Advanced Magnetic Resonance Neuroimaging of Language Function Recovery After Aphasic Stroke: A Technical Review

Mechanisms of brain activation following naming therapy in aphasia: A systematic review on task-based fMRI studies

The pattern of brain neuroplasticity after naming therapies in patients with aphasia can be evaluated using task-based fMRI. This article aims to review studies investigating brain reorganization after semantic and phonological-based anomia therapy that used picture-naming fMRI tasks. We searched for those articles that compared the activation of brain areas before and after aphasia therapies in the PubMed and the EMBASE databases from 1993 up to April 2020. All studies (single-cases or group designs) on anomia treatment in individuals with acquired aphasia were reviewed. Data were synthesized descriptively through tables to allow the facilitated comparison of the studies. A total of 14 studies were selected and reviewed. The results of the reviewed studies demonstrated that the naming improvement is associated with changes in the activation of cortical and subcortical brain areas. This review highlights the need for a more systematic investigation of the association between decreased and increased activation of brain areas related to anomia therapy. Also, more detailed information about factors influencing brain reorganization is required to elucidate the neural mechanisms of anomia therapy. Overall, regarding the theoretical and clinical aspects, the number of studies that used intensive protocol is growing, and based on the positive potential of these treatments, they could be suitable for the rehabilitation of people with aphasia.

Altered Spontaneous Brain Activity in Poststroke Aphasia: A Resting-State fMRI Study

PURPOSE

Brain areas frequently implicated in language recovery after stroke comprise perilesional sites in the left hemisphere and homotopic regions in the right hemisphere. However, the neuronal mechanisms underlying language restoration are still largely unclear.

METHODS AND MATERIALS

In the present study, we investigated the brain function in 15 patients with poststroke aphasia and 30 matched control subjects by combining the regional homogeneity (ReHo) and amplitudes of low-frequency fluctuation (ALFF) analysis methods based on resting-state fMRI.

RESULTS

Compared to the control subjects, the patients with aphasia exhibited increased ReHo and ALFF values in the ipsilateral perilesional areas and increased ReHo in the contralesional right middle frontal gyrus.

CONCLUSIONS

The increased spontaneous brain activity in patients with poststroke aphasia during the recovery period, specifically in the ipsilateral perilesional regions and the homologous language regions of the right hemisphere, has potential implications for the treatment of patients with aphasia.

Does acupuncture therapy improve language function of patients with aphasia following ischemic stroke? A systematic review and meta-analysis

BACKGROUND

Aphasia is one of the most common complications in patients with ischemic stroke. Studies have shown that acupuncture can improve the symptoms of aphasia patients. However, the effect of acupuncture on language function in patients with ischemic stroke is still controversial.

OBJECTIVE

This study aimed to critically assess the efficacy and safety of acupuncture for aphasia following ischemic stroke.

METHODS

PubMed, Embase, Cochrane Central Register of Controlled Trials, Web of Science Core Collection, China National Knowledge Infrastructure, Wanfang Digital Periodicals, and Chinese Science and Technology Periodicals database were searched. All randomized controlled trials (RCTs) that met the criteria were included.

RESULTS

Meta-analyses showed that mean difference in change of auditory comprehension score (MD = 7.71, 95% CI: 1.83 to 13.59, P = 0.01), spontaneous speech (MD = 2.77, 95% CI: 0.59 to 4.95, P = 0.01), repetition score (MD = 14.48, 95% CI: 11.04 to 17.91, P <  0.00001) and naming score (MD = 14.60, 95% CI: 11.33 to 17.88, P <  0.00001) measured by WAB scale were statistically significant. Subgroup analyses demonstrated that there were statistically significant mean differences in four items of WAB scale in patients with sub-acute stroke, and no statistically significant differences in patients with acute stroke.

CONCLUSION

The present study suggests that acupuncture may improve the language function of patients with aphasia following ischemic stroke, especially during the sub-acute phase. However, due to insufficient sample sizes and information on the safety, more high-quality RCTs are still needed.

Diffusion tensor imaging point to ongoing functional impairment in HIV-infected children at age 5, undetectable using standard neurodevelopmental assessments

Background

Perinatal HIV infection negatively impacts cognitive functioning of children, main domains affected are working memory, processing speed and executive function. Early ART, even when interrupted, improves neurodevelopmental outcomes. Diffusion tension imaging (DTI) is a sensitive tool assessing white matter damage. We hypothesised that white matter measures in regions showing HIV-related alterations will be associated with lower neurodevelopmental scores in specific domains related to the functionality of the affected tracts.

Methods

DTI was performed on children in a neurodevelopmental sub study from the Children with HIV Early Antiretroviral (CHER) trial. Voxel-based group comparisons to determine regions where fractional anisotropy and mean diffusion differed between HIV+ and uninfected children were done. Locations of clusters showing group differences were identified using the Harvard–Oxford cortical and subcortical and John Hopkins University WM tractography atlases provided in FSL. This is a second review of DTI data in this cohort, which was reported in a previous study. Neurodevelopmental assessments including GMDS and Beery-Buktenica tests were performed and correlated with DTI parameters in abnormal white matter.

Results

38 HIV+ children (14 male, mean age 64.7 months) and 11 controls (4 male, mean age 67.7 months) were imaged. Two clusters with lower fractional anisotropy and 7 clusters with increased mean diffusion were identified in the HIV+ group. The only neurodevelopmental domain with a trend of difference between the HIV+ children and controls (p = 0.08), was Personal Social Quotient which correlated to improved myelination of the forceps minor in the control group. As a combined group there was a negative correlation between visual perception and radial diffusion in the right superior longitudinal fasciculus and left inferior longitudinal fasciculus, which may be related to the fact that these tracts, forming part of the visual perception pathway, are at a crucial state of development at age 5.

Conclusion

Even directed neurodevelopmental tests will underestimate the degree of microstructural white matter damage detected by DTI. The visual perception deficit detected in the entire study population should be further examined in a larger study.

Age-related hearing loss influences functional connectivity of auditory cortex for the McGurk illusion

Age-related hearing loss affects hearing at high frequencies and is associated with difficulties in understanding speech. Increased audio-visual integration has recently been found in age-related hearing impairment, the brain mechanisms that contribute to this effect are however unclear. We used functional magnetic resonance imaging in elderly subjects with normal hearing and mild to moderate uncompensated hearing loss. Audio-visual integration was studied using the McGurk task. In this task, an illusionary fused percept can occur if incongruent auditory and visual syllables are presented. The paradigm included unisensory stimuli (auditory only, visual only), congruent audio-visual and incongruent (McGurk) audio-visual stimuli. An illusionary precept was reported in over 60% of incongruent trials. These McGurk illusion rates were equal in both groups of elderly subjects and correlated positively with speech-in-noise perception and daily listening effort. Normal-hearing participants showed an increased neural response in left pre- and postcentral gyri and right middle frontal gyrus for incongruent stimuli (McGurk) compared to congruent audio-visual stimuli. Activation patterns were however not different between groups. Task-modulated functional connectivity differed between groups showing increased connectivity from auditory cortex to visual, parietal and frontal areas in hard of hearing participants as compared to normal-hearing participants when comparing incongruent stimuli (McGurk) with congruent audio-visual stimuli. These results suggest that changes in functional connectivity of auditory cortex rather than activation strength during processing of audio-visual McGurk stimuli accompany age-related hearing loss.

Reduced Diffusion Tensor Fractional Anisotropy in the Left Arcuate Fasciculus of Patients with Aphasia Caused by Acute Cerebral Infarct

Background

Magnetic resonance diffusion tensor imaging (DTI) is a new technique that evaluates neural fiber integrity within the brain. We conducted DTI in patients exhibiting aphasia during the acute stage post-infarct and investigated the neural tracts responsible by comparison with DTI data from age-matched controls.

Methods

Fractional anisotropy (FA) maps were generated from diffusion tensor brain images obtained from aphasic patients 14-21 days following their first infarct. Tract-based spatial statistics (TBSS) analysis was then applied. In addition, regions of interest (ROIs) were set within the right and left arcuate fasciculus, and mean FA values were extracted from individual TBSS data. The ratios between FA values in the left and right hemispheres were compared with those of the control group.

Results

The study examined 10 aphasic patients and 21 age-matched controls. Brain maps from TBSS analysis revealed significantly reduced FA in the left arcuate fasciculus of the patient group compared with that in the control group. Further ROI analyses confirmed significantly lower left/right arcuate fasciculus FA ratios in aphasic patients versus controls (median [range]: 0.955 [0.739-1.023] vs. 1.006 [0.982-1.088]; P = 0.0001 by Wilcoxon rank sum test).

Conclusions

These results suggest that FA in the left arcuate fasciculus decreased in association with aphasia after cerebral infarct. Because patients in the acute stage have not yet experienced the neural recovery that occurs in the chronic stage, the findings indicate that the left arcuate fasciculus is a crucial neural structure in aphasia.

Verbal Neuropsychological Functions in Aphasia: An Integrative Model

A theoretical framework which considers the verbal functions of the brain under a multivariate and comprehensive cognitive model was statistically analyzed. A confirmatory factor analysis was performed to verify whether some recognized aphasia constructs can be hierarchically integrated as latent factors from a homogenously verbal test. The Brief Aphasia Evaluation was used. A sample of 65 patients with left cerebral lesions, and two supplementary samples comprising 35 patients with right cerebral lesions and 30 healthy participants were studied. A model encompassing an all inclusive verbal organizer and two successive organizers was validated. The two last organizers were: three factors of comprehension, expression and a "complementary" verbal factor which included praxia, attention, and memory; followed by the individual (and correlated) factors of auditory comprehension, repetition, naming, speech, reading, writing, and the "complementary" factor. By following this approach all the patients fall inside the classification system; consequently, theoretical improvement is guaranteed.

Frequency-dependent changes in the regional amplitude and synchronization of resting-state functional MRI in stroke

Resting-state functional magnetic resonance imaging (R-fMRI) has been intensively used to assess alterations of inter-regional functional connectivity in patients with stroke, but the regional properties of brain activity in stroke have not yet been fully investigated. Additionally, no study has examined a frequency effect on such regional properties in stroke patients, although this effect has been shown to play important roles in both normal brain functioning and functional abnormalities. Here we utilized R-fMRI to measure the amplitude of low-frequency fluctuations (ALFF) and regional homogeneity (ReHo), two major methods for characterizing the regional properties of R-fMRI, in three different frequency bands (slow-5: 0.01-0.027 Hz; slow-4: 0.027-0.73 Hz; and typical band: 0.01-0.1 Hz) in 19 stroke patients and 15 healthy controls. Both the ALFF and ReHo analyses revealed changes in brain activity in a number of brain regions, particularly the parietal cortex, in stroke patients compared with healthy controls. Remarkably, the regions with changed activity as detected by the slow-5 band data were more extensive, and this finding was true for both the ALFF and ReHo analyses. These results not only confirm previous studies showing abnormality in the parietal cortex in patients with stroke, but also suggest that R-fMRI studies of stroke should take frequency effects into account when measuring intrinsic brain activity.

Lesion localization of global aphasia without hemiparesis by overlapping of the brain magnetic resonance images

Global aphasia without hemiparesis is a striking stroke syndrome involving language impairment without the typically manifested contralateral hemiparesis, which is usually seen in patients with global aphasia following large left perisylvian lesions. The objective of this study is to elucidate the specific areas for lesion localization of global aphasia without hemiparesis by retrospectively studying the brain magnetic resonance images of six patients with global aphasia without hemiparesis to define global aphasia without hemiparesis-related stroke lesions before overlapping the images to visualize the most overlapped area. Talairach coordinates for the most overlapped areas were converted to corresponding anatomical regions. Lesions where the images of more than three patients overlapped were considered significant. The overlapped global aphasia without hemiparesis related stroke lesions of six patients revealed that the significantly involved anatomical lesions were as follows: frontal lobe, sub-gyral, sub-lobar, extra-nuclear, corpus callosum, and inferior frontal gyrus, while caudate, claustrum, middle frontal gyrus, limbic lobe, temporal lobe, superior temporal gyrus, uncus, anterior cingulate, parahippocampal, amygdala, and subcallosal gyrus were seen less significantly involved. This study is the first to demonstrate the heterogeneous anatomical involvement in global aphasia without hemiparesis by overlapping of the brain magnetic resonance images.

Aphasia severity in chronic stroke patients: a combined disconnection in the dorsal and ventral language pathways

BACKGROUND

The contribution of lesion size and location in poststroke aphasia is debated, especially the extent to which aphasia severity is affected by damage to specific white matter areas.

OBJECTIVE

To identify specific white matter areas critical for poststroke aphasia global severity and to determine whether injury to these areas had more impact on aphasia severity than the infarct volume.

METHODS

Twenty-three chronic poststroke aphasic patients were assessed with the Aphasia Rapid Test (ART) and the Boston Diagnosis Aphasia Examination (BDAE) global severity scales and underwent diffusion tensor and structural imaging. Voxel-based diffusion tensor imaging regression analysis was used to determine in which areas fractional anisotropy (FA) abnormalities were correlated with ART and BDAE severity scales. The relationships between aphasia severity, FA values, and infarct volumes were investigated using global and partial correlations.

RESULTS

We found a critical area associated with aphasia severity overlapping with the arcuate and the inferior fronto-occipital fasciculi, resulting in a combined disconnection of the dorsal and ventral pathways. ART scores were inversely correlated with FA values in this region, with greater severity present with lower FA values (correlation coefficient = -0.833, P < .0001). The proportion of variance explained by the FA value was higher than the proportion of variance explained by the infarct volume (R (2) = 68% vs 27%, P = .01). The impact of infarct volume on aphasia severity disappeared when damage to this critical white matter area was taken into account (P = .38).

CONCLUSION

The assessment of the integrity of this region may potentially have a clinical impact in neurorehabilitation and acute decision making.

White matter tracts of speech and language

Diffusion tensor imaging (DTI) has been used to investigate the white matter (WM) tracts underlying the perisylvian cortical regions known to be associated with language function. The arcuate fasciculus is composed of 3 segments (1 long and 2 short) whose separate functions correlate with traditional models of conductive and transcortical motor or sensory aphasia, respectively. DTI mapping of language fibers is useful in presurgical planning for patients with dominant hemisphere tumors, particularly when combined with functional magnetic resonance imaging. DTI has found damage to language networks in stroke patients and has the potential to influence poststroke rehabilitation and treatment. Assessment of the WM tracts involved in the default mode network has been found to correlate with mild cognitive impairment, potentially explaining language deficits in patients with apparently mild small vessel ischemic disease. Different patterns of involvement of language-related WM structures appear to correlate with different clinical subtypes of primary progressive aphasias.

Why is it difficult to predict language impairment and outcome in patients with aphasia after stroke?

One of the most devastating consequences of stroke is aphasia. Communication problems after stroke can severely impair the patient's quality of life and make even simple everyday tasks challenging. Despite intense research in the field of aphasiology, the type of language impairment has not yet been localized and correlated with brain damage, making it difficult to predict the language outcome for stroke patients with aphasia. Our primary objective is to present the available evidence that highlights the difficulties of predicting language impairment after stroke. The different levels of complexity involved in predicting the lesion site from language impairment and ultimately predicting the long-term outcome in stroke patients with aphasia were explored. Future directions and potential implications for research and clinical practice are highlighted.

Diffusion magnetic resonance imaging for Brainnetome: a critical review

Increasing evidence shows that the human brain is a highly self-organized system that shows attributes of small-worldness, hierarchy and modularity. The "connectome" was conceived several years ago to identify the underpinning physical connectivities of brain networks. The need for an integration of multi-spatial and -temporal approaches is becoming apparent. Therefore, the "Brainnetome" (brain-net-ome) project was proposed. Diffusion magnetic resonance imaging (dMRI) is a non-invasive way to study the anatomy of brain networks. Here, we review the principles of dMRI, its methodologies, and some of its clinical applications for the Brainnetome. Future research in this field is discussed.