A fundamental feature of somatosensory cortex (S1) is its capacity for plasticity with the development of chronic pain disorders. However, whether the perception of evoked and spontaneous pain related is associated with structural or functional S1 reorganization, and how they are related are still unclear.

Led by Prof. KONG Yazhuo and Prof. HU Li from the Institute of Psychology of the Chinese Academy of Sciences, researchers found that functional S1 reorganization in patients with postherpetic neuralgia (PHN) was associated with acute evoked as well as spontaneous pain, while the structural features were comparable between PHN patients and healthy controls.

PHN is defined as pain persisting for more than three months after the onset or healing of herpes zoster. PHN-related pain comprises spontaneous pain (e.g., sharp, burning, and aching) as well as dynamic mechanical allodynia.

In the current study, multi-modality magnetic resonance imaging and a stimulus-response paradigm were combined to examine whether S1 structural or functional reorganization occurs to intensity-locked laser stimuli in PHN patients compared to matched healthy controls.

In response to the laser stimulation on the left hand, PHN patients exhibited no lateralization and significantly higher levels of activation in ipsilateral S1 (left), compared to the healthy controls with significant activations focused in contralateral S1 (right).

Moreover, nociception encoded regions in PHN patients and healthy controls showed different cerebral patterns at S1 – bilateral inferior S1 (IS1) for PHN patients and contralateral superior S1 (SS1) for healthy controls, and not overlapped. Importantly, the contralateral SS1, which engaged during evoked pain in controls encoded spontaneous pain in patients, suggesting functional S1 reorganization in chronic pain.

Additionally, the resting state data showed weaker bilateral SS1 connectivity in the PHN patients compared to the healthy controls, and the weaker connectivity was negatively modulated by their spontaneous pain.

The results suggest that functional reorganization in S1 might play a key role in chronic pain related to PHN, and could be a potential treatment target in this patient group.

This work was published in Human Brain Mapping on June 25 and it was funded by the National Natural Science Foundation of China.