Disrupted correlation between low frequency power and connectivity strength of resting state brain networks in schizophrenia

Abstract

Altered brain connectivity has emerged as a central feature of schizophrenia. Low frequency oscillations and connectivity strength (CS) of resting state brain networks are altered in patients with schizophrenia (SZs). However, the relationship between these two measures has not yet been studied. Such work may be helpful in understanding the so-called "rich club" organization (i.e. high-CS nodes are more densely connected among themselves than are nodes of a lower CS in the human brain) in healthy controls (HCs) and SZs. Here we present a study of HCs and SZs examining low frequency oscillations and CS by first decomposing resting state fMRI (R-fMRI) data into independent components (ICs) using group independent component analysis (ICA) and computing the low frequency power ratio (LFPR) of each ICA time course. Weighted brain graphs consisting of ICs were built based on correlations between ICA time courses. Positive CS and negative CS of each node in the brain graphs were then examined. The correlations between LFPR and CSs as well as "rich club" coefficients of group mean brain graphs were assessed. Results demonstrate that the LFPR of some ICs were lower in SZs compared to HCs. In addition, LFPR was correlated with positive CS in HCs, but to a lesser extent in SZs. HCs showed higher normalized rich club parameter than SZs. The findings provide new insight into disordered intrinsic brain graphs in schizophrenia.

Figure 1

Spatial maps (z-score maps) of the 53 brain components identified by group ICA. Each component is shown in one column in axial, sagittal, and coronal views. ICs are indexed based on the sequence of output from GIFT. L: left; R: right.

Figure 2

Structure of the mean correlation matrix in each group. Nodes are indexed the same as Figure 1.

Figure 3

Group mean values of low frequency power ratio (LFPR, up side) and positive connectivity strength (CS, down side) for each IC. Height of the bar indicates the mean value of the relative measurement for the two groups and the color of the bar indicates the group. ICs are indexed (from left to right) same to Figure 1. Star indicates that IC (IC3 IC12 IC13 IC15 IC23 IC28 IC31 IC35 IC39 IC40) show significant group difference in LFPR.

Figure 4

Scatter plots with trend lines showing group mean positive connectivity strength (CS) as a function of group mean low frequency power ratio (LFPR) in HCs and SZs. Each dot denotes a brain component. Pearson correlation coefficient for HCs (r = 0.367, P = 0.007), for SZs (r = 0.213, P = 0.126).

Figure 5

Schematic weighted graphs showing the relationship between low frequency power ratio (LFPR) and positive connectivity strength (CS) plotted based on group mean values. Each node is a brain component. Color of a single line indicates the weight (correlation value) of that connection; size of the nodes indicates LFPR; color of nodes indicates positive CS.

Figure 6

Normalized rich club coefficient (Φ_norm) as a function of n (top n nodes with high positive CS) for the group mean weighted graphs. HCs showing higher Φ_norm over the range 3 – 50 (HCs:1.128 ± 0.033; SZs: 1.068 ± 0.071; two sample t-test: P < 1.0 × 10⁻⁶, df = 94).