During sleep and quiet immobility brief high-frequency (~180 Hz) oscillations called "ripples" are observed in the hippocampus and are suggested to be important for memory consolidation. Very similar oscillations albeit twice or three-times as fast (400-600 Hz) have been observed in sensory cortices of various species including humans in response to brief peripheral stimulation. The network basis for either type of oscillation is as yet unresolved but hippocampus ripples have been suggested to be paced by tonically depolarized fast-spiking inhibitory interneurons. We recently discovered that 400 Hz "ripplets" can be elicited reliably in layer 4 of mouse somatosensory cortex brain slices by brief (1-5 ms) optogenetic stimulation of thalamocortical axons. Using dual whole-cell recordings we studied the underlying synaptic circuitry and concluded that unlike the prevailing models of hippocampus ripples ripplets result from anti-phasic highly synchronous spike volleys in inhibitory (fast-spiking) and excitatory neurons generating an ultrafast synchronous barrage of alternating excitatory and inhibitory synaptic currents in both cell types. The functional role of ripplets in the behaving animal (or human) is open for speculations.