40 Hz oscillations can be induced in brain slices by activation of metabotropic glutamate receptors, either on inhibitory neurons, or inhibitory neurons in combination with principal neurons. Oscillations can occur synchronously over distances of several mm, as they do in vivo, despite long expected axon conduction times. Cellular mechanisms include mutual inhibition between interneurons, and the ability of interneuron doublets to signal phase relations between oscillating pyramidal cells (as B. Ermentrout and N Kopell may elaborate further). It has recently been shown in vitro that 40 Hz oscillations induce synaptic plasticity, that in turn alters the properties of the oscillation. Our understanding of these oscillations allows an understanding also of the cellular mechanisms (at least in cortical structures) of 3 types of anesthetic agents: benzodiazepines (e.g. "Valium"), barbiturates, and opiates, all of which either slow the oscillation, abolish it, or prevent it from synchronizing over distance. There may really be a connection between these oscillations and consciousness.