Massage-Related changes in cortical activity and cerebral oxygenation in healthy term infants: an exploratory EEG-fNIRS study with sex-specific observations

Abstract

[ENG]Background: Central nervous system development is a rapid and highly plastic process during the first years of life. Tactile stimuli have been shown to induce cortical changes, but potential sex-related differences remain unexplored. This study aimed to investigate sex-specific differences in cortical activity and cerebral oxygenation in response to tactile stimulation via body massage. Methods: Four healthy full-term infants (two females and two males), all aged 11 weeks, were included in this prospective exploratory study. Each infant received a standardized 5 min massage protocol. Cortical activity and cerebral oxygenation were assessed using an 8-channel electroencephalogram (EEG) and functional near-infrared spectroscopy (fNIRS) before, during, and after the intervention, with a 5 min pre-intervention resting period used as the baseline. Results: EEG analysis focused on a single spectral band (4 Hz–30 Hz). This range was selected to capture the main cortical oscillations in infants, including theta, alpha, and beta activity, while delta activity below 4 Hz was partially excluded to reduce movement and physiological artifacts. Standard infant EEG bands were considered when defining this range. Data shows for the female subject an average PSD of −6.726 (± −4.075), and for the male subject, −12.594 (± −10.741). Although babies are of the same gestational age, they exhibited distinct basal cortical activity, which prevented comparisons from being made. Nevertheless, massage induced similar activity patterns in all subjects with increased cortical electrical activity in the left parietal region relative to baseline. fNIRS data showed that comparable HbO concentration patterns between participants were observed only during the second minute of recording. Relative to baseline, pre-intervention HbO responses displayed an opposite distribution, and the effects of the intervention differed by sex. The female participant exhibited a slight reduction in activation in the right hemisphere accompanied by a modest increase in the most ventral region of the left hemisphere. Conversely, the male participant showed an inverse response pattern, characterized by a marked increase in right hemispheric activation and a pronounced decrease in the left hemisphere during the intervention period. Conclusions: These preliminary observations suggest the presence of early variations in cortical processing that warrant further investigation in larger samples, although they cannot be considered conclusive. While baseline response patterns differed between participants, both showed increased left parietal activity during tactile stimulation. The inversion of HbO responses between the pre-intervention and intervention phases points to potential sex-related differences in hemodynamic trajectories. Nevertheless, these results remain preliminary, and larger, well-powered studies are required to determine whether these patterns reflect stable, sex-dependent developmental changes.