Title: Oscillations in the Olfactory Bulb Carry Information about Odorant History

2 While odorant evoked oscillations in the vertebrate olfactory bulb have been studied extensively, information about their possible cognitive role has been missing. Using voltage sensitive dye imaging we show that repeated odorant presentations with interstimulus intervals of 2-12 seconds had dramatic and diverse effects on the three oscillations that occur in the turtle olfactory bulb. Two of the oscillations are strikingly depressed in response to the second stimulation even of a new odorant was presented. The third oscillation is enhanced if the odorant is the same but suppressed if the odorant is new. The effects suggest that the oscillations carry information about odorant novelty and consistency. 3 Introduction E. D. Adrian (Adrian, 1942) discovered oscillations that appear in the mammalian vertebrate olfactory bulb during and after odorant presentations. Subsequently it has been shown that odorants evoke more or less complex oscillatory patterning across many animal species (e. relevance and function of the oscillations is not clear. In other sensory systems synchronous activity of neurons may be used by the brain as the mechanism underlying binding of different features of sensory information Thus far, there are no results in vertebrates that have directly linked the olfactory bulb oscillations to a specific cognitive role. While there is evidence that the oscillations have a role in the differentiation of similar odors in locusts (Stopfer et al. In earlier experiments we used optical imaging with voltage sensitive dyes to monitor the odor evoked oscillations in the turtle olfactory bulb (Lam et al., 2000; Lam et al., 2003). We found that odorants evoke a slow depolarization and three independent oscillations in the turtle bulb. The three oscillations, rostral, middle and caudal, differ in their amplitude, location, frequency, duration, and latency (e.g. Figure 1A). In contrast to the results in locusts and slugs, but similar to the result in moths, fish, rats and rabbits, the oscillations in the turtle appear to be independent of odor quality or concentration (over a substantial range of concentrations) (Lam et al., 2000, 2003). Here we describe dramatic alterations in the oscillatory pattern that occur on repeated odorant presentations. The changes to two of the oscillations are odorant independent; in contrast, the change observed in the third oscillation depends on whether the odorant in the two presentations is the same or different. Thus, oscillations may have more than one role during odorant processing in vertebrates; the middle oscillation could be …