The Relationship between Structural and Functional Brain Changes and Altered Emotion and Cognition in Chronic Low Back Pain: A Systematic Review of MRI and fMRI Studies

OBJECTIVES:: Chronic low back pain (CLBP) is a major health issue, yet its underlying mechanisms remain unknown. Studies have demonstrated the importance of emotion and cognition in chronic pain, however, the relevant brain physiology in magnetic resonance imaging (MRI) studies are unclear in CLBP populations. Therefore, this review aimed to identify MRI brain changes and examine their potential relationship with emotional and cognitive processes in CLBP. METHOD:: A systematic search was conducted in 5 databases. Studies that recruited adult, chronic low back pain populations, and used brain MRI protocols were included. RESULTS:: Fifty-five studies met the inclusion criteria. Of the structural MRI studies, 10 of 15 studies found decreased gray matter and 7 of 8 studies found white matter changes in CLBP groups compared to controls. Fourteen resting-state functional MRI (fMRI) studies all reported differences between CLBP and control groups in the default mode network. Interestingly, only 3 of 10 fMRI studies observed significant differences during noxious stimulation between CLBP and control groups, while 13 of 16 studies observed significant brain activation differences in CLBP groups during various external tasks. Finally, there were 3 studies that observed a degree of recovery in functional connectivity following intervention. DISCUSSION:: The brain changes in CLBP groups were mainly observed in areas and networks important in emotion and cognition, rather than those typically associated with nociception. This supports the understanding that emotional and cognitive processes may be the core contributor to the CLBP experience, however, future studies need to explore these processes further.