| Examination of the functional roles of oscillatory activity in mammalian olfactory systems is necessary to understanding the processing of olfactory information. Oscillations in the theta (2-15 Hz) and gamma (35-115 Hz) frequency bands have been most studied; we know relatively little about oscillatory activity in the beta frequency band (15-40 Hz). Previous research has shown bursts of beta oscillations in response to novel presentations of putative predator odorants as well as non-predator odorants. We address this data in a meta-analysis and find a significant correlation between physical properties of the odorants and the beta oscillatory responses, indicating that beta oscillations in the olfactory system are not specific to predator-related odorants.; We present the results of three original experiments. In the first two, 18-36 odorants are delivered to both awake and anesthetized rats on cotton swabs for 12 presentations of ≤10 seconds. We find that odorants with theoretical vapor pressures in the 1-100 mmHg range are associated with significantly enhanced beta oscillations, particularly in the awake condition, indicating that odorant chemistry may be responsible for variance. Furthermore, these oscillations appear only after multiple presentations of the odorants. The relationship between the vapor pressure of the odorants and the beta oscillatory response is not linear, and we suggest that the trigeminal system, rather than the olfactory system, is responsible for coding of odorants with extremely high vapor pressures. In the third experiment, odorants are delivered to awake rats in the air of an enclosed chamber. The beta burst response is not significantly different between odorants in this condition, suggesting that the context of odor delivery is important for the generation of beta oscillatory bursts.; The question of the function of beta oscillations remains unanswered; however we discuss our results as they relate to studies showing beta oscillations in olfactory structures during odor learning tasks. We also discuss possible mechanisms for the generation of beta oscillations in the olfactory bulb and pyriform cortex. |
