Waves and stimulus-modulated dynamics in an oscillating olfactory network.

The temporal dynamics of electrical activity in an olfactory organ, the procerebral lobe of the terrestrial mollusc Limax maximus, is studied. The lobe exhibits intrinsic oscillations in its field potential. Intracellular recordings show that the lobe contains two classes of neurons, both with activity phase-locked to the oscillation. Neurons in one class produce periodic bursts of spikes while those in the other class fire infrequently but receive strong, periodic inhibition whose onset coincides with the burst. The large-scale activity of these neurons is imaged in preparations stained with voltage-sensitive dyes. We observe waves of electrical activity that span the width of the lobe and travel its full length along a longitudinal axis. Simultaneous optical and intracellular recordings show that the form of the wave reflects the electrical activity of both classes of neurons. The application of natural odor stimuli causes the electrical activity along the lobe to transiently switch from the state with propagating waves to one with spatially uniform oscillations. The behavioral and computational relevance of this change in global timing is discussed.