Altered small-world, functional brain networks in patients with lower back pain.

In this study, we aimed to investigate the functional network changes that occur in patients with lower back pain (LBP). We also investigated the link between LBP and the small-world properties of functional networks within the brain. Functional MRI (fMRI) was performed on 20 individuals with LBP and 17 age and gender-matched normal controls during the resting state. The severity of the pain in the individuals with LBP ranged from 5 to 8 on a 0-10 scale, with 0 indicating no pain. Network-based statistics were performed to investigate the differences between the brain networks of individuals with LBP and those of normal controls. Several small-world parameters of brain networks were calculated, including the clustering coefficient, characteristic path length, local efficiency, and global efficiency. These criteria reflect the overall network efficiency. The brain networks in the individuals with LBP due to herniation of a lumbar disc demonstrated a significantly longer characteristic path length as well as a lower clustering coefficient, global efficiency, and local efficiency compared to those in control subjects. We found that LBP patients tended to have unstable and inefficient brain networks when compared with healthy controls. In addition, LBP individuals showed significantly decreased functional connectivity in the anterior cingulate cortex, middle cingulate cortex, post cingulate cortex, inferior frontal gyrus, middle temporal gyrus, occipital gyrus, postcentral gyrus, precentral gyrus, supplementary motor area, thalamus, fusiform, caudate, and cerebellum. We believe that these regions may be involved in the pathophysiology of lower back pain.

A study on small-world brain functional networks altered by postherpetic neuralgia.

Understanding the effect of postherpetic neuralgia (PHN) pain on brain activity is important for clinical strategies. This is the first study, to our knowledge, to relate PHN pain to small-world properties of brain functional networks. Functional magnetic resonance imaging (fMRI) was used to construct functional brain networks of the subjects during the resting state. Sixteen patients with PHN pain and 16 (8 males, 8 females for both groups) age-matched controls were studied. The PHN patients exhibited decreased local efficiency along with non-significant changes of global efficiency in comparison with the healthy controls. Moreover, regional nodal efficiency was found to be significantly affected by PHN pain in the areas related to sense (postcentral gyrus, inferior parietal gyrus and thalamus), memory/affective processes (parahippocampal gyrus) and emotional activities (putamen). Significant correlation (p<0.05) was also found between the nodal efficiency of putamen and pain intensity in PHN patients. Our results suggest that PHN modulates the local efficiency, and the small-world properties of brain networks may have potentials to objectively evaluate pain information in clinic.

Quantitative cerebral blood flow mapping and functional connectivity of postherpetic neuralgia pain: a perfusion fMRI study.

This article investigates the effects of postherpetic neuralgia (PHN) on resting-state brain activity utilizing arterial spin labeling (ASL) techniques. Features of static and dynamic cerebral blood flow (CBF) were analyzed to reflect the specific brain response to PHN pain. Eleven consecutive patients suffering from PHN and 11 age- and gender-matched control subjects underwent perfusion functional magnetic resonance imaging brain scanning during the resting state. Group comparison was conducted to detect the regions with significant changes of CBF in PHN patients. Then we chose those regions that were highly correlated with the self-reported pain intensity as "seeds" to calculate the functional connectivity of both groups. Absolute CBF values of these regions were also compared across PHN patients and control subjects. Significant increases in CBF of the patient group were observed in left striatum, right thalamus, left primary somatosensory cortex (S1), left insula, left amygdala, left primary somatomotor cortex, and left inferior parietal lobule. Significant decreases in CBF were mainly located in the frontal cortex. Regional CBF in the left caudate, left insula, left S1, and right thalamus was highly correlated with the pain intensity, and further comparison showed that the regional CBF in these regions is significantly higher in PHN groups. Functional connectivity results demonstrated that the reward circuitry involved in striatum, prefrontal cortex, amygdala, and parahippocampal gyrus and the circuitry among striatum, thalamus, and insula were highly correlated with each element in PHN patients. In addition, noninvasive brain perfusion imaging at rest may provide novel insights into the central mechanisms underlying PHN pain.