Effects of Methylene Blue in Healthy Aging, Mild Cognitive Impairment and Alzheimer's Disease

Healthy aging and aging human subjects with mild cognitive impairment and mild Alzheimer's disease from the TARCC cohort and South Texas will be studied using a double-blind, placebo-controlled design. After informed consent and familiarity with the tasks and the MRI environment, the subject will enter an MRI scanner and perform the following 6 tasks. fMRI and behavioral data will be collected simultaneously while inside the scanner. Delayed match-to-sample task: The subject views a pattern for a few seconds and then is prompted to recall the memorized pattern using a response system (approx. 10 mins). Face-name task: The subject is shown blocks of stimuli where a novel or familiar face is paired with a name. In a later run, the subjects are asked whether the correct name is matched with the correct face. (approx. 10 mins). Psychomotor vigilance task: The subject receives a visual cue that alerts them to press a button as fast as possible. (approx. 10 mins). Cerebral Blood Flow and Resting State fMRI: Subject scanned with eyes closed and told to not think about a particular topic, each lasting about 10 minutes. fMRI data acquisition: fMRI and neuropsychological battery measurements will be made before the intervention. These measurements will then be repeated after 2 weeks and 12 weeks. fMRI will image changes in regional brain activity associated with these tasks. The MRI pulse sequences include diffusion tensor imaging, standard and non-invasive anatomical and quantitative MRI for coregistration and blood-oxygen-level dependent (BOLD) fMRI. CO2 challenge: Cerebral blood flow measurements will be obtained while the subject rests in the scanner after administration of medical-grade 5% CO2 in air for 3-5 minutes. This will be repeated on weeks 2 and 12. Data analysis: Standard fMRI analysis will be analyzed using established fMRI software. Statistical parametric analysis will be performed to generate activation maps. fMRI data will be corrected for multiple comparisons using a false discovery rate (q \< 0.05) and threshold for cluster values to conservatively control for type I error. Behavioral data will be analyzed with paired t-test and ANOVA calculations used for group comparison with p \< 0.05 (with Bonferroni correction) considered statistically significant. Expected results: The investigators predict that, compared to placebo, MB will: i) improve working memory retention in a delayed match-to-sample task by memory performance and enhanced fMRI responses in the prefrontal cortex and parietal lobes, ii) improve episodic memory as determined by fMRI activation in the hippocampus, medial temporal lobes and prefrontal cortex iii) reduce reaction time in a psychomotor vigilance test and enhance fMRI responses within a cortical sustained attention network iv) improve CBF and v) improve fMRI connectivity in default mode and visuospatial and memory networks/subnetworks. The fMRI and behavioral performance effects on memory will be greater in the MCI and mild AD groups than in the healthy aging group. The effects will be greater in the MCI and AD groups than in the control groups. Power analysis: Sample sizes were calculated using an fMRI power tool based on pilot data from the current study for a power of 80%, alpha = 0.05, False Discovery Rate \< 0.05, to detect statistical difference between MB and placebo23. The investigators estimate they will need 20-25 subjects per arm of group (complete studies) and thus will recruit 200-240 subjects to account for potential failed studies.