Delayed maturation of auditory-evoked responses in growth-restricted fetuses revealed by magnetoencephalographic recordings.

OBJECTIVE: The purpose of this study was to investigate fetal brain development of growth-restricted fetuses with auditory evoked responses (AER) that were recorded by the noninvasive magnetoencephalographic technique. STUDY DESIGN: Serial fetal recordings that started at 27 weeks of gestation were conducted on a fetal magnetoencephalographic device that was especially designed for obstetric assessment. Fifteen normotrophic fetuses were compared with 14 hypotrophic fetuses. After birth, 10 of the hypotrophic fetuses were diagnosed with asymmetric growth restriction; 4 fetuses were classified as symmetrically small for gestational age. RESULTS: Fetal AER latencies in both groups showed an average developmental decrease of 12.74 msec/wk (P = .0035). Hypotrophic fetuses had longer age-adjusted latencies compared with normotrophic fetuses, with a difference of 73.5 msec (P = .034). The subgroup of symmetrically growth-restricted fetuses showed the longest latencies for age, with a difference from the normotrophic fetuses of 120.0 msec (P = .045). CONCLUSION: The results indicate that biomagnetically recorded AER can be used to monitor functional brain development in growth-restricted fetuses.

Neonatal and fetal response decrement of evoked responses: a MEG study.

OBJECTIVE: To investigate the response decrements of visual evoked responses (VER) in newborns and assess the applicability of this paradigm to fetuses in magnetoencephalographic (MEG) recordings. METHODS: Twelve newborns with no known risks or complications participated at chronological ages between 6 and 22days. They constituted the follow-up group to a prenatal study conducted on a sample of 25 fetuses whose gestational age (GA) varied between 29 and 37weeks at the time of recording. Trains of four light flashes with an interstimulus interval of 2s followed by 10s without stimulation were delivered to record VER. RESULTS: Nine of the 12 newborns responded to the stimulation and showed response decrements in amplitude from the first to the last light flash. Furthermore, the response latency increased significantly from the first to the last stimulus. The remaining three recordings were discontinued early. Even though the prenatal visual evoked response rate was only 29%, the fetuses exhibited a response decrement after the first stimulus. CONCLUSIONS: The amplitude of VERs can be used to elicit a response decrement in newborns and, with limitations, even in fetuses. This paradigm might be a useful tool for a direct non-invasive assessment of neonatal and prenatal brain development and CNS functioning. SIGNIFICANCE: The proposed method might be a first step towards an early detection of developmental deficits in newborns and fetuses.

Habituation of visual evoked responses in neonates and fetuses: a MEG study.

In this study we aimed to develop a habituation paradigm that allows the investigation of response decrement and response recovery and examine its applicability for measuring the habituation of the visually evoked responses (VERs) in neonatal and fetal magnetoencephalographic recordings. Two paradigms, one with a long and one with a short inter-train interval (ITI), were developed and tested in separate studies. Both paradigms consisted of a train of four light flashes; each train being followed by a 500Hz burst tone. Healthy pregnant women underwent two prenatal measurements and returned with their babies for a neonatal investigation. The amplitudes of the neonatal VERs in the long-ITI condition showed within-train response decrement. An increased response to the auditory dishabituator was found confirming response recovery. In the short-ITI condition, neonatal amplitude decrement could not be demonstrated while response recovery was present. In both ITI conditions, the response rate of the cortical responses was much lower in the fetuses than in the neonates. Fetal VERs in the long-ITI condition indicate amplitude decline from the first to the second flash with no further decrease. The long-ITI paradigm might be useful to investigate habituation of the VERs in neonates and fetuses, although the latter requires precaution.

Early development of brain responses to rapidly presented auditory stimulation: a magnetoencephalographic study.

BACKGROUND: The processing of rapidly presented stimuli has been shown to be a precursor for the perception of speech in infants, long before they learn to speak. However, the onset and early development of rapid temporal processing (RTP) skills is not yet well understood. The main goal of this study was to assess the development of RTP skills during the prenatal and early postnatal stages of life. METHODOLOGY: Tone pairs were presented in two difficulties (long and short) and event-related magnetic fields were recorded using MEG. Pregnant women (22) (gestational ages between 29 and 38 weeks') participated in the fetal study and 15 returned for a neonatal follow-up study between 2 and 38 days after delivery or 38 and 44 weeks gestational age (GA). RESULTS: In the postnatal follow-up study, a trend towards two peaks with increasing chronological and gestational age was observed in the longer tone pair. However, no such trend was evident in neonatal responses to the short tone pairs or in fetal recordings. CONCLUSIONS: Neonates showed a gradual trend to successful processing of the longer tone pair with increasing age. By 22 days of chronological age, the infants processed this tone pair successfully, as indicated by two-peak waveforms. Therefore, the first 3 weeks of life could be critical for the development of RTP. SIGNIFICANCE: This study is a first approach towards the assessment of early RTP development. The results provide promising indications for future studies, which might lead to an early detection of deficits in speech perception and therefore prevent further language impairments.