Our brain connections become more sparse and sharp with aging.

I have the clear feeling that my 68-year old brain is more rye-crisp and sharp, less likely to experience rich emotional immersions in a passing moment, than my 28-year old brain was. I wonder if part of the explanation for this is suggested by work of Dosenbach et al., who recently have developed an index of resting-state functional connectivity (how tightly neuronal activities in distinct brain regions are correlated) from several three different data sets based on fMRI scans of 150 to 200 individuals from ages 6 to 35 years old. Networks become more sparse and sharp with brain maturation, as long-range connections increase while short-range connections decrease. Here is their abstract and a summary figure from the paper (I don't understand the statistics, but do give definitions of the abbreviations):

Group functional connectivity magnetic resonance imaging (fcMRI) studies have documented reliable changes in human functional brain maturity over development. Here we show that support vector machine-based multivariate pattern analysis extracts sufficient information from fcMRI data to make accurate predictions about individuals’ brain maturity across development. The use of only 5 minutes of resting-state fcMRI data from 238 scans of typically developing volunteers (ages 7 to 30 years) allowed prediction of individual brain maturity as a functional connectivity maturation index. The resultant functional maturation curve accounted for 55% of the sample variance and followed a nonlinear asymptotic growth curve shape. The greatest relative contribution to predicting individual brain maturity was made by the weakening of short-range functional connections between the adult brain’s major functional networks.

Figure (click to enlarge): fcMVPA (functional connectivity multivariate pattern analysis) connection and region weights. The functional connections driving the SVR (support vector machines regression) brain maturity predictor are displayed on a surface rendering of the brain. The thicknesses of the 156 consensus functional connections scale with their weights. Connections positively correlated with age are shown in orange, whereas connections negatively correlated with age are shown in light green. Also displayed are the 160 ROIs (regions of interest) scaled by their weights (1/2 sum of the weights of all the connections to and from that ROI). The ROIs are color-coded according to the adult rs-fcMRI (resting state functional connectivity MRI networks) (cingulo-opercular, black; frontoparietal, yellow; default, red; sensorimotor, cyan; occipital, green; and cerebellum, dark blue).