EEG derivations providing auditory steady-state responses with high signal-to-noise ratios in infants.

OBJECTIVE: To identify EEG derivations that yield high signal-to-noise ratios (SNRs) of the auditory steady-state response (ASSR) in infants aged 0 to 5 months. DESIGN: The ASSR was recorded simultaneously from 10 EEG derivations in a monopolar montage in 20 sleeping infants. Stimuli were tones of 0.5 or 2 kHz that were 100% amplitude modulated and 20% frequency modulated, presented at 65 dB SPL for 4.4 minutes in either the right or the left ear. An amplitude modulation frequency of 90 Hz (left ear) or 94 Hz (right ear) was used. From the 10 measured monopolar derivations, all 45 bipolar derivations were calculated mounting up to 55 EEG derivations. EEG derivations were selected in the preferred set if they had the largest SNRs within subjects and if they were obtained significantly more frequently across subjects than was expected by chance (Monte Carlo simulation and Wilcoxon signed ranks test). RESULTS: The preferred derivations are both mastoids ipsilateral to the stimulated ear with Cz as common reference. These derivations improved SNRs compared with each of several conventional EEG derivations (excluding the preferred derivations) between 16 and 69% (500 Hz, left ear), 9 and 132% (500 Hz, right ear), 31 and 193% (2 kHz, left ear), and 3 and 105% (2 kHz, right ear). In contrast to results reported earlier for adults, high SNRs were not found at the inion-Cz derivation in these infants. CONCLUSIONS: High SNRs were obtained in infants aged younger than 6 months if the ASSR was recorded from the mastoids ipsilateral to the ear of stimulation referenced to Cz.