Amygdala lesions produce analgesia in a novel, ethologically relevant acute pain test

Acute pain tests using mechanical stimuli typically do not involve objects important in the evolutionary history of the subjects, and may fail to eval uate the contribution of biobehavioral defensive reactions to the total pai n response. Spines are common structural defenses that project plants and a nimals against predation. The present studies examined the reaction to cont act with such natural, mechanical pain stimuli in the laboratory rat, utili zing a floor board with protruding pins located in the middle of a novel al ley (the "fakir" test). Behavioral responses were characterized in 10-min t ests (Experiment 1). Subjects showed voluntary contact with the pins follow ed by patterns of avoidance and risk assessment (Stretch attend and stretch approach). Few subjects crossed the array of pins. The amygdala has been i mplicated in the perception of pain, particularly in stressful or fearful c ontexts. In Experiment 2, the fakir test was used to examine, concurrently, the effects of amygdala lesions on analgesiometric (frequency and duration of pins crossings) and anxiometric (risk assessment) measures. Large, bila teral, lesions of the amygdala significantly increased both the number of p in crossings and time spent on the pins without affecting the risk assessme nt measures. These findings suggest a possible dissociation between anxiety and pain perception with an important (nonaffective) role for the amygdala in the latter. (C) 1999 Elsevier Science Inc.