Dynamic tuning of human withdrawal reflex receptive fields during cognitive attention and distraction tasks

Objectives: The aim of the present study was to investigate supraspinal modulation of human lower limb reflex receptive fields (RRFs) on the plantar side of the foot during cognitive tasks either distracting the subjects or actively directing their attention to the electrical stimuli directed to the sole of the foot. Methods: Twelve healthy volunteers participated. Nociceptive withdrawal reflexes (NWRs) were recorded in the ankle flexor tibialis anterior. The RRF was acquired by randomized activation of ten stimulation sites on the sole of the foot. The RRF was assessed during baseline, distraction, and attention in randomized order. Distraction was induced by the Stroop test, while attention was induced by requiring the subjects to localize the site of the stimulation and thereby forcing them to focus on the sole of the foot. Results: The area of the RRF was significantly enlarged during the distraction task compared to baseline (P < 0.05), whereas the RRF area was significantly reduced during the attention task compared to baseline (P < 0.05). Conclusion: The size of the RRF area was modulated by the cognitive state demonstrating a link between the cognitive activity and the descending control on spinal withdrawal reflex pathways. (C) 2011 European Federation of International Association for the Study of Pain Chapters. Published by Elsevier Ltd. All rights reserved.