Cerebral Dynamics of SEPs to Non-Painful and Painful Cutaneous Electrical Stimulation of the Thenar and Hypothenar David M. Niddam*, Lars Arendt-Nielsen*, and Andrew C.N. Chen* Summary: Early, middle and late latency somatosensory evoked potentials (SEPs) elicited by cutaneous electrical stimulation (painful vs. non-painful) of right and left hands were recorded. The aims were to study (1) if lifelong use of dominant right hand would result in different SEP to- pographies compared to non-dominant left hand stimulation, (2) if painful and non-painful stimuli resulted in different SEP activation patterns for the different latency components and (3) if these results were consistent between two areas of the hand. Electrical stimuli were applied cutaneously above the thenar and hypothenar muscles of the left and right hand. A two-way repeated measures ANOVA was used to test the effects of laterality and in- tensity for a given peak amplitude and latency. Statistical results yielded no significant difference in peak amplitude for either thenar and hypothenar between the two hands. In contrast, a significant difference in amplitude was observed for 6 components for each stimulus location when the two in- tensities were compared. These components were found at early, middle and late latencies. No significant latency shift was observed between the two hands. Only the P30 component showed a significant latency shift for both locations with the painful condition having the shorter latency. Thus, life-long use of the dominant hand does not generate detectable changes in cortical evoked activity to sensory input from the skin above thenar and hypothenar muscles. Several SEP components across the time course (0-400 ms) showed increased amplitude when the stimulus was increased from non-painful to painful intensity. Key words: Pain; Cutaneous electrical stimulation; Thenar-hypothenar; Left-right hand; Somatosensory evoked potentials; Topographic maps. Introduction In the last two decades somatosensory evoked po- tentials (SEP) to electrical stimulation have been widely used to assess the underlying mechanisms of cortical processing. In contrast to other brain imaging techniques such as PET and fMRI, the recording of EPs gives infor- mation on a millisecond time scale, and thus gives the op- portunity to study the cortical areas involved in the early processing. In the recent years an increasing number of recording electrodes have been applied together with new dynamic topographical techniques to study SEPs. This has given further insight into which cortical areas are activated following both non-painful and painful stimulation. Most of these studies only examined the late components (Bromm and Chen 1995; Magerl et al. 1999; Treede et al. 1988; Valeriani et al. 1996), but rarely exam- ined the early activation to painful stimulation. Studies involving early (0-50 ms) and middle (50-100 ms) latency components have mainly been done by applying electri- cal stimulation to the median, sural or tibial nerves. In this time range intensity effects has been reported for the above mentioned nerves (Huttunen 1995; Dowman 1994; Tsuji et al. 1984). Still only a few topographical studies have systematically investigated the effects of non-painful and painful electrical stimulation in the full time interval from early to late latency (0-400 ms). The change of these early and the later components can now be used for examination of the cortical reorgani- sation. From studies in both primates (Kaas and Florence 1997) and humans (Cohen et al. 1998; Elbert and Flor 1999) it is known that the cerebral hemispheres are not static structures but develops and reorganises through- out life according to functionality e.g., as in corticomotor projection to the hand in a group of elite racquet players (Pearce et al. 2000) or before/after regional anesthesia (Birbaumer et al. 1997). Thus a difference in cerebral somatosensory and motor processing of non-dominant and dominant hands could be expected. However, no re- * Human Brain Mapping and Cortical Imaging Laboratory, Center for Sensory-Motor Interaction, Aalborg University, Aalborg, Denmark. Accepted for publication: September 11, 2000. This study was supported by the Danish National Research Foun- dation. Correspondence and reprint requests should be addressed to Prof. Andrew C.N. Chen, Human Brain Mapping and Cortical Imaging Lab- oratory, Center for Sensory Motor Interaction, Aalborg University, Fredrik Bajers Vej 7D-3, DK-9220, Denmark. Fax: +45 98 15 40 08 E-mail: ac@smi.auc.dk Copyright © 2000 Human Sciences Press, Inc. Brain Topography, Volume 13, Number 2, 2000 105