Evaluation of the functional state of the somato-motor system using SEP and interfering stimuli

The analysis of median nerve stimulated SEPs recorded during interfering stimuli like hand movements, provides a promising tool to illuminate the functional state of the somato-motor system. Prior studies in general observed altered amplitudes of frontal (N30) and/or parietal (P27) peaks caused by interfering stimuli, demonstrating functional changes of the somato-motor system. We performed a study to evaluate whether different interfering stimuli cause different patterns of SEP alterations. SEPs were recorded with 64-channels and analysed using source analysis, global field power and mapping. Interfering stimuli were: mental complex finger movements, acted simple and acted complex finger movements, explorative finger movements and brushing of fingers I to III. Statistical evaluation revealed: 1) No difference between median nerve SEPs at rest and during mental finger movements. 2) Different patterns of maps computed at maxima of global field power between 25 and 35 ms post stimulus clearly distinguished between the 3 types of interfering stimuli, finger movements, explorative movements and pure sensory interfering stimulation in 8 out of 10 subjects. Hence, the analysis demonstrated different functional states of the somato-motor system to motor, pure sensory and both motor and sensory inputs.