Recent results from diffusion tensor imaging (DTI) studies provide evidence of a ventral-lexical stream and a dorsal-sublexical stream associated with reading processing. We investigated the relationship between behavioural reading speed for stimuli thought to rely on either the ventral-lexical, dorsal-sublexical, or both streams and white matter via fractional anisotropy (FA) and mean diffusivity (MD) using DTI tractography. Participants (N = 32) overtly named exception words (e.g., 'one', ventral-lexical), regular words (e.g., 'won', both streams), nonwords ('wum', dorsal-sublexical) and pseudohomophones ('wun', dorsal-sublexical) in a behavioural lab. Each participant then underwent a brain scan that included a 30-directional DTI sequence. Tractography was used to extract FA and MD values from four tracts of interest: inferior longitudinal fasciculus, uncinate fasciculus, arcuate fasciculus, and inferior fronto-occipital fasciculus. Median reaction times (RTs) for reading exception words and regular words both showed a significant correlation with the FA of the uncinate fasciculus thought to underlie the ventral processing stream, such that response time decreased as FA increased. In addition, RT for exception and regular words showed a relationship with MD of the uncinate fasciculus, such that response time increased as MD increased. Multiple regression analyses revealed that exception word RT accounted for unique variability in FA of the uncinate over and above regular words. There were no robust relationships found between pseudohomophones, or nonwords, and tracts thought to underlie the dorsal processing stream. These results support the notion that word recognition, in general, and exception word reading in particular, rely on ventral-lexical brain regions.
BackgroundAlthough repetitive transcranial magnetic stimulation (rTMS) has been extensively studied in patients with Alzheimer's disease (AD), the clinical evidence remains inconsistent. The purpose of this meta-analysis was to evaluate the effects of rTMS on global cognitive function in patients with AD.MethodsAn integrated literature search using 4 databases (PubMed, Web of Science, Embase, and Cochrane Library) was performed to identify English language articles published up to October 6, 2021. We pooled Mini-Mental State Examination (MMSE) and Alzheimer's Disease Assessment Scale-cognitive subscale (ADAS-Cog) scores using a random-effects model via RevMan 5.4 software. We calculated estimates of mean differences (MD) with 95% confidence intervals (CI). The primary outcomes were pre-post treatment changes in global cognition as measured using MMSE and ADAS-Cog immediately after rTMS treatment, and the secondary outcome was duration of cognitive improvement (1–1.5 and ≥3 months).ResultsNine studies with 361 patients were included in this meta-analysis. The results showed that rTMS significantly improved global cognitive function immediately following rTMS treatment [(MD) 1.82, 95% confidence interval (CI) 1.41–2.22, p < 0.00001, MMSE; 2.72, 95% CI, 1.77–3.67, p < 0.00001, ADAS-Cog], and the therapeutic effects persisted for an extended duration (2.20, 95% CI, 0.93–3.47, p =0.0007, MMSE; 1.96, 95% CI, 0.96–2.95, p = 0.0001, ADAS-Cog). Subgroup analyses showed that high frequency rTMS targeted to the left dorsolateral prefrontal cortex (DLPFC) for over 20 sessions induced the greatest cognitive improvement, with effects lasting for more than 1 month after the final treatment. There were no significant differences in dropout rate (p > 0.05) or adverse effect rate (p > 0.05) between the rTMS and control groups.ConclusionsRepetitive TMS is a potentially effective treatment for cognitive impairment in AD that is safe and can induce long-lasting effects. Our results also showed that ADAS-cog and MMSE differed in determination of global cognitive impairment.Systematic review registrationhttp://www.crd.york.ac.uk/PROSPERO, PROSPERO CRD42022315545.
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