We investigated the role of serotonin in cognitive activation of the frontal cortex. The serotonergic system was affected by the administration of an amino acids mixture without tryptophan (tryptophan depletion). In a placebo-controlled double-blind cross-over study with 20 healthy volunteers, we tested the hypothesis that a tryptophan (serotonin)
decrease affects the activation of prefrontal cortex by the Stroop test. Cognitive brain activation was evaluated by functional magnetic resonance imaging (fMRI). Tryptophan depletion decreased the plasma tryptophan level up to 90 % for five hours after the tryptophan-free drink had been consumed when compared with the same mixture with tryptophan (p ≤
0.0001). Tryptophan depletion did not affect the Stroop test performance. We compared fMRI activation in both conditions (tryptophan depletion and placebo) with plasma tryptophan levels as the covariates. The tryptophan
depletion increased the activation (fMRI signal) in the bilateral mediofrontal cortex, anterior cingulate and left dorsolateral prefrontal cortex. The present findings allow the postulate that serotonergic medial forebrain and cingulum bundle pathways play a role in the activity of cortical structures involved in Stroop test processing.
Brain imaging studies suggest localization of verbal working memory in the left dorsolateral prefrontal cortex (DLPFC) while face processing and memory is localized in the inferior temporal cortex and other brain areas. The goal of this study was to assess the effect of left DLPFC low-frequency repetitive transcranial magnetic stimulation (rTMS) on
verbal recall and face recognition. The study revealed a significant decrease of free recall in word encoding under rTMS (110 % of motor threshold, 0.9 Hz) in comparison with sham stimulation (p=0.03), while no significant difference was found with facial memory tests. Our findings support the essential role of the left DLPFC in word but not facial memory and confirm the content specific arrangement of cortical areas involved in semantic memory. As a non-invasive tool, rTMS is useful for cognitive brain mapping and the functional localization of the category specific memory system.
Numerous abnormalities of thyroid hormones in end-stage renal disease (ESRD) have been described. Our aim was to analyze the impact of these abnormalities on survival. In 167 hemodialyzed ESRD patients, TSH and thyroid hormone levels (T4, fT4, T3, fT3, rT3) were determined. The patients were then prospectively followed up for up to 5 years and the possible impact of any observed abnormalities on their mortality was studied. Only 16.8 % patients had all six tests within the reference range. The pattern of nonthyroidal illness syndrome was found in 56.3 %. Low T3 was particularly common (44.3 %), and clearly associated with increased 6- and 12-month mortality and decreased overall survival (log rank test, P=0.007). Independent of T3 levels (Spearman correlation, NS), increased rT3 was more frequently observed (9.9 %) than expected from the literature, and was also related to increased mortality and decreased survival (log rank test, P=0.021). Increased rT3 may be more common in ESRD patients than previously described, and together with decreased T3 it may serve as an indicator of poor prognosis in subsequent months., J. Horáček ... [et al.]., and Obsahuje seznam literatury