Ethnic differences in the nociceptive flexion reflex (NFR).

A substantial body of literature suggests that the experience of both clinical and experimental pain differs among ethnic groups, with African Americans generally reporting greater sensitivity to chronic and experimentally induced pain when compared to non-Hispanic whites. However, no studies to date have examined nociceptive processes that may underlie these differences. The nociceptive flexion reflex (NFR) is based on the measurement of stimulus-induced spinal reflexes. Prior research suggests that the NFR threshold, or RIII response, is highly correlated with subjective pain thresholds. The current study evaluated responses to the nociceptive flexion reflex in healthy young adults from two different ethnic groups: African Americans (n=29) and non-Hispanic whites (n=28). Perceptual responses (e.g., pain ratings) as well as physiological reflex responses (i.e., biceps femoris EMG) were assessed. Significant ethnic group differences were observed for NFR reflex threshold, with African Americans producing a reflex at lower stimulation intensities relative to non-Hispanic whites. Interestingly, verbal pain ratings at NFR threshold were not significantly different between the groups, suggesting that the lower stimulation intensities required to elicit a reflex in African-American versus non-Hispanic white participants were nonetheless perceived as similar. Psychological Involvement, Positive and Negative Mood, and Rumination were correlated with NFR threshold in a pattern that was consistent across both ethnic groups. These results extend previous research on ethnic differences in self-report measures of pain by demonstrating group differences in a nociceptive muscle reflex.