Interhemispheric connectivity estimated from EEG time-correlation analysis in preterm infants with normal follow-up at age of five.

Brain connectivity is associated with axonal connections between brain structures. Our goal was to quantify the interhemispheric neuronal connectivity in healthy preterm infants by automated quantitative EEG time-correlation analysis. As with advancing postmenstrual age (PMA, gestational age  +  postnatal age) the neuronal connectivity between left and right hemisphere increases, we expect to observe changes in EEG time-correlation with age. Thirty-six appropriate-for-gestational age preterm infants (PMA between 27-37 weeks) and normal neurodevelopmental follow-up at 5 years of age were included. Of these, 22 infants underwent 3-8 repeated EEG recordings at weekly intervals. The reduced 10-20 EEG electrode system for newborns was used with five sets of bipolar channels: central-temporal, frontal polar-temporal, frontal polar-central, temporal-occipital and central-occipital. We performed EEG time-correlation analysis between homologous channels of the brain hemispheres to identify interhemispheric similarity in EEG signal shape. For each 8 s epoch of the EEG the time-correlation values and the corresponding lag times were calculated for homologous channels on both hemispheres. In all channels, the median correlation value decreased significantly (between  -40% and  -60% decrease) from 27 to 37 weeks PMA, for gestational maturation. For the postnatal maturation only the central-temporal channel showed a significantly decreasing trend. In contrast, the median lag time showed no uniform change with PMA. The decreasing median correlation values in all homologous channels indicate a decrease in similarity in signal shape with advancing PMA. This finding may reflect greater functional differentiation of cortical areas in the developing preterm brain and may be explained by the increase of complex neural networks with excitatory and inhibitory circuitries.