Recovering two languages with the right hemisphere

Distinct brain morphometry patterns revealed by deep learning improve prediction of post-stroke aphasia severity

BACKGROUND

Emerging evidence suggests that post-stroke aphasia severity depends on the integrity of the brain beyond the lesion. While measures of lesion anatomy and brain integrity combine synergistically to explain aphasic symptoms, substantial interindividual variability remains unaccounted. One explanatory factor may be the spatial distribution of morphometry beyond the lesion (e.g., atrophy), including not just specific brain areas, but distinct three-dimensional patterns.

METHODS

Here, we test whether deep learning with Convolutional Neural Networks (CNNs) on whole brain morphometry (i.e., segmented tissue volumes) and lesion anatomy better predicts chronic stroke individuals with severe aphasia (N = 231) than classical machine learning (Support Vector Machines; SVMs), evaluating whether encoding spatial dependencies identifies uniquely predictive patterns.

RESULTS

CNNs achieve higher balanced accuracy and F1 scores, even when SVMs are nonlinear or integrate linear or nonlinear dimensionality reduction. Parity only occurs when SVMs access features learned by CNNs. Saliency maps demonstrate that CNNs leverage distributed morphometry patterns, whereas SVMs focus on the area around the lesion. Ensemble clustering of CNN saliencies reveals distinct morphometry patterns unrelated to lesion size, consistent across individuals, and which implicate unique networks associated with different cognitive processes as measured by the wider neuroimaging literature. Individualized predictions depend on both ipsilateral and contralateral features outside the lesion.

CONCLUSIONS

Three-dimensional network distributions of morphometry are directly associated with aphasia severity, underscoring the potential for CNNs to improve outcome prognostication from neuroimaging data, and highlighting the prospective benefits of interrogating spatial dependence at different scales in multivariate feature space.

Individual differences and creative ideation: neuromodulatory signatures of mindset and response inhibition

This study addresses the modulatory role of individual mindset in explaining the relationship between response inhibition (RI) and divergent thinking (DT) using transcranial direct current stimulation (tDCS). Forty undergraduate students (22 male and 18 female), aged between 18 and 23 years (average age = 19 years, SD = 1.48), were recruited. Participants received either anodal tDCS of the right IFG coupled with cathodal tDCS of the left IFG (R + L-; N = 19) or the opposite coupling (R-L+; N = 21). We tested DT performance using the alternative uses task (AUT), measuring participants' fluency, originality, and flexibility in the response production, as well as participants' mindsets. Furthermore, we applied a go-no-go task to examine the role of RI before and after stimulating the inferior frontal gyrus (IFG) using tDCS. The results showed that the mindset levels acted as moderators on stimulation conditions and enhanced RI on AUT fluency and flexibility but not originality. Intriguingly, growth mindsets have opposite moderating effects on the change in DT, resulting from the tDCS stimulation of the left and the right IFG, with reduced fluency but enhanced flexibility. Our findings imply that understanding neural modulatory signatures of ideational processes with tDCS strongly benefits from evaluating cognitive status and control functions.

[Crossed aphasia in neurosurgical practice: case report and literature review]

BACKGROUND

Crossed aphasia in dexstral (CAD) is an extremely rare disorder. To date, about 200 cases have been described in the literature.

MATERIAL AND METHODS

The authors report 4 cases of CAD. Luria's neuropsychological examination was carried out. Functional asymmetry in the arm was analyzed using the Annett questionnaire. MRI and intraoperative findings confirmed localization of lesion in the right hemisphere in all patients.

RESULTS

A 59-year-old right-handed man developed frontotemporal aphasia after previous resection of right-sided glioblastoma of fronto-insular-temporal region. In a 31-year-old right-handed man, crossed aphasia occurred after extensive hemorrhage from arteriovenous malformation into the right frontotemporoparietal region. A 39-year-old right-handed man developed severe combined aphasia after resection of diffuse glioma of the right insular-temporal region. A 10-year-old right-handed boy developed aphasia with word forgetting after resection of a large tumor of the right temporal lobe. All patients had impaired dynamic praxis. Other cognitive functions were intact.

CONCLUSION

The authors discuss possible combinations of functions in one hemisphere for both right-handers and left-handers and emphasize diverse types of functional asymmetries described in the literature. Different localizations of functions in right-handers and left-handers indicate that local zones with different methods of information processing (successive or simultaneous) can coexist in one hemisphere. Therefore, the functions requiring different processing of information (for example, speech with praxis or spatial functions) can develop in one hemisphere. Cognitive impairment depends not only on the type of functional asymmetry, but also on localization of lesion. Crossed aphasia in right-handers indicates the rarest normal type of functional brain asymmetry with localization of speech functions in the right hemisphere. Possible aphasia in right-handers following damage to homologues of speech zones in the right hemisphere can require additional examination of these patients.

Transcranial Direct-Current Stimulation and Behavioral Training, a Promising Tool for a Tailor-Made Post-stroke Aphasia Rehabilitation: A Review

Aphasia is an acquired language disorder resulting from damage to portions of the brain which are responsible for language comprehension and formulation. This disorder can involve different levels of language processing with impairments in both oral and written comprehension and production. Over the last years, different rehabilitation and therapeutic interventions have been developed, especially non-invasive brain stimulation (NIBS) techniques. One of the most used NIBS techniques in aphasia rehabilitation is the Transcranial Direct-Current Stimulation (tDCS). It has been proven to be effective in promoting a successful recovery both in the short and the long term after a brain injury. The main strength of tDCS is its feasibility associated with relatively minor side effects, if safely and properly administered. TDCS requires two electrodes, an anode and a cathode, which are generally placed on the scalp. The electrode montage can be either unipolar or bipolar. The main aim of this review is to give an overview of the state of the art of tDCS for the treatment of aphasia. The studies described included patients with different types of language impairments, especially with non-fluent aphasia and in several cases anomia. The effects of tDCS are variable and depend on several factors, such as electrode size and montage, duration of the stimulation, current density and characteristics of the brain tissue underneath the electrodes. Generally, tDCS has led to promising results in rehabilitating patients with acquired aphasia, especially if combined with different language and communication therapies. The selection of the appropriate approach depends on the patients treated and their impaired language function. When used in combination with treatments such as Speech and Language Therapy, Constraint Induced Aphasia Therapy or Intensive Action Treatment, tDCS has generally promoted a better recovery of the impaired functions. In addition to these rehabilitation protocols, Action Observation Therapy, such as IMITAF, appeared to contribute to the reduction of post-stroke anomia. The potential of combining such techniques with tDCS would would therefore be a possibility for further improvement, also providing the clinician with a new action and intervention tool. The association of a tDCS protocol with a dedicated rehabilitation training would favor a generalized long-term improvement of the different components of language.

Verbal fluency in three Spanish-English bilingual speakers with TBI

This study investigated differences between healthy bilingual participants and bilingual participants with traumatic brain injury (TBI) on verbal fluency tasks. The performance of three Spanish-English bilingual speakers with traumatic brain injury was compared to the performance of 30 neurotypical bilingual speakers on tasks of category and letter verbal fluency in English and Spanish. Responses were analyzed for total number of correct productions, differences in correct productions between languages, average cluster size, total number of switches, and rates of language choice errors. The data were analyzed using predicted scores from regression equations based on neurotypical data and modified t-tests. Analyses revealed significantly lower total output than predicted by the regression equations for both task types and in both languages for one TBI participant. The same participant demonstrated significantly lower total number of switches than the neurotypical group. Two participants demonstrated higher rates of language choice errors than the neurotypical group. There were no significant differences between TBI participants and the neurotypical group for average cluster size. There were no significant differences between predicted and obtained values for differences between English and Spanish total number correct in each task type. Results are discussed in the context of individual cognitive and linguistic profiles of the TBI participants.