Electroencephalographic recordings from the developing human brain are
characterized by spontaneous neuronal bursts, the most common of which is the delta brush.
Although similar events in animal models are known to occur in areas of immature cortex and drive
their development, their origin in humans has not yet been identified. Here, we use simultaneous
EEG-fMRI to localise the source of delta brush events in 10 preterm infants aged 32–36
postmenstrual weeks. The most frequent patterns were left and right posterior-temporal delta
brushes which were associated in the left hemisphere with ipsilateral BOLD activation in the insula
only; and in the right hemisphere in both the insular and temporal cortices. This direct measure of
neural and hemodynamic activity shows that the insula, one of the most densely connected hubs in
the developing cortex, is a major source of the transient bursting events that are critical for brain
maturation.