![]() 2007 Lepousez and Lledo 2013 Nusser et al. OB gamma and insect gamma-like odor-evoked antennal lobe oscillations are functionally related to discrimination of overlapping odor input patterns ( Beshel et al. The gamma and beta rhythms strongly depend on behavioral context and odor quality (for a review, see Kay et al. The theta rhythm is coupled to respiratory and sniffing frequencies ( Rojas-Líbano et al. These oscillations are classified into three bands: theta (1–12 Hz), low (40–60 Hz) and high (60–100 Hz) gamma ( Kay 2003 Lepousez and Lledo 2013), and beta (15–30 Hz). Local field potential (LFP) oscillations in the mammalian olfactory bulb (OB) represent coordinated neural activity that is dynamically regulated during olfactory processing. Increased granule cell excitability, produced in many ways, releases stronger graded inhibition, which supports beta as a very stable state in disparate circumstances. In a computational model of the olfactory bulb, we find that changes in granule cell excitability can gate fast transitions from gamma to beta during odor sampling. Gamma (40–100 Hz) and beta (15–30 Hz) oscillations in mammalian olfactory bulbs represent differential involvement of higher order brain areas and different cognitive networks. Our model argues that Ca 2+ flow through VDCCs alone could sustain beta oscillations and that the switch between gamma and beta oscillations can be triggered by an increase in the excitability state of a subpopulation of GCs. When GC excitability is increased, the activation of NMDA receptors and other VDCCs is also increased, allowing the slow decay time constants of these channels to sustain beta-frequency oscillations. Results from our model suggest that when GC excitability is low, the graded inhibitory current mediated by NMDA channels and voltage-dependent Ca 2+ channels (VDCCs) is also low, allowing MC populations to fire in the gamma frequency range. ![]() We investigate the effect that GC excitability has on network oscillations in a computational model of the MC-GC dendrodendritic network with Ca 2+-dependent graded inhibition. Much of this centrifugal input targets inhibitory interneurons in the GC layer and regulates the excitability of GCs, which suggests a causal link between the emergence of beta oscillations and GC excitability. When cortical descending inputs to the OB are blocked, beta oscillations are extinguished whereas gamma oscillations become larger. Gamma (and possibly beta) oscillations arise from interactions in the dendrodendritic microcircuit between excitatory mitral cells (MCs) and inhibitory granule cells (GCs). Odors evoke gamma (40–100 Hz) and beta (20–30 Hz) oscillations in the local field potential (LFP) of the mammalian olfactory bulb (OB).
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