The unique role of the frontal aslant tract in speech and language processing.

The frontal aslant tract (FAT) is a recently described intralobar tract that connects the superior and inferior frontal gyri. The FAT has been implicated in various speech and language processes and disorders, including motor speech impairments, stuttering disorders, opercular syndrome, and verbal fluency, but the specific function(s) of the FAT have yet to be elucidated. In the current study, we aimed to address this knowledge gap by investigating the underlying role that the FAT plays in motor aspects of speech and language abilities in post-stroke aphasia. Our goals were three-fold: 1) To identify which specific motor speech or language abilities are impacted by FAT damage by utilizing a powerful imaging analysis method, High Angular Resolution Diffusion Imaging (HARDI) tractography; 2) To determine whether damage to the FAT is associated with functional deficits on a range of motor speech and language tasks even when accounting for cortical damage to adjacent cortical regions; and 3) To explore whether subsections of the FAT (lateral and medial segments) play distinct roles in motor speech performance. We hypothesized that damage to the FAT would be most strongly associated with motor speech performance in comparison to language tasks. We analyzed HARDI data from thirty-three people with aphasia (PWA) with a history of chronic left hemisphere stroke. FAT metrics were related to scores on several speech and language tests: the Motor Speech Evaluation (MSE), the Western Aphasia Battery (WAB) aphasia quotient and subtests, and the Boston Naming Test (BNT). Our results indicated that the integrity of the FAT was strongly associated with the MSE as predicted, and weakly negatively associated with WAB subtest scores including Naming, Comprehension, and Repetition, likely reflecting the fact that performance on these WAB subtests is associated with damage to posterior areas of the brain that are unlikely to be damaged with a frontal lesion. We also performed hierarchical stepwise regressions to predict language function based on FAT properties and lesion load to surrounding cortical areas. After accounting for the contributions of the inferior frontal gyrus, the ventral precentral gyrus, and the superior precentral gyrus of the insula, the FAT still remained a significant predictor of MSE apraxia scores. Our results further showed that the medial and lateral subsections of the FAT did not appear to play distinct roles but rather may indicate normal anatomical variations of the FAT. Overall, current results indicate that the FAT plays a specific and unique role in motor speech. These results further our understanding of the role that white matter tracts play in speech and language.

Transcarotid Access for Mechanical Thrombectomy in Acute Ischemic Stroke: A Meta-Analysis and Systematic Review.

OBJECTIVES: Despite the success of mechanical thrombectomy in large vessel acute ischemic stroke, recanalization may fail due to difficult anatomic access or peripheral arterial occlusive disease. In these cases, transcarotid access may be used as an alternative, but it has not gained prominence due to safety concerns. Our objective was to assess the efficacy and safety of transcarotid access for mechanical thrombectomy. MATERIALS AND METHODS: Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were used to perform a systematic review with articles published from 2010 to 2020 summarizing pre-intervention characteristics, techniques utilized, and outcomes of patients undergoing mechanical thrombectomy via trans-carotid puncture. We performed a meta-analysis of clinical outcomes, reperfusion times and overall complications rates of trans-carotid approach. RESULTS: Six studies describing 80 total attempts at carotid access, 72 of which were successful (90% success rate), were included. Direct carotid puncture was most often used as a rescue technique (87% of patients) secondary to failed femoral access. Successful recanalization was achieved in 76% of patients. 90 day modified Rankin Scale ≤ 2 was achieved in 28% of patients. Carotid puncture-reperfusion time was 32 min (CI = 24-40, p < 0.001). Cervical complications occurred at a rate of 26.5% (95% CI = 17%-38%). Only 1.3% (1/80 patients) had a fatal outcome and 96% of complications required no intervention. CONCLUSIONS: Our results on the safety and efficacy of transcarotid access suggests that this approach is a viable alternative to failed thrombectomy when transfemoral or trans-radial access may be impractical.

Brain microstructure mediates sex-specific patterns of cognitive aging.

Normal brain aging is characterized by declining neuronal integrity, yet it remains unclear how microstructural injury influences cognitive aging and whether such mechanisms differ between sexes. Using restriction spectrum imaging (RSI), we examined sex differences in associations between brain microstructure and cognitive function in 147 community-dwelling older men and women (56-99 years). Gray and white matter microstructure correlated with global cognition, executive function, visuospatial memory, episodic memory, and logical memory, with the strongest associations for restricted, hindered and free isotropic diffusion. Associations were stronger for women than for men, a difference likely due to greater age-related variability in cognitive scores and microstructure in women. Isotropic diffusion mediated effects of age on cognition for both sexes, though distinct mediation patterns were present for women and men. For women, hippocampal and corpus callosum microstructure mediated age effects on verbal and visuospatial memory, respectively, whereas for men fiber microstructure (mainly fornix and corpus callosum) mediated age effects on executive function and visuospatial memory. These findings implicate sex-specific pathways by which changing brain cytoarchitecture contributes to cognitive aging, and suggest that RSI may be useful for evaluating risk for cognitive decline or monitoring efficacy of interventions to preserve brain health in later life.