Through Thick and Thin: Baseline Cortical Volume and Thickness Predict Performance and Response to Transcranial Direct Current Stimulation in Primary Progressive Aphasia.

Objectives: We hypothesized that measures of cortical thickness and volume in language areas would correlate with response to treatment with high-definition transcranial direct current stimulation (HD-tDCS) in persons with primary progressive aphasia (PPA). Materials and Methods: In a blinded, within-group crossover study, PPA patients (N = 12) underwent a 2-week intervention HD-tDCS paired with constraint-induced language therapy (CILT). Multi-level linear regression (backward-fitted models) were performed to assess cortical measures as predictors of tDCS-induced naming improvements, measured by the Western Aphasia Battery-naming subtest, from baseline to immediately after and 6 weeks post-intervention. Results: Greater baseline thickness of the pars opercularis significantly predicted naming gains (p = 0.03) immediately following intervention, while greater thickness of the middle temporal gyrus (MTG) and lower thickness of the superior temporal gyrus (STG) significantly predicted 6-week naming gains (p's < 0.02). Thickness did not predict naming gains in sham. Volume did not predict immediate gains for active stimulation. Greater volume of the pars triangularis and MTG, but lower STG volume significantly predicted 6-week naming gains in active stimulation. Greater pars orbitalis and MTG volume, and lower STG volume predicted immediate naming gains in sham (p's < 0.05). Volume did not predict 6-week naming gains in sham. Conclusion: Cortical thickness and volume were predictive of tDCS-induced naming improvement in PPA patients. The finding that frontal thickness predicted immediate active tDCS-induced naming gains while temporal areas predicted naming changes at 6-week suggests that a broader network of regions may be important for long-term maintenance of treatment gains. The finding that volume predicted immediate naming performance in the sham condition may reflect the benefits of behavioral speech language therapy and neural correlates of its short-lived treatment gains. Collectively, thickness and volume were predictive of treatment gains in the active condition but not sham, suggesting that pairing HD-tDCS with CILT may be important for maintaining treatment effects.

Higher Cardiorespiratory Fitness is Associated with Reduced Functional Brain Connectivity During Performance of the Stroop Task.

BACKGROUND: Although higher cardiorespiratory fitness (CRF) has been linked to better executive function, the mechanisms by which this occurs remain a matter of speculation. One hypothesis is that higher CRF is associated with elevated top-down control in which brain regions processing task-relevant information are up-regulated and brain regions processing task-irrelevant information are down-regulated. METHODS: We tested this top-down hypothesis in 50 young adults (µ age = 25.22 ±â€Š5.17 years) by measuring CRF via a graded maximal exercise test and performing functional Magnetic Resonance Imaging (fMRI) during a color-word Stroop task. We used task-evoked functional connectivity, quantified from a psychophysiological interaction analysis (PPI), to test our hypotheses that (a) higher CRF would be associated with greater connectivity between control centers (i.e., prefrontal and parietal areas) and visual feature centers (i.e., occipital areas) that are involved with processing task-relevant stimulus dimensions (i.e., color), and (b) higher CRF would be associated with lower connectivity between control centers and visual feature centers that are involved with processing task-irrelevant dimensions of the stimuli (i.e., word processing areas). RESULTS: Controlling for sex and BMI, we found, consistent with our second hypothesis, that higher CRF was associated with reduced functional connectivity between parietal and occipital areas involved in the task-irrelevant dimension of the task (i.e., word form areas). There were no associations between CRF and functional connectivity with the prefrontal cortex or evidence of heightened connectivity between attentional control and visual feature centers. CONCLUSIONS: These results suggest that CRF associations with executive functioning might be explained by CRF-mediated differences between brain regions involved with attentional control (parietal regions) and the down-regulation of regions involved with processing task-irrelevant stimulus features (occipital regions).