Functional hemispheric asymmetries in humans: electrophysiological evidence from preterm infants

In recent years, magnetic resonance imaging has allowed researchers to individuate the earlier morphological development of the right hemisphere compared with the left hemisphere during late-gestational development. Anatomical asymmetry, however, does not necessarily mean functional asymmetry, and whether the anatomical differences between hemispheres at this early age are paralleled by functional specialisations remains unknown. In this study, the presence of lateralised electrical brain activity related to both pitch detection and discrimination was investigated in 34 prematurely-born infants [24-34 gestational weeks (GWs)] all tested at the same post-conceptional age of 35 weeks. By means of a frequency-change oddball experimental paradigm, with 'standard' tones at 1000 Hz (P = 90%) and 'deviant' tones at 2000 Hz (P = 10%), we were able to record higher right event-related potential activity in the interval windows between 350 and 650 ms after stimulus onset. An explorative hierarchical cluster analysis confirmed the different distribution of the hemispheric asymmetry score in newborns < 30 weeks old. Here, we show electrophysiological evidence of the early functional right lateralisation for pitch processing (detection and discrimination) arising by 30 GWs, but not before, in preterm newborns despite the longer environmental sensorial experience of newborns < 30 GWs. Generally, these findings suggest that the earlier right structural maturation in foetal epochs seems to be paralleled by a right functional development.