Objective: To investigate the maturation of the auditory cortex by non-invasive recording of auditory evoked magnetic fields in human fetuses and newborns with the relatively novel and completely non-invasive technology of MEG. Methods: Serial recordings were performed every 2 weeks on 18 fetuses beginning from week 27 of gestational age until term with a follow-up recording on the newborn. Auditory stimulation consisted of tone bursts in an oddball design with standard tones and deviant tones. Results: In 52 of 63 fetal and in all of the neonatal recordings an auditory evoked magnetic field was obtained. A decrease in latency with increasing age of the subjects was observed in the combined analysis of fetuses and neonates. Conclusions: With advanced study using MEG, 83% of the measurements showed auditory evoked fields in fetuses that correspond with existing literature in electrophysiology in the past. These findings indicate that MEG is a technique that can be used to investigate maturation of the auditory cortex based on auditory evoked fields in fetuses and neonates. Significance: Maturational changes have been examined in the past. With the use of this novel technique, applied to a serial study, it is possible to trace the development of auditory responses in utero and newborns.
Norton JD, Eswaran H, Lowery CL, Wilson JD, Murphy P, and Preissl H
Journal Of Neuroscience Methods [J Neurosci Methods] 2004 Sep 30; Vol. 138 (1-2), pp. 157-64.
Acoustic Stimulation methods, Age Factors, Brain physiology, Computer Simulation, Confidence Intervals, Female, Gestational Age, Humans, Pregnancy, Reproducibility of Results, Signal Processing, Computer-Assisted, Time Factors, Brain radiation effects, Evoked Potentials, Auditory physiology, Fetus physiology, and Magnetoencephalography methods
Statistically valid detection of evoked responses from magnetoencephalographic (MEG) sensors is complicated by temporal autocorrelation. By decorrelating time series and transforming them toward normality, the discrete wavelet transform (DWT) allows the analyst to test for an association between stimulus and sensor time series with appropriate degrees of freedom. Eswaran et al. (Neurosci. Lett. 2002a;331:128-32) used a 151-channel fetal MEG system to obtain serial recordings from 10 pregnant subjects. There were 3-8 recordings per subject. In each recording session, the fetus was stimulated by 500Hz and 1KHz tones with a relative frequency of 80-20%, respectively. In this new analysis of the same data, the fetal MEG signals were compared to two different stimulus waveforms: the frequent tone and the Novel stimulus, defined as a change in pitch. WaveDetect was developed to determine whether there was a significant association between the stimuli and the MEG traces. This test is performed by taking the DWT of each series and then computing the Spearman correlation between the wavelet coefficients for an appropriate scale. A significant response (i.e., correlated stimulus-sensor pair) was detected from each patient. This result suggests that the combination of serial recordings and WaveDetect may ensure reliable detection of auditory evoked responses.