No two roses smell exactly alike, but our brain accurately bundles these variations into a single percept 'rose'. We found that ensembles of rat olfactory bulb neurons decorrelate complex mixtures that vary by as little as a single missing component, whereas olfactory (piriform) cortical neural ensembles perform pattern completion in response to an absent component, essentially filling in the missing information and allowing perceptual stability. This piriform cortical ensemble activity predicts olfactory perception.