Transient flattenings in the EEG of newborns--a benign variation

A report on 43 instances of transient flattening of the EEG in sleeping newborns occurring near the onset of state 1 is presented. The depression of EEG activity is variable and lasts about 1 min. It is followed usually by highly discontinuous activity (tracé discontinu) which fades after a variable time (less than 1.5 min in 75% of cases), into a normal state 1 pattern. The incidence was 24% in a mixed group of infants of 43 weeks CA and under. Bilateral events were twice as common as unilateral ones. Flattenings were only seen at or close to the onset of the first state 1 in a sleep episode. We suspect that the phenomenon reflects the unusual functioning of mechanisms underlying the normal process of change from the low voltage continuous EEG in behavioural state 2 (active or REM sleep) to the higher voltage so-called synchronized discontinuous pattern of state 1 (non-REM or quiet sleep). Flattenings have no clinical significance beyond their importance as a normal variation in the neonatal EEG, about whose existence electroencephalographers should be aware. Post-flattening bursting should not be misinterpreted as epileptic activity.