Sleep neurophysiology as a biological correlate of infant temperament

Temperament, characterized as individual differences in reactivity and self-regulation, influences our behavior in everyday situations. It is apparent as early as infancy and shaped by genetic and environmental factors. A neurophysiological marker of temperament has been quantified during the waking state; however, it remains unknown how these associations manifest in sleep. To address this gap, we assessed nighttime sleep in 29 6-month-old infants (Mage = 6.145 months, SD = 0.399, 48% males) using a portable high-density electroencephalography. Temperament was assessed using a parent-rated questionnaire, focusing on 2 scales: negative affectivity and orienting/regulatory capacity. The correlation analyses included: (i) frontal asymmetry and (ii) whole-brain, electrode-wise correlations with temperament. The predefined frontal asymmetry correlation revealed that increased left-hemispheric slow-wave activity (SWA) corresponded to higher orienting/regulatory capacity scores. The whole-brain correlation showed that higher theta power across an array of electrodes over the prefrontal regions was associated with decreased negative affectivity scores. Local sleep depth over frontal and temporal brain areas, as reflected by SWA asymmetry and theta power, serves as a marker of self-regulatory abilities and affective traits, which, in turn, reflect differences in temperament. Our findings reveal that sleep neurophysiology is a biological correlate of temperament during preverbal stages.