Pain wind-up is the perceived increase in pain intensity over time when a given stimulus is delivered repeatedly above a critical rate. It is caused by repeated stimulation of group C peripheral nerve fibers, leading to progressively increasing electrical response in the corresponding spinal cord (posterior horn) neurons due to priming of the NMDA receptor based response. 
- Feng Xu; Tianjian Lu (29 May 2011). Introduction to Skin Biothermomechanics and Thermal Pain. Springer. p. 347. ISBN 978-3-642-13201-8. Retrieved 25 April 2012.
- Pitcher and Henry. (2000), Eur. J. Neurosci., 12 :2006-2020