Abstract
There is a growing interest in finding ways to summarize the local connectivity properties of the brain through single brain maps. Here we propose a method based on the conditional mutual information (CMI) in the frequency domain. CMI maps quantify the amount of non-redundant covariability between each site and all others in the rest of the brain, partialling out the joint variability due to gross physiological noise. Average maps from a sample of 45 healthy individuals scanned in the resting state show a clear and symmetric pattern of connectivity maxima in several regions of cortex, including prefrontal, orbitofrontal, lateral–parietal, and midline default mode network components; and in subcortical nuclei, including the amygdala, thalamus, and basal ganglia. Such cortical and subcortical hotspots of functional connectivity were more clearly evident at lower frequencies (0.02–0.1 Hz) than at higher frequencies (0.1–0.2 Hz) of endogenous oscillation. CMI mapping can also be easily applied to perform group analyses. This is exemplified by exploring effects of normal aging on CMI in a sample of healthy controls and by investigating correlations between CMI and positive psychotic symptom scores in a sample of 40 schizophrenic patients. Both the normative aging and schizophrenia studies reveal functional connectivity trends that converge with reported findings from other studies, thus giving further support to the validity of the proposed method.
Highlights
In recent years there has been a growing interest in finding ways to summarize connectivity properties of the brain through maps based on sets of functional magnetic resonance images
First we show average conditional mutual information (CMI) maps from a sample of healthy individuals and, later, we evaluate possible patterns in CMI related to age in the healthy brain and related to clinical symptoms in a sample of patients with schizophrenia
We propose an alternative way of calculating maps of net levels of connectivity in the brain based on resting-state functional magnetic resonance images (fMRI) images
Summary
In recent years there has been a growing interest in finding ways to summarize connectivity properties of the brain through maps based on sets of functional magnetic resonance images (fMRI) These maps may use different measures of connectivity and have been named differently (e.g., maps of cortical hubs, Buckner et al, 2009; global brain connectivity maps, Cole et al, 2010; overall brain connectivity maps, Salvador et al, 2010) they aim at describing the general levels of connectivity between each site of the brain and the remaining brain. This, in turn, may lead to spurious covariances in areas of the brain like those located near prominent vascular structures
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