Median nerve somatosensory evoked potentials in medical students: Normative data


1 Department of Physiology, Dr. BR Ambedkar Medical College, KG Halli, Bangalore, India

2 Department of Physiology, Sri Devraj Urs Institute of Medical Sciences, Devaraj Urs Academy, Kolar, Karnataka, India


Background: The median nerve N20 component constitutes the initial response of the primary somatosensory cortex to somatosensory stimulation of the upper extremity. Knowledge of the underlying generators is important for basic understanding of the initial sequence of cortical activation.
Materials and Methods: In the present study, normative data of cortical evoked potentials in particular of N20 wave onset and peak latencies by median nerve stimulation in a group of 100 medical students aged between 18 and 30 years were documented and the effect of physiological variables were studied. Descriptive statistics and Student t-test were used to analyze the healthy subjects and to compare N20 latencies for handedness, respectively. Regression analysis was used to show association between average N20 latencies and physiological variables from which regression formulae were calculated to predict normative values of these parameters.
Results: The results of the study indicated that N20 onset and peak latency values are significantly affected by limb length at 95% confidence level. Height is showing as a significant factor affecting N20 onset latencies but it is probably because of high correlation of height with limb length. Age though on linear regression showed some significant correlation with N20 onset and peak latency, multiple regressions showed that it does not affect N20 onset and peak latencies in the presence of other variables. Handedness did not affect both N20 onset and peak latency values.
Conclusion: Physiological variables do affect the N20 latencies and these should be standardized before usage for research in basic sciences at all age groups.


1. Lagerlund TD. Volume conduction. In: Daube J, editor. Clinical neurophysiology. New York: Oxford University Press; 2002. p. 28-36.  Back to cited text no. 1
2. Li C, Houlden DA, Rowed DW. Somatosensory evoked potentials and neurological grades as predictors of outcome in acute spinal cord injury. J Neurosurg 1990;72:600-9.  Back to cited text no. 2
3. David RB. Child and adolescent Neurology. 2nd ed. Blackwell Publishing Ltd., Haryana: Replika Press; 2005.  Back to cited text no. 3
4. Legatt AD, Soliman E. Somatosensory evoked potentials: General Principles. In: Heilman KM, Lorenzo N, Lutsep HL, editors. eMedicine: Neurology. St. Petersburg: eMedicine Corporation; 2006.  Back to cited text no. 4
5. Misra UK, Kalitha J. History of clinical neurophysiology. In: 2nd ed. Delhi: Elsivier; 2008. p. 1-11.  Back to cited text no. 5
6. Aminoff MJ. Electrodiagnosis in clinical neurology. In: Illustrated. 5th ed. Newyork: Elsevier Churchill Livingstone; 2005.  Back to cited text no. 6
7. DeLisa JA, Gans BM, Walsh NE. Physical medicine and rehabilitation: Principles and practice. Vol. 2. 4th ed. Philadelphia: Lippincott Williams and Wilkins; 2004.  Back to cited text no. 7
8. Bercovici E, Pang E, Sharma R, Mohamed IS, Imai K, Fujimoto A, et al. Somatosensory-evoked fields on magnetoencephalography for epilepsy Infants younger than 4 years with total intravenous anesthesia. Clin Neurophysiol 2008;119:1328-34.  Back to cited text no. 8
9. Huisman UW, Posthuma J, Hooijer C, Visser SL, de Rijke W. Somatosensory evoked potentials in healthy volunteers and in patients with dementia. Clin Neurol Neurosurg 1985;87:11-6.  Back to cited text no. 9
10. Kimura J. Peripheral nerve diseases. In: Daube JR, Mauguiere F, editors. Handbook of clinical neurophysiology. Vol. 7. Amsterdam: Elsevier: 2006. p. 338.  Back to cited text no. 10
11. Sonoo M, Kobayashi M, Genba-Shimizu K, Mannen T, Shimizu T. Detailed analysis of the latencies of median nerve SEP components, 1: Selection of the best standard parameters and the establishment of the normal value. Electroencephalogr Clin Neurophysiol 1996;100: 319-31.  Back to cited text no. 11
12. Tanosaki M, Ozaki I, Shimamura H, Baba M, Matsunaga M. Effects of aging on central conduction in somatosensory evoked potentials: Evaluation of onset versus peak methods. Clin Neurophysiol 1999;110:2094-103.  Back to cited text no. 12
13. Lamba D, Montaldi L, Grosso L, Veneselli P, Giribaldi E, Gaia. Short latency evoked somatosensory potentials after stimulation of the median nerve in children: Normative data. J Clin Neurophysiol 2009;26:176-82.  Back to cited text no. 13
14. Jung P, Baumgärtner U, Bauermann T, Magerl W, Gawehn J, Stoeter P, et al. Asymmetry in the human primary somatosensory cortex and handedness. Neuroimage 2003;19:913-23.  Back to cited text no. 14
15. Vaney N, Gupta S, Aggarwal S, Tandon OP. Median nerve somatosensory evoked potentials: Correlation with physical parameters. Indian J Physiol Pharmacol 1996;40:175-9.  Back to cited text no. 15
16. Mervaala E, Pääkkönen A, Partanen JV. The influence of height, age and gender on the interpretation of median nerve SEPs. Electroencephalogr Clin Neurophysiol 1988;71:109-13.  Back to cited text no. 16
17. Chiappa KH. Evoked potentials in clinical medicine. 3 rd ed. In: Chiappa KH, editor. Philadelphia: Lippincott Raven; 1997. p. 752.  Back to cited text no. 17