The hippocampus has been shown to undergo significant changes in rodent models of neuropathic pain; however, the role of the hippocampus in human chronic pain and its contribution to pain chronification has remained unexplored. Here we examine hippocampal processing during a simple visual attention task. We used functional MRI to identify intrinsic and extrinsic hippocampal functional connectivity (synchronous neural activity) comparing sub-acute back pain (SBP, back pain 1-4 months) and chronic back pain (CBP, back pain >10 years) to control subjects (CON). Both groups showed more extensive hippocampal connectivity than CON. We then examined the evolution of hippocampal connectivity longitudinally in SBP patients who recovered (SBPr, back pain decreases >20% in one year) and those with persistent pain (SBPp). We found that SBPp and SBPr have distinct changes in hippocampal-cortical connectivity over one year; specifically, SBPp subjects showed large decreases in connectivity with medial prefrontal cortex (HG-mPFC). Furthermore, in SBP patients the strength of HG-mPFC reflected variations in back pain over the year. These relationships were replicated when examined in a different task performed by SBP patients (rating fluctuations of back pain), indicating that functional connectivity of the hippocampus changes robustly in sub-acute pain, and the nature of these changes depends on whether or not patients recover from SBP. The observed reorganization of processing within the hippocampus and between the hippocampus and the cortex seems to contribute to the transition from sub-acute to chronic pain, and may also underlie learning and emotional abnormalities associated with chronic pain.
- Transition to Chronic Pain
- Functional Connectivity
- chronic pain
- prefrontal cortex
- Copyright © 2013, Journal of Neurophysiology