Spatio‐temporal dynamics of oscillatory network activity in the neonatal mouse cerebral cortex

We used a 60‐channel microelectrode array to study in thick (600–1000 µm) somatosensory cortical slices from postnatal day (P)0–P3 mice the spatio‐temporal properties of early network oscillations. We recorded local non‐propagating as well as large‐scale propagating spontaneous oscillatory activity. Both types of activity patterns could never be observed in neocortical slices of conventional thickness (400 µm). Local non‐propagating spontaneous oscillations with an average peak frequency of 15.6 Hz, duration of 1.7 s and maximal amplitude of 66.8 µV were highly synchronized in a network of ∼200 µm in diameter. Spontaneous oscillations of lower frequency (10.4 Hz), longer duration (23.8 s) and larger amplitude (142.9 µV) propagated with 0.11 mm/s in the horizontal direction over at least 1 mm. These propagating oscillations were also synchronized in a columnar manner, but these waves synchronized the activity in a larger neuronal network of 300–400 µm in diameter. Both types of spontaneous network activity could be blocked by the gap junction antagonist carbenoxolone. Electrical stimulation of the subplate (SP) or bath application of the cholinergic agonist carbachol also elicited propagating network oscillations, emphasizing the role of the SP and the cholinergic system in the generation of early cortical network oscillations. Our data demonstrate that a sufficiently large network in thick neocortical slice preparations is capable of generating spontaneous and evoked network oscillations, which are highly synchronized via gap junctions in 200–400‐µm‐wide columns. These via synchronized oscillations coupled networks may represent a self‐organized functional template for the activity‐dependent formation of neocortical modules during the earliest stages of development.