Influence of stimulus intensity on the categories of single-unit responses recorded from olfactory bulb neurons in awake freely-breathing rabbits.

This study analyzes the influence of increasing odor intensity on the single-unit activity of olfactory bulb neurons recorded in awake freely-breathing rabbits. Five odorants were delivered at four concentrations over a range of 2 log units. Inspiration-and expiration-related firing activities were analyzed separately to categorize the odor-evoked responses into excitation, suppression and no response. Increasing the odor concentration caused more neurons to show excitatory responses during the inspiratory phase of the respiratory cycle and/or suppressive responses during the expiratory phase. The highest concentration of each odor also caused several units to give suppressive responses during inspiratory phases or excitatory responses during expiratory phases. However, increasing odor concentration caused few responses (less than 2%) to change from excitation to suppression or vice versa. How these results relate to those from studies performed in anaesthetized animals and the implications of the results for olfactory coding will be discussed.