The somatosensory evoked potentials of normal infants: influence of filter bandpass, arousal state and number of stimuli.

Median nerve somatosensory evoked potentials (SEPs) were investigated in 35 normal newborns aged 0-5 days. During stimulation at a regular frequency of 0.5/s, potentials deriving from cervical (CS2-Fz) or scalp (C3'-Fz) level were recorded with five different bandpasses (1-100 to 100-5,000 Hz (-6 dB/oct], with a variable number of stimuli (25-350) and in different arousal states: awake or in irregular sleep (non-quiet), or in regular sleep (quiet). The 1-100 Hz filter introduced a slight distorsion of the N13 and N19 (1) and (2) potentials but a better signal-to-noise ratio compared with the other filter settings. A 20-5,000 Hz bandpass resulted in an inacceptable distorsion of the N19 (1) and (2) peak. For the 100-5,000 Hz bandpass an almost complete suppression of the cortical components was obtained. With a 1-100 Hz bandpass a N13 and a N19 potential could be recorded in all infants; in 75% of them a bilobed N19 peak was present. In the quiet state (n = 13) either a bilobed N19 peak was observed with prolonged N19 (1) and (2) peak latencies compared with the non-quiet state or a large unilobed N19 wave. An increase in the number of stimuli from 25 to 100 resulted in a decrease of 33% in the amplitude of the N19(1) peak. We advocate to record SEPs in the neonatal period with a filter bandpass of 1-100 Hz and with a low number of stimuli (25-50), with attention for the arousal state of the infant.