Sound frequency change detection in fetuses and newborns, a magnetoencephalographic study

The mismatch negativity (MMN) response to auditory stimuli has been successfully recorded in newborns thus demonstrating the discriminative cognitive ability. The aim of our study was to determine whether and when such an MMN response could be detected in the human fetus. The recordings of weak magnetic fields from the fetal brain were performed with the 151 channel MEG system called SARA (SQUID Array for Reproductive Assessment). Two tone bursts were presented in a sequence of a standard complex tone of 500 Hz intermixed with a deviant complex tone of 750 Hz in 12% of the stimuli. Sound intensity delivered over the maternal abdomen was 110 dB. The interstimulus interval (ISI) varied between 500 ms and 1100 ms. Fetal response, corresponding to sound frequency change detection, was calculated from the records where responses to standard and deviant tones were observed. A successful response was found in 60% of 25 fetal recordings. The MMN response with an average latency of 321 ms was observed in 48% of the fetal data. In 12% of the fetal data, a late component, referred to as the late discriminative negativity (LDN) response, was detected with an average latency of 458 ms. The same paradigm was applied in 5 newborns after birth. The capability for sound discrimination is a prerequisite for normal speech development. The investigation of sound discrimination and related cortical activity of the fetus can help to identify and determine the nature of deficits caused by central processes in the auditory system at very early stages.