Brain resting state is disrupted in chronic back pain patients

Abstract

Recent brain functional magnetic resonance imaging (fMRI) studies have shown that chronic back pain (CBP) alters brain dynamics beyond the feeling of pain. In particular, the response of the brain default mode network (DMN) during an attention task was found abnormal. In the present work similar alterations are demonstrated for spontaneous resting patterns of fMRI brain activity over a population of CBP patients (n=12, 29-67 years old, mean=51.2). Results show abnormal correlations of three out of four highly connected sites of the DMN with bilateral insular cortex and regions in the middle frontal gyrus (p<0.05), in comparison with a control group of healthy subjects (n=20, 21-60 years old, mean=38.4). The alterations were confirmed by the calculation of triggered averages, which demonstrated increased coactivation of the DMN and the former regions. These findings demonstrate that CBP disrupts normal activity in the DMN even during the brain resting state, highlighting the impact of enduring pain over brain structure and function.

Figure 1

Procedure to extract hubs of the RSN. A. One of the eight RSNs obtained with PICA is selected (in this case, RSN4). B. BOLD signals are extracted from all voxels belonging to the RSN and linear correlations computed between each pair of voxels. C. Functional connectivity networks are constructed for each subject, choosing thresholds so that all networks have the same degree density δ. D. Normalized degree distributions are mapped into the cortex anatomy for all subjects and RSNs. E. Maps are averaged for different groups of subjects and seeds are defined by the regions with the greatest connectivity.

Figure 2

A. Position of the 27 seeds classified by RSN's membership. Note that some seeds belong to more than one RSN. B. Ranking of seeds according to their global normalized degree (gray line: average normalized degree distribution for group 1, formed by 12 healthy controls and δ = 0.05). Colour code of the line segments indicates RSN membership (if a seed belongs to more than one RSN the colour indicates the RSN in which the seed has the greatest degree).

Figure 3

A. Ratio of positive and negative correlated voxels for all 27 seeds. (*) Indicates significant differences (t-test, p<0.005). B. Spatial maps showing increased (left) and decreased (right) correlations with seeds in ORBmid, ANG.R and ANG.L in CBP (t-test, p<0.05 in red (left) and blue (right), p<0.001 in yellow (left) and purple (right).

Figure 4

BOLD signal averages triggered by spontaneous increases in the BOLD signal at ORBmid, ANG.R and ANG.L. (approx. 250 events) A. Triggered averages computed in the seeds and in the insular cortices (columns indicate the brain regions where the average is computed, and rows the regions where the events triggering the averaging occur). B. Similar analysis for two sites which do not exhibit broken correlation balance (PCUN.R and IPC). Asterisks indicate t-test significant differences: (*) for p<0.05 and (**) for p<0.005.