letters to nature brain ' s olfactory code

in the brain have long been investigated13. Recent studies in the insect antennal lobe suggest that precise temporal andlor spatial patterns of activity underlie the recognition and discrimination of different o d o ~ r s ~ ~ , and that these patterns may be strengthened by associative learning@' . It remains unknown, however, whether these activity patterns persist when odour intensity varies rapidly and unpredictably, as often occurs in nature10311. Here we show that with naturally intermittent odour stimulation, spike patterns recorded from moth antennal-lobe output neurons varied predictably with the fine-scale temporal dynamics and intensity of the odour. These data support the hypothesis that olfactory circuits compensate for contextual variations in the stimulus pattern with high temporal precision. The timing of output neuron activity is constantly modulated to reflect ongoing changes in stimulus intensity and dynamics that occur on a millisecond timescale. In order to examine the relationship between the fine-scale structure of a natural odour plume and the complex patterns of odour-evoked activity in the brain, we used a well-characterized olfactory subsystem in male moths that is devoted to processing infoimation about the female sex pher~mone""'~ First, an electroantennogram (BAG) was used to monitoi the spatiotemporal properties of a pheromone plume generated inside a laboratory wind tunnel (Fig la) Surprisingly, the structure of the odour