Chinese scientists uncover why pain gets worse at night

HEFEI, March 20 (Xinhua) -- Many people with chronic pain find their discomfort manageable during the day but unbearable at night, and a team from China has now uncovered the neural mechanism behind these daily fluctuations.

The study, led by Zhang Zhi of the University of Science and Technology of China in eastern Anhui province, was published on Friday in the journal Science.

While the circadian rhythm of pain is a known biological pattern -- typically weaker during activity and stronger at rest -- the underlying mechanism was unclear. The brain's master clock, the suprachiasmatic nucleus (SCN) in the hypothalamus, was known to regulate sleep and hormones, but its direct link to pain was missing.

Using advanced viral tracing technology, the team mapped a specific neural pathway in mice that connects the SCN to the spinal cord. The researchers found that neurons in this pathway are controlled by the SCN's daily rhythm.

Since mice are nocturnal, their activity cycle is opposite to that of humans. During the mice's rest period (daytime), the SCN was highly active, driving this circuit to amplify pain signals in the spinal cord. At night, when the mice were active, SCN activity dropped, naturally reducing the intensity of pain signals transmitted through the spinal cord.

"This discovery explains why pain sensitivity follows a daily rhythm," Zhang Zhi explained, adding that it also provides a new theoretical basis for improving clinical pain management by aligning treatment schedules with the body's natural biological clock. ■