Battery-Revised (WAB-R) subtests. Among patients, the cortical thickness in brain regions that related to language performance were assessed by the FreeSurfer software. Fiber tracts connecting the identified cortical regions to stroke lesions were reconstructed to determine its correlations with the cortical thickness measures across individual patient.

Results

Cortical thickness in different parts of the left fronto-temporo-parietal (FTP) regions were positively related to auditory-verbal comprehension, spontaneous speech and naming/word finding abilities when controlling for key demographic variables and lesion size. Cortical thickness decline in the identified cortical regions was positively correlated with integrity loss of fiber tracts connected to stroke lesions. Additionally, no significant difference in cortical thickness was found across the left hemisphere between the subgroup of patients with hypoperfusion (HP) and those without HP at stroke onset.

Conclusions

These findings suggest that remote cortical atrophy independently predicts language outcomes in patients with chronic left subcortical stroke and aphasia and that cortical thinning in these regions might relate to integrity loss of fiber tracts connected to stroke lesions.

Resolution of diaschisis contributes to early recovery from post-stroke aphasia

Diaschisis is a phenomenon observed in stroke that is defined as neuronal dysfunction in regions spared by the infarction but connected to the lesion site. We combined lesion network mapping and task-based functional MRI in 71 patients with post-stroke aphasia to investigate, whether diaschisis and its resolution contribute to early loss and recovery of language functions. Language activation acquired in the acute, subacute and chronic phase was analyzed in compartments with high and low normative resting-state functional connectivity to the lesion site on an individual basis. Regions with high compared to regions with low lesion connectivity showed a steeper increase in language reactivation from the acute to the subacute phase. This finding is compatible with the assumption of resolution of diaschisis. Additionally, language performance in the subacute phase and improvement from the subacute to the chronic phase significantly correlated with the diaschisis effect and its resolution, respectively, suggesting a behavioral relevance of this effect. We therefore assume that undamaged but functionally connected regions become dysfunctional due to missing input from the lesion contributing to the aphasic deficit. Since these regions are structurally intact, dysfunction resolves over time contributing to the rapid early behavioral improvement observed in aphasic stroke patients. Our results demonstrate that diaschisis and its resolution might be a relevant mechanism of early loss and recovery of language function in acute stroke patients.

Subcortical neglect is not always a transient phenomenon: evidence from a 1-year follow-up study

Compared to cortical lesions, spatial neglect following subcortical stroke is most frequently seen as a mild and transient phenomenon. Since this assumption is based on only few observations, we reexamined the prognosis and severity of spatial neglect in patients with circumscribed right-sided basal ganglia or thalamic lesions in the acute and in the chronic phase of the stroke. On average, 1.15 years after stroke, spatial neglect had persisted in about 40% of the patients with subcortical lesions. The severity was reduced to about one third. The results argue against the view that spatial neglect following subcortical lesions typically has a favorable prognosis.

'Anatomo-biological considerations on the centers of language': an Argentinian contribution to the 1906 Paris debate on aphasia

In 1906, the year of the renowned holistic-localizationist controversy between neurologists Pierre Marie and Jules Déjèrine in Paris, Christfried Jakob, a protagonist researcher of the cerebral cortex at the time working in Argentina, published two relevant articles entitled 'Does Broca's area exist?' and 'Anatomo-biological considerations on the centers of language'. The two articles addressed neuropsychological and developmental aspects of language functions in normality and pathology with regard to the brain areas that subserve them. The present article provides an English translation of Jakob's second paper, on the embryonic and postnatal development of brain areas related to language. The information given and the views expressed may still shed, a century later, useful light on our understanding of brain-language relationships.

Pharmacological, surgical, and neurovascular interventions to augment acute aphasia recovery

Aphasia recovery has often been attributed to a combination of "spontaneous recovery" and rehabilitation. However, a variety of new pharmacological, surgical, and interventional neuroradiology procedures have been developed that can complement rehabilitation in the first days to weeks after stroke by restoring blood flow to dysfunctional but salvageable brain tissue. This paper will review the medical and surgical interventions to improve regional cerebral blood flow that recently have been shown to (1) augment aphasia recovery by improving tissue function, and (2) prevent expansion of the stroke that would otherwise impede recovery. Success with such treatments facilitates aphasia rehabilitation by improving the baseline language performance that must be improved further with language therapy.

Cortical abnormalities and language function in young patients with basal ganglia stroke

We examined MRI abnormalities and language function in young patients with infarctions apparently confined to the basal ganglia to establish whether impaired performance was attributable to basal ganglia damage per se or to additional cerebral abnormalities. Seventeen stroke patients (10 with left- and 7 with right-hemispheric damage) and seventeen controls participated. MRI included perfusion imaging and voxel-based morphometry analyses of T1-weighted and diffusion data sets. Language was assessed using the CELF-III test. Analysis of CELF-III scores showed a main effect of presence or absence of stroke, with patients performing more poorly than controls. There was no evidence of differences between the left- and right-hemisphere groups. However individual patients with left-hemisphere lesions showed large variations in performance. In the patients with left-hemisphere damage, voxel-based morphometry showed significant relationships between language function and gray matter density in cortical language areas. The white matter analyses also showed correlations with language function, and in addition there were hemodynamic abnormalities in cortical language areas in the three patients with poorest language function. We suggest that language impairments following basal ganglia damage may be attributable primarily to abnormalities in cortical language areas that are too subtle to detect on conventional structural MRI.

Atypical language representation in epilepsy: implications for injury-induced reorganization of brain function

This review addresses language function and reorganization associated with various forms of epilepsy. Longstanding epilepsy, particularly types with onset early in life, may be associated with changes in the representation of language function in the brain. As a result of this reorganization, language function may be relatively spared despite injury to areas of the brain that normally subserve these functions. We examine the changes seen in language function in two types of epilepsy: hemispheric epilepsy of childhood and focal epilepsies. Findings from behavioral studies, intracarotid amytal testing, intraoperative cortical testing, and more recent functional imaging studies are reviewed. Studying changes in the representation of language function seen in some forms of epilepsy provides information about brain plasticity with implications for other neurologic diseases, as well as for the neuroscientific understanding of how and when functional reorganization may occur.

Subcortical aphasia: three different language disorder syndromes?

The study analyses clinical presentation of language functions of 32 patients with subcortical aphasia induced by stroke. The patients have been divided into three groups according to neuroanatomic localization of the lesion, defined by CT and MRI examination (striato-capsular aphasia, aphasia associated with white matter paraventricular lesions and thalamic aphasia). The following batteries and tests were used: the neurologic examination, CT scan, MRI, Doppler ultrasound, Mini Mental State Examination, Boston Diagnostic Aphasia Examination (BDAE), Boston Naming Test (BNT), Token Test and Verbal Fluency Test. Clinical presentation of subcortical aphasias is characterized with preserved repetition, however, some groups differ by certain specific features of language impairment. Striato-capsular aphasia and aphasia associated with white matter paraventricular lesions are characterized with lack of speech fluency, occurrence of literary paraphasias, mainly preserved comprehension and naming. Thalamic aphasia, however, is characterized with fluent output, impaired comprehension and naming with predominant verbal paraphasias. The specific features of language impairment suggest that subcortical structures contribute to language organization. Considering the results of language tests we presume that the most prominent feature in striato-capsular aphasia is phonetic impairment of language, opposite to thalamic aphasia where lexical-sematic processing seems to be affected.

[Clinical characteristics of speech-language dysfunctions in thalamic aphasia]

The aim of this study was to investigate the characteristic symptom cluster and the course of aphasia in 12 patients with single left thalamic lesion verified by CAT scan. The testing of language disorder was performed by standard linguistic tests for aphasia in the acute stage and one month after the insult. Although this clinical syndrome varied greatly it was possible to point out some common characteristics. Spontaneous speech was fluent, easily articulated, grammatically correct, with preserved melodic line. Word finding and understanding were impaired. The impaired comprehension and naming were prominent in all patients with different severity. Repetition skills were intact. During the naming testing patients accomplished better results after semantic help than after phonetic help. Verbal paraphasia errors appeared more frequently (9.78) than neologistic (2.22) and literal paraphasias (1.78). Results of the language fluency tests were worse during semantic categorization tests (5.50) than during animal naming (9.89). On the basis of these facts it was presumed that aphasia in patients with dominant thalamic lesion was the result of lexicosemantic language disorder. It was statistically proved that recovery from aphasia in these cases tended to be significant and rapid.

Subcortical aphasia and neglect in acute stroke: the role of cortical hypoperfusion

We have hypothesized that most cases of aphasia or hemispatial neglect due to acute, subcortical infarct can be accounted for by concurrent cortical hypoperfusion. To test this hypothesis, we demonstrate: (i) that pure subcortical infarctions are associated with cortical hypoperfusion in subjects with aphasia/neglect; (ii) that reversal of cortical hypoperfusion is associated with resolution of the aphasia; and (iii) that aphasia/neglect strongly predicts cortical ischaemia and/or hypoperfusion. We prospectively evaluated a consecutive series of 115 patients who presented within 24 h of onset or progression of stroke symptoms, with MRI sequences including diffusion weighted imaging (DWI) and perfusion weighted imaging (PWI), and detailed testing for aphasia or hemispatial neglect. The association between aphasia or neglect and cortical infarct (or dense ischaemia) on DWI and cortical hypoperfusion indicated by PWI, was evaluated with chi-squared analyses. Fisher exact tests were used for analyses with small samples. Cases of DWI lesion restricted to subcortical white matter and/or grey matter structures (n = 44) were examined for the presence of aphasia or neglect, and for the presence of cortical hypoperfusion. In addition, subjects who received intervention to restore perfusion were evaluated with DWI, PWI, and cognitive tests before and after intervention. Finally, the positive predictive value of the cognitive deficits for identifying cortical abnormalities on DWI and PWI were calculated from all patients. Of the subjects with only subcortical lesions on DWI in this study (n = 44), all those who had aphasia or neglect showed concurrent cortical hypoperfusion. Among the patients who received intervention that successfully restored cortical perfusion, 100% (six out of six) showed immediate resolution of aphasia. In the 115 patients, aphasia and neglect were much more strongly associated with cortical hypoperfusion (chi(2) = 57.3 for aphasia; chi(2) = 28.7 for neglect; d.f. = 1; P < 0.000001 for each), than with cortical infarct/ischaemia on DWI (chi(2) = 8.5 for aphasia; chi(2) = 9.7 for neglect; d.f. = 1; P < 0.005 for each). Aphasia showed a much higher positive predictive value for cortical abnormality on PWI (95%) than on DWI (62%), as did neglect (100% positive predictive value for PWI versus 74% for DWI). From these data we conclude that aphasia and neglect due to acute subcortical stroke can be largely explained by cortical hypoperfusion.

Language organization in patients with early and late left-hemisphere lesion: a PET study

Functional neuroimaging studies have shown enhanced right-hemisphere language activations in adults with left-hemisphere damage. We hypothesized that this effect would be stronger in patients with lesion occurring early in development. Using [15O]-water PET, we studied eight normal adults and 23 patients with unilateral left lesion during rest, listening to sentences, and sentence repetition. Thirteen patients had lesions with early onset (< 5 years) and ten had lesions with late onset (> 20 years). For listening to sentences, frontotemporal blood flow increases were significantly stronger in the left than in the right hemisphere in normal adults. This normal asymmetry was reduced in patients with late lesion and reversed in those with early lesion. For sentence repetition, analogous group differences were significant for the basal ganglia, but failed to reach significance for the (pre)motor and insular regions. We conclude that left lesion leads to alterations in the asymmetry of language activations (in and beyond the perisylvian areas). In addition, rightward shifts of language activation tend to be stronger as a consequence of early (as compared to late) lesion. Finally, postlesional reorganization appears to reflect a coexistence of 'additive' and 'subtractive' effects, i.e., activation in some regions that are not normally involved in language processing and lack of activation in other (undamaged) regions that are normally activated by language tasks.