Magnetically tethered flight assay and spatio-temporal measurement of odor plume tracking. (A) A hungry fly is tethered within a magnetic field that allows her to steer freely in the yaw plane. A wraparound LED display arena displays either a high contrast stationary grating pattern or moving features to "drag" the animal toward the odor nozzle. The nozzle delivers a smooth narrow odor plume which is drawn downward by an acrylic suction chamber. The fly's angular heading in the arena is tracked with IR video and software written in Matlab. (B) A miniature-photoionization detector (mini-PID) was used to make odor intensity measurements within a 9 mm2 space occupied by the fly. Odor intensity, in arbitrary units, is plotted in pseudo-color. Each point in the grid was sampled 11 different times below the plane of a fly in flight and the resulting data was smoothed using piecewise linear interpolation in Matlab. (C)The plume was pulsed with a solenoid valve system, and the temporal fidelity of the pulse train was verified with mini-PID measurements made at the location of the tethered fly.