Individual differences in the emotional reaction to shock determine whether hypoalgesia is observed.
OBJECTIVE
Our laboratory has shown that electrical shocks induce fear in human participants and subsequently inhibit pain on the hand receiving shocks. The present study examined whether pain modulation is bilateral, by testing pain on the hand contralateral to the one receiving shocks. We also evaluated whether individual differences in emotional response to the shocks influenced pain modulation.


METHODS
Following baseline tests, 61 participants were randomly assigned to one of two groups. In the shock group, participants received three surprising electrical shocks. In the control group, stimulating electrodes were removed from participants' fingers, and no shocks were presented. Both groups received two more pain threshold tests 2 and 8 minutes later.


METHODS
Similarly to the tail-flick test used in rodents, pain threshold was tested by measuring the latency of finger withdrawal to radiant heat. The following manipulation checks assessed the emotional state induced by shocks and the control procedure: Self-reported affect, skin conductance level (SCL), heart rate (HR), and blood pressure (BP).


RESULTS
Surprisingly, self-reported affect data indicate that some participants reacted to the shocks with humor and fear, while others reacted primarily with fear. Therefore, these groups were analyzed separately. Participants reacting with fear only exhibited hypoalgesia; however, participants reacting with mixed fear and humor showed no change in pain. This divergent effect was not mediated by arousal, because SCL, HR, and BP were similar in both shocked groups (fear only, fear + humor).


CONCLUSIONS
These data suggest that fear-induced hypoalgesia occurs bilaterally. However, humor experienced concurrent with fear appears to inhibit hypoalgesia. These findings may help explain individual differences in pain following traumatic events.
Rhudy
Jamie L
JL
Department of Psychology, University of Tulsa, Tulsa, Oklahoma 74104, USA. jamie_rhudy@utulsa.edu
Meagher
Mary W
MW
D000293:Adolescent; D000328:Adult; D000698:Analgesia / Q000523:psychology*; D004597:Electroshock / Q000523:psychology*; D004644:Emotions; D005239:Fear / Q000523:psychology; D005260:Female; D007839:Functional Laterality; D006801:Humans; D007206:Individuality; D008297:Male; D010146:Pain / Q000523:psychology*; D010147:Pain Measurement; D017288:Pain Threshold / Q000523:psychology; D012016:Reference Values; D014925:Wit and Humor as Topic / Q000523:psychology