EFFECT OF STRESS ON SOMATOSENSORY EVOKED POTENTIALS USHA PANJWANI, S. B. SINGH, K. HARINATH, DEEPAK K. YADAVAND W. SELVAMURTHY * Defence Institute of Physiology and Allied Sciences, Delhi, India SUMMARY The study aimed to evaluate the usefulness of somatosensory evoked potentials (SEPs) in studying the response to two types of experimentally induced stressors, the cold pressor test (CPT) and exercise. The subjects were 20 healthy normotensive males, 25±35 yr old. SEPs were recorded at baseline, immediately after CPT, in the recovery period after CPT and also immediately after exercise and in the recovery period after exercise. The CPT and exercise produced no signi®cant alteration in the absolute latencies, interpeak latency and amplitude of N 10 and N 20 components of SEPs. CPT and exercise produced changes in the systolic, diastolic and mean arterial pressure and the heart rate. It may be relevant to study the eect of stress on the later cortical components of the SEPs. Copyright # 1999 John Wiley & Sons, Ltd. KEY WORDS Ð SEPs; stress; CPT; exercise Stress is an integral part of our daily life. It may be physical, mental, social or emotional. Stress modulates the autonomic nervous system and central nervous system activities so that the body copes with the challenge, the normal response being one of sympathetic overactivity. 1 Somatosensory evoked potentials (SEPs) recorded from the scalp have proved to be a valuable tool for assessing the integrity of spinal and brainstem pathways and the initial activation of primary sensorimotor cortical regions. The test has been proved to be a valuable clinical and experimental tool. 2,3 A recent study 4 has shown a reduced sensory conduction during the cold pressor test (CPT), whereas a previous report 5 reported no signi®cant eect of CPT on motor conduction. There is also reported to be an increase in nerve conduction after exercise. 6 In the present study, we aimed to investigate the eect of two types of experimentally induced stresses, CPT and exercise, on sensory conduction. The potential usage of SEPs in the evaluation of the stress response was also studied. MATERIALS AND METHODS The subjects were 20 healthy, normotensive males between 25 and 35 years. The experimental details were outlined and informed consent was obtained from the subjects. Approval was obtained from the Ethics Committee of the Institute and th Code of Ethics of the World Medical Association (Declara- tion of Helsinki, 1964 and Declaration of Tokyo, 1975) was followed. The recordings were carried out in an air-conditioned laboratory with the subjects lying in the supine position. Short latency somatosensory evoked potentials were recorded from the median nerve on the Nicolet Compact IV Evoked Potential System. The recordings were carried out baseline, during CPT, immediately after exercise and in the recovery phases following CPT and exercise. The SEP recording of recovery phase was taken when the heart rate and BP returned to basal levels. The recording electrodes were silver±silver chloride disc type attached with conducting paste. Electrode impedance was kept below 7 kO. The recording montages were FPz±A l and FPz±C 4 (FPz:10±20 international system, A l connected to Erb's point, C 4 connected to C 4 0 (2 cm posterior to C 4 )). The stimulating electrode was placed over the left median nerve on the wrist and ®xed in place by a Velcro tape with the anode end towards the palm. CCC 0748±8386/99/010035±06$17.50 Received 10 December 1996 Copyright # 1999 John Wiley & Sons, Ltd. Accepted 3 February 1998 STRESS MEDICINE Stress med. 15, 35±40 (1999) * Correspondence to: Dr W. Selvamurthy, Defence Institute of Physiology and Allied Sciences, Lucknow Road, Timarpur, Delhi-110054, India. Tel: 91-11-2946526/2937275/2940567/ 2931081. Fax: 91-11-2932869. e-mail: root@drdipa.ren.nic.in.