What can evolutionary theory tell us about chronic pain? Amanda C de C Williams University College London, UK

Injury-related behavior Acute injury - escape danger & find safety - care for wound - rest injured part - conserve energy - be alert to further threat As healing proceeds - return to normal activities - start to use injured part - avoid circumstances associated with injury.

Sensitization Sensitization includes - increased nervous system sensitivity to tactile, chemical, mechanical & thermal stimuli - arousal - vigilance to threat All facilitate a rapid response to potential threat or injury

The advantage of sensitization Crook, Dickson, Hanlon & Walters, Current Biology 2014;24:1121-5 Nociceptive sensitization reduces predation risk Sensitization of defensive responses after injury suggests “powerful evolutionary selection pressures”. Nociceptive sensitization following injury in squid changed their behavior such that they were less predated. Price & Dussor, Current Biology 2014;24:R384 Evolution: the advantage of ‘maladaptive’ pain plasticity ““These findings have profound implications for pain neuroscientists and clinicians and, we will argue, for neurobiology in general.”

Implications Pain sets priorities for survival So: how much pain is optimal in a particular situation? To answer, we need: ecologically valid pain stimuli and pain responses in experimental work awareness of environmental and social context in experimental work evolutionary models of cognitive, emotional and social processes in pain