Article
Exploration of electrode position to optimise the signal-to-noise ratio of the Auditory Steady State Response in infants
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Published: | May 31, 2005 |
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Outline
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Introduction
To identify EEG derivations that yield high signal to noise ratios of the Auditory Steady State Response (ASSR) in infants aged 0 to 5 months.
Materials and Methods
The ASSR was recorded simultaneously from ten EEG derivations in a monopolar montage in 20 sleeping infants. Stimuli were tones of 0.5 or 2 kHz which were 100% amplitude modulated (AM) and 20% frequency modulated, presented at 65 dB SPL for 4.4 minutes in either the right or the left ear. An AM of 90 Hz (left ear) or 94 Hz (right ear) was used. All 45 bipolar derivations were calculated from the 10 measured monopolar ones 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 set of derivations consisted of the left and right mastoid with Cz as common reference. This set improved SNRs compared to each of several conventional EEG derivations between 0-69% (500 Hz, left ear), 0-132% (500 Hz, right ear), 0-193% (2 kHz, left ear) and 0-105% (2kHz, 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 six months if the ASSR was recorded from the mastoids ipsilateral to the ear of stimulation referenced to Cz.