Improved neuromagnetic detection of fetal and neonatal auditory evoked responses

OBJECTIVE To assess the quality of fetal and neonatal auditory evoked responses (fAERs and nAERs) obtainable with a low-noise, high-channel count SQUID gradiometer in a well-shielded environment. METHODS Measurement of long-latency fAERs was attempted in 19 normal fetuses in 28 sessions at 29-40 weeks' gestation, using a 37-channel SQUID gradiometer. Postnatal measurement was attempted in 16 neonates in 25 sessions at age 2-6 weeks. RESULTS Signals of amplitude 8 fT or greater were detected in 15 of 28 fetal measurement sessions, yielding a higher success rate (54%) than in a previous study of ours. Signals of amplitude greater than 25 fT were detected in 23 of 25 (92%) of neonatal measurement sessions. The spatial and temporal characteristics of the signals were studied in greater detail. Dipole patterns consistent with a source in the auditory cortex were observable in nearly all neonates and in many fetuses. The dominant component of the nAER was compatible with the P250 seen in neonatal EEG recordings; however, the largest component of the fAERs had longer latency and in many subjects had opposite polarity. CONCLUSION A higher success rate, earlier detection, and improved characterization of signal morphology and topography were demonstrated for fAER recordings.