Cortical Excitability during Fixations Drives Frequency-Specific Neural Activity in Children and Adults

Extensive previous research has examined how neuronal oscillations support basic cognitive processes, from early development into adulthood. However, the question of how these oscillations originate and are maintained remains relatively underexplored. Here, we examine how transient increases in cortical excitability that occur time-locked to the offsets of spontaneous eye movements associate with frequency-specific neural activity, and how these relationships change over development and between contexts (social vs non-social). We examine two datasets of combined EEG and eye-tracking data from 24-month-old children (N=114) and adults (N=108) while they watched stimuli that were either social (an actor singing nursery rhythms) or non-social (dynamic toys). EEG data was time-locked to the offsets of eye movements and analysed using a spectrum of methods designed to highlight the progression of various neural signals across time, frequency, and space (topography). Fixation-related potentials (FRPs) manifest as a differentiable combination of eye movement-related artifact and genuine neural activity. Child FRPs are slower and unfold over longer time periods, which manifests as differences in the frequency domain. Even after removing artifact, dipoles associated with fixation-related P1 and N170 components manifest as Theta activity over fronto-central areas, along with activity in other frequencies, in children but not adults. Data sections where no fixation-related potentials are present show strongly attenuated oscillatory activity. Our results show that a variety of previously documented developmental effects in the frequency domain may be better understood as fine-grained, movement-induced brain states.