The influence of acute anxiety on assessment of nociceptive flexion reflex thresholds in healthy young adults.

The nociceptive flexion reflex (NFR) is a polysynaptic withdrawal reflex that occurs in response to painful stimulation. In human studies, NFR responsiveness has been used as a direct measure of nociception as well as an indirect measure of supraspinal modulation of nociceptive transmission. Previous studies have suggested that anxiety may influence NFR responding, and therefore it has been recommended that anxiety be reduced by familiarizing participants with assessment methodology prior to formal NFR assessment. The present study was designed to assess the influence of anxiety on NFR threshold. Using a repeated measures design, 40 men and women completed an NFR threshold assessment twice within session one, and twice again during a second session conducted 24h later. Within each assessment session, state anxiety was measured at the beginning of the session and immediately following each NFR threshold assessment. Results indicated that although anxiety increased in response to NFR threshold assessment and was positively related to subjective pain reports, anxiety was not related to observed NFR threshold levels. These findings suggest that individual differences in anxiety do not significantly affect NFR threshold level determinations under standard testing conditions.