Using transcranial direct current stimulation (tDCS) to treat persons with aphasia

Increased left hemisphere cortical activity, primarily of the frontal cortex, is associated with improved naming performance in persons with aphasia (PWA). Our aim was to determine if anodal transcranial direct current stimulation (A-tDCS), a noninvasive and safe method used to increase cortical excitability, would improve naming accuracy in PWA when applied to the scalp overlying the left frontal cortex. Ten PWA received five days of A-tDCS (1 mA; 20 min) and five days of sham tDCS (S-tDCS) while performing a computerized anomia treatment. Results revealed significantly improved naming accuracy of treated and untreated items following A-tDCS as compared to S-tDCS

Brain damage associated with impaired repetition

The classical view of aphasia suggests that conduction aphasia results from disconnection between the anterior and posterior language areas. Several recent reports have challenged this claim suggesting that impaired repetition – the hallmark symptom of conduction aphasia – is associated with damaged gray matter in the left parietal lobe. This study examined the critical lesion location associated with impaired repetition in 44 acute left hemisphere stroke patients. We found that damage to the posterior portion of the left arcuate fasciculus is the best neuroanatomical predictor of impaired repetition. These results support the classical view of conduction aphasia as a disconnection syndrome

Temporal order processing of syllables in the left parietal lobe

Speech processing requires the temporal parsing of syllable order. Individuals suffering from posterior left hemisphere brain injury often exhibit temporal processing deficits as well as language deficits. Although the right posterior inferior parietal lobe has been implicated in temporal order judgments (TOJs) of visual information, there is limited evidence to support the role of the left inferior parietal lobe (IPL) in processing syllable order. The purpose of this study was to examine whether the left inferior parietal lobe is recruited during temporal order judgments of speech stimuli. Functional magnetic resonance imaging data were collected on 14 normal participants while they completed the following forced-choice tasks: (1) syllable order of multisyllabic pseudowords, (2) syllable identification of single syllables, and (3) gender identification of both multisyllabic and monosyllabic speech stimuli. Results revealed increased neural recruitment in the left inferior parietal lobe when participants made judgments about syllable order compared with both syllable identification and gender identification. These findings suggest that the left inferior parietal lobe plays an important role in processing syllable order and support the hypothesized role of this region as an interface between auditory speech and the articulatory code. Furthermore, a breakdown in this interface may explain some components of the speech deficits observed after posterior damage to the left hemisphere

Using neuroimaging to classify aphasia

The proper classification of aphasia based on clinical symptoms has been debated for well over a century. Much of the early debates centered on relating localized brain damage to a constellation of speech and language impairments. The premise behind much of this work was based on the notion that lesion-symptom mapping could reveal how language was organized in the brain (Broca, 1861, 1865; Dejarine, 1906; Marie, 1906). Although the principle for classifying aphasia based on specific symptoms has been fervently challenged (e.g. Head, 1926) it is still customary to report aphasia types in clinical studies of aphasia. Similar symptoms in sub-groups of patients suggests a similar pattern of brain damage. Nevertheless, it remains unclear if specific aphasia types can be diagnosed simply based on the location of cortical damage. One way to examine this issue would be to relate lesion patterns to aphasia types using multivariate pattern analysis (MVPA). MVPA of neuroimaging data has been successfully used to diagnose diseases such as dementia, schizophrenia, and Parkinson's disease (Orru et al., 2012). In the present study, we demonstrate how MVPA can be used to predict aphasia type in persons with chronic stroke. Unlike previous studies that perform the analysis on voxels (using MRI scans), we trained a classifier on the proportional damage to brain areas (defined with a brain atlas). In addition, we computed the loadings that reflect the contribution of each brain area to classification

Localizing unique and overlapping lesion locations in apraxia of speech and aphasia

Since Darley’s original description of apraxia of speech (AOS; 1968), controversy has centered around its diagnosis, treatment, and lesion location. Behaviors common to AOS are often shared among other communication disorders, complicating clinical management. The current study sought to identify crucial brain damage that causes apraxic speech, as well as errors common in both AOS and aphasia. Results revealed that damage to premotor and supplementary motor areas is unique to AOS, while involvement of temporal lobe areas predicts behaviors attributable to aphasia. These findings contribute to research regarding the neuroanatomical mechanism of AOS, and may ultimately improve differential diagnostic procedures

False discovery rate control for lesion-symptom mapping with heterogeneous data via weighted p-values

Statistic

Cortical mapping of naming errors in aphasia

This study utilized fMRI to examine neurological activity associated with picture naming in twelve persons with chronic aphasia. A group fMRI analysis revealed common neurological activity associated the production of phonemic paraphasias in the posterior perilesional parietal and occipital areas. Semantic paraphasias recruited a wide-spread cortical network including, among others, the bilateral inferior temporal lobule as well as spared cortical areas in the left frontal lobe. These findings suggest that common cortical areas are modulated during the productions of naming errors in aphasic patients; even those with different types and severity of aphasia

Current Approaches to the Treatment of Post-stroke Aphasia

Aphasia, impairment of language after stroke or other neurological insult, is a common and often devastating condition that affects nearly every social activity and interaction. Behavioral speech and language therapy is the mainstay of treatment, although other interventions have been introduced to augment the effects of the behavioral therapy. In this narrative review, we discuss advances in aphasia therapy in the last 5 years and focus primarily on properly powered, randomized, controlled trials of both behavioral therapies and interventions to augment therapy for post-stroke aphasia. These trials include evaluation of behavioral therapies and computer-delivered language therapies. We also discuss outcome prediction trials as well as interventional trials that have employed noninvasive brain stimulation, or medications to augment language therapy. Supported by evidence from Phase III trials and large meta-analyses, it is now generally accepted that aphasia therapy can improve language processing for many patients. Not all patients respond similarly to aphasia therapy with the most severe patients being the least likely responders. Nevertheless, it is imperative that all patients, regardless of severity, receive aphasia management focused on direct therapy of language deficits, counseling, or both. Emerging evidence from Phase II trials suggests transcranial brain stimulation is a promising method to boost aphasia therapy outcomes

False Discovery Rate Control for Lesion-Symptom Mapping with Heterogeneous data via Weighted P-values

Lesion-symptom mapping studies provide insight into what areas of the brain are involved in different aspects of cognition. This is commonly done via behavioral testing in patients with a naturally occurring brain injury or lesions (e.g., strokes or brain tumors). This results in high-dimensional observational data where lesion status (present/absent) is non-uniformly distributed with some voxels having lesions in very few (or no) subjects. In this situation, mass univariate hypothesis tests have severe power heterogeneity where many tests are known a priori to have little to no power. Recent advancements in multiple testing methodologies allow researchers to weigh hypotheses according to side-information (e.g., information on power heterogeneity). In this paper, we propose the use of p-value weighting for voxel-based lesion-symptom mapping (VLSM) studies. The weights are created using the distribution of lesion status and spatial information to estimate different non-null prior probabilities for each hypothesis test through some common approaches. We provide a monotone minimum weight criterion which requires minimum a priori power information. Our methods are demonstrated on dependent simulated data and an aphasia study investigating which regions of the brain are associated with the severity of language impairment among stroke survivors. The results demonstrate that the proposed methods have robust error control and can increase power. Further, we showcase how weights can be used to identify regions that are inconclusive due to lack of power

Localizing lesion locations to predict extent of aphasia recovery

Extensive research has related specific lesion locations to language impairment in aphasia. However, far less work has focused on the patterns of brain damage that predict prognosis in aphasia. The current study examined brain damage as a predictor of language recovery in acute patients with aphasia caused by stroke. Damage to the left posterior middle temporal gyrus (MTG) and left pars triangularis predicted poor recovery of speech production and MTG damage predicted less recovery of speech comprehension. These findings suggest that brain changes associated with language recovery rely on preservation and recruitment of the aforementioned areas in the left hemisphere