During prenatal and early postnatal periods, the brain experiences rapid growth. Fetuses are vulnerable to prenatal distress and preterm birth, which can increase the risk of neurodevelopmental conditions. Identifying neural markers for early detection in at-risk individuals is crucial. Aperiodic neural activity could serve as a marker for neural maturation, yet knowledge is limited on how gestational duration shapes its trajectory over time. There is also a gap in research on prenatal stress effects in brain electrophysiology in toddlers.

We used functional neuroimaging to study age- and gestational duration-related neural activity changes in neonates and 3-year-olds, as well as the effects of maternal prenatal distress in 3-year-olds. In Study I, we used auditory event-related potentials (ERPs) of electroencephalogram (EEG) to explore links between maternal depressive symptoms and perception of emotionally charged auditory stimuli in toddlers. Study II investigated age- and prematurity-related changes in aperiodic activity in neonates, using functional magnetic resonance imaging (fMRI) blood-oxygen-level-dependent (BOLD) signal. Study III examined normal variation in gestational duration- and age-related effects on aperiodic and periodic activity of the EEG power spectra in neonates and toddlers.

Our results showed developmental changes in aperiodic activity, with steeper slopes of EEG power spectra related to longer gestational duration and higher BOLD baseline activity and steeper slopes related to greater postmenstrual age. Interestingly, these associations seemed to partially reverse after birth. Preterm neonates had flatter slopes and lower BOLD baseline activity compared to term-born neonates. Sex-specific differences were observed, with female neonates showing higher BOLD baseline activity but flatter slopes, and female toddlers exhibiting higher EEG beta center frequency values than males. Additionally, toddlers of mothers with higher prenatal depressive symptom scores showed weaker responses to happy sounds.

In conclusion, aperiodic activity reflects age-related changes in early life, likely indicating maturational changes in neurodevelopment, with sex-specific differences. This pattern may follow a reverse U-shaped curve from prenatal period through early life, with birth marking an apex point in the process. The results support previous findings that prenatal maternal depressive symptoms and gestational duration influence brain development, with effects observed up to 3 years of age.