The effects of stimulus rates on the amplitude of median nerve somatosensory evoked potentials: the developmental change.

We examined the effects of stimulus rates on the somatosensory evoked potential (SEP) amplitudes following median nerve stimulation at the wrist in 42 children. We divided these subjects into five groups according to their age (0-6 months, 7-12 months, 1-3 years, 4-6 years and more than 7 years) and measured the peak-to-peak amplitude of every component (N9, P10, N11, P13/14, N18, N20, P23, N30) at stimulus rates of 1.0, 3.5 and 5.5 Hz. From N9 to N18, there was no significant change in amplitude nor latency with stimulus rate change in all groups. The amplitude attenuation was found at the N20 and N30 peaks in the young group (0 months to 3 years) and at P23 in all groups with an increasing stimulus rate. The attenuation rate of P23 amplitude was influenced by the age of subjects, being greater in younger groups and greatest in the youngest group (0-6 months). The differences of amplitude attenuation rate between this group and the rest were statistically significant. The results of this study indicate that the amplitudes of the cortical components of SEP in children are greatly influenced by the stimulus rate. Thus when we discuss the amplitude of cortical waves in childhood, we should also pay attention to the stimulus rates.