Imprecise visual feedback about hand location increases a classically conditioned pain expectancy effect

We tested the hypotheses that rendering sensory input about hand location imprecise increases a classically conditioned pain expectancy effect, increases generalization of the effect to novel locations and reduces extinction of the effect. Forty healthy volunteers performed movements with their right hand along predefined paths. Each path passed through two locations that were defined as either (i) the conditioned stimulus (CS+; paired with a painful unconditioned stimulus - UCS), and (ii) unpaired (CS-). During acquisition phase, participants watched their hand as they moved it. Participants were randomly allocated to an Imprecise group (IG), for whom visual feedback of the hand was offset 30-50mm from its true location, or a Precise group (PG), for whom vision was not disrupted. In the test phase, participants moved their hands to five locations – the CS+, CS- and three locations that lay between the two (‘Generalisation stimuli’). Our first hypothesis was reported – pain expectancy was greater at the CS+ location in the IG than in the PG (6.9 [SD=1.9] vs 5.4 [SD=2.5], p=0.02). Pain expectancies generalised to novel locations similarly in both groups and there was no difference in extinction between groups. Our primary hypothesis was supported but our subsequent hypotheses were not.

Perspective: We conditioned pain expectancy at a certain location of one hand, even though most participants were unaware of the contingency. Conditioned pain expectancy was greater when sensory information about location was less precise. This adds support to the possibility that associative learning may play a role in the progression of an acute pain episode to a more generalized pain disorder.