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We previously showed that in a two-alternative choice (2AC) task, olfactory bulb (OB) gamma oscillations (∼70 Hz in rats) were enhanced during discrimination of structurally similar odorants (fine discrimination) versus discrimination of dissimilar odorants (coarse discrimination). In other studies (mostly employing go/no-go tasks) in multiple labs, beta oscillations (15–35 Hz) dominate the local field potential (LFP) signal in olfactory areas during odor sampling. Here we analyzed the beta frequency band power and pairwise coherence in the 2AC task. We show that in a task dominated by gamma in the OB, beta oscillations are also present in three interconnected olfactory areas (OB and anterior and posterior pyriform cortex). Only the beta band showed consistently elevated coherence during odor sniffing across all odor pairs, classes (alcohols and ketones), and discrimination types (fine and coarse), with stronger effects in first than in final criterion sessions (>70% correct). In the first sessions for fine discrimination odor pairs, beta power for incorrect trials was the same as that for correct trials for the other odor in the pair. This pattern was not repeated in coarse discrimination, in which beta power was elevated for correct relative to incorrect trials. This difference between fine and coarse odor discriminations may relate to different behavioral strategies for learning to differentiate similar versus dissimilar odors. Phase analysis showed that the OB led both pyriform areas in the beta frequency band during odor sniffing. We conclude that the beta band may be the means by which information is transmitted from the OB to higher order areas, even though task specifics modify dominance of one frequency band over another within the OB.

Several studies have shown that memory consolidation relies partly on interactions between sensory and limbic areas. The functional loop formed by the olfactory system and the hippocampus represents an experimentally tractable model that can provide insight into this question. It had been shown previously that odor-learning associated beta band oscillations (15–30 Hz) of the local field potential in the rat olfactory system are enhanced with criterion performance, but it was unknown if these involve networks beyond the olfactory system. We recorded local field potentials from the olfactory bulb (OB) and dorsal and ventral hippocampus during acquisition of odor discriminations in a go/no-go task. These regions showed increased beta oscillation power during odor sampling, accompanied by a coherence increase in this frequency band between the OB and both hippocampal subfields. This coherence between the OB and the hippocampus increased with the onset of the first rule transfer to a new odor set and remained high for all learning phases and subsequent odor sets. However, coherence between the two hippocampal fields reset to baseline levels with each new odor set and increased again with criterion performance. These data support hippocampal involvement in the network underlying odor-discrimination learning and also suggest that cooperation between the dorsal and ventral hippocampus varies with learning progress. Oscillatory activity in the beta range may thus provide a mechanism by which these areas are linked during memory consolidation, similar to proposed roles of beta oscillations in other systems with long-range connections.