Fetal cortical activation to sound at 33 weeks of gestation: a functional MRI study.
Résumé
Hearing already functions before birth, but little is known about the neural basis of fetal life experiences. Recent imaging studies have validated the use of functional magnetic resonance imaging (fMRI) in pregnant women at 38-weeks of gestation. The aim of the present study was to examine fetal brain activation to sound, using fMRI at the beginning of the third trimester of pregnancy. 6 pregnant women between 28- and 34-weeks of gestation were scanned using a magnetic strength of 1.5 T, with an auditory stimulus applied to their abdomen. 3 fetuses with a gestational age of 33 weeks, showed significant activation to sound in the left temporal lobe, measured using a new data-driven approach (Independent Component Analysis for fMRI time series). Only 2 of these fetuses showed left temporal activation, when the standard voxel-wise analysis method was used (p=0.007; p=0.001). Moreover, motion parameters added as predictors of the General Linear Model confirmed that motion cannot account for the signal variance in the fetal temporal cortex (p=0.01). Comparison between the statistical maps obtained from MRI scans of the fetuses with those obtained from adults, made it possible to confirm our hypothesis, that there is brain activation in the primary auditory cortex in response to sound. Measurement of the fetal hemodynamic response revealed an average fMRI signal change of +3.5%. This study shows that it is possible to use fMRI to detect early fetal brain function, but also confirms that sound processing occurs beyond the reflexive sub-cortical level, at the beginning of the third trimester of pregnancy.