Respiratory-phase-related coding of olfactory information in the olfactory bulb of awake freely-breathing rabbits.

The "across-neuron pattern" theory of olfactory information coding states that odorants are represented by spatial patterns of activity produced across-neurons in the olfactory bulbs. The present study analyzes the different response patterns encoding olfactory information in both the inspiratory and expiratory phases of the respiratory cycles of awake freely-breathing rabbits. We recorded the single-unit responses of 31 neurons to 5 different odorants, 3 of which were repeatedly delivered 5 times each. These responses were characterized by the change in their mean firing activity during the inspiratory and expiratory phases of the respiratory cycles respectively. Their processing using principal component analyses revealed that both the inspiration- and the expiration-related across-neuron profiles of responses contained information appropriate to the specification of each odorant. It was therefore concluded that there was a dynamic representation of odorants in the olfactory bulb of awake freely-breathing animals. This alternate representation of odorants by two profiles and its physiological significance are discussed.