A Beta2-Frequency (20-30 Hz) Oscillation in Nonsynaptic Networks of Somatosensory Cortex

Beta2 frequency (20-30 Hz) oscillations appear over somatosensory and motor cortices in vivo during motor preparation and can be coherent with muscle electrical activity. We describe a beta2 frequency oscillation occurring in vitro in networks of layer V pyramidal cells, the cells of origin of the corticospinal tract. This beta2 oscillation depends on gap junctional coupling, but it survives a cut through layer 4 and, hence, does not depend on apical dendritic electrogenesis. It also survives a blockade of a-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors or a blockade of$GABA_{A}$receptors that is sufficient to suppress gamma (30-70 Hz) oscillations in superficial cortical layers. The oscillation period is determined by the M type of K⁺ current.