Hierarchical clustering to measure connectivity in fMRI resting-state data.

Low frequency oscillations, which are temporally correlated in functionally related brain regions, characterize the mammalian brain, even when no explicit cognitive tasks are performed. Functional connectivity MR imaging is used to map regions of the resting brain showing synchronous, regional and slow fluctuations in cerebral blood flow and oxygenation. In this study, we use a hierarchical clustering method to detect similarities of low-frequency fluctuations. We describe one measure of correlations in the low frequency range for classification of resting-state fMRI data. Furthermore, we investigate the contribution of motion and hardware instabilities to resting-state correlations and provide a method to reduce artifacts. For all cortical regions studied and clusters obtained, we quantify the degree of contamination of functional connectivity maps by the respiratory and cardiac cycle. Results indicate that patterns of functional connectivity can be obtained with hierarchical clustering that resemble known neuronal connections. The corresponding voxel time series do not show significant correlations in the respiratory or cardiac frequency band.

Activity of P-Glycoprotein, a ß-Amyloid Transporter at the Blood-Brain Barrier, Is Compromised in Patients with Mild Alzheimer Disease.

UNLABELLED: Studies in animals and postmortem human brain tissue support a role for P-glycoprotein in clearance of cerebral ß-amyloid across the blood-brain barrier (BBB). We tested the hypothesis that BBB P-glycoprotein activity is diminished in Alzheimer disease (AD) by accounting for an AD-related reduction in regional cerebral blood flow (rCBF). METHODS: We compared P-glycoprotein activity in mild-AD patients (n = 9) and cognitively normal, age-matched controls (n = 9) using PET with a labeled P-glycoprotein substrate, (11)C-verapamil, and (15)O-water to measure rCBF. BBB P-glycoprotein activity was expressed as the (11)C-verapamil radioactivity extraction ratio ((11)C-verapamil brain distributional clearance, K1/rCBF). RESULTS: Compared with controls, BBB P-glycoprotein activity was significantly lower in the parietotemporal, frontal, and posterior cingulate cortices and hippocampus of mild AD subjects. CONCLUSION: BBB P-glycoprotein activity in brain regions affected by AD is reduced and is independent of rCBF. This study improves on prior work by eliminating the confounding effect that reduced rCBF has on assessment of BBB P-glycoprotein activity and suggests that impaired P-glycoprotein activity may contribute to cerebral ß-amyloid accumulation in AD. P-glycoprotein induction or activation to increase cerebral ß-amyloid clearance could constitute a novel preventive or therapeutic strategy for AD.

Functional magnetic resonance imaging sequential-finger movement activation differentiating good and poor writers.

Good and poor fifth-grade writers differed, after controlling for multiple comparisons, in 42 brain regions on group maps and then individual brain analyses for functional magnetic resonance imaging (fMRI) contrast between tapping adjacent fingers sequentially and same finger repeatedly. Of these, 11 regions were correlated with both handwriting and spelling (transcription). Gender differences on the fMRI contrast, with girls more activated, occurred only in left superior parietal, which was correlated with handwriting and spelling. Significance of serial organization of fingers for handwriting and spelling is discussed.