High frequency broadband activity detected noninvasively in infants distinguishes wake from sleep states

High frequency broadband activity (HFB; 70-150 Hz) indexes local brain activity. It is predominantly studied using invasive measures due to signal drop off from skull attenuation. We hypothesized that HFB is detectable in infants noninvasively through fontanelles and thin skull that have not fully developed. We analyzed scalp electroencephalography (EEG) data during wake and sleep states in 19 channels from 18 infants (1-4 months, both sexes). At the group level, linear mixed-effects models revealed greater HFB power in wake versus sleep states in midline and central channels near fontanelles, as well as in occipital channels over thin skull. These differences were detected with 90% reliability using as few as 25 seconds of data per state in as few as 10 subjects. On the individual level, linear mixed-effects models revealed the same wake > sleep effect with a mean reliability of 60% when using at least 50 seconds of data per state. These findings establish that noninvasive HFB detection in infants is not only possible at sites where the skull has not fully developed, but sufficiently robust to enable systematic investigation of early cognitive development.