Voltage-dependent fast (20-40 Hz) oscillations in long-axoned neocortical neurons.

Fast (20-80 Hz) oscillations of cortical activity, occurring during an increased level of focused alertness or elicited by optimal sensory stimuli, have been described by recording field potentials and neuronal firing in various cortical areas. Despite the increasing interest in this topic, little is known about the cellular mechanisms of the fast (generally termed 40-Hz) rhythm. An in vitro study demonstrated that, in sparsely spiny interneurons of frontal cortex, the 40-Hz rhythm is generated by a voltage-dependent persistent Na+ current, with the involvement of a delayed rectifier. Here we report depolarization-dependent 40-Hz oscillations in cat's motor and association neocortical neurons with identified projections to contralateral homotopic cortical area and thalamus. Our data indicate that this fast rhythm may be synchronized through intracortical and corticothalamic linkages.