Effects of active movement and mental movement simulation on somatosensory evoked potentials: A current density reconstruction approach

Both, movement of the stimulated hand, as well as its mental simulation, lead to an attenuation of the median nerve somatosensory evoked potentials (SEPs), an effect commonly termed as „gating“. We have analysed multi-channel EEG-data to investigate the influence of active movement and mentally simulated movement on median nerve SEP-components using the method of current density reconstruction. This approach provides increased spatial resolution capacity in case of restricted „a priori“ knowledge concerning the underlying cortical generators, compared to conventional methods of EEG-data analysis such as dipole source modeling or spline interpolation mapping. This seems to be especially important for the source localization of mid- and long-latency SEP-components, which are known to reflect spatially more distributed source activity than e.g. the generation of the primary cortical activity of the N20-potential. Besides the well-known attenuation of the frontal N30-potential within the precentral cortex contralateral to the stimulated hand during active movement, our data reveal an enhancement of mid-latency SEP-components in the secondary somatosensory cortex (SII) and the supplementary motor area (SMA) during both active movement and mental movement simulation. Additionally, we provide evidence for an early gating effect at around 50 ms after stimulus onset in bilateral SII-cortices. We suggest that this effect results from a direct and transcallosal inhibition of the primary sensorimotor cortex. Our findings support the view that a serial processing of sensory information occurs, including the central region, the SII-cortex and the SMA. Furthermore, our data confirm previous results that suggest the same areas are activated during mental movement simulation and the execution of real movements.