How Global Are Olfactory Bulb Oscillations?

Abstract

Previous studies in waking animals have shown that the frequency structure of olfactory bulb (OB) local field potential oscillations is very similar across the OB, but large low-impedance surface electrodes may have favored highly coherent events, averaging out local inhomogeneities. We tested the hypothesis that OB oscillations represent spatially homogeneous phenomena at all scales. We used pairs of concentric electrodes (200 μm outer shaft surrounding an inner 2-3 μm recording site) beginning on the dorsal OB at anterior and medial locations in urethane-anesthetized rats and measured local field potential responses at successive 200 μm depths before and during odor stimulation. Within locations (outer vs. inner lead on a single probe), on the time scale of 0.5 s, coherence in all frequency bands was significant, but on larger time scales (10 s), only respiratory (1-4 Hz) and beta (15-30 Hz) oscillations showed prominent peaks. Across locations, coherence in all frequency bands was significantly lower for both sizes of electrodes at all depths but the most superficial 600 μm. Near the pial surface, coherence across outer (larger) electrodes at different sites was equal to coherence across outer and inner (small) electrodes within a single site and larger than coherence across inner electrodes at different sites. Overall, the beta band showed the largest coherence across bulbar sites and electrodes. Therefore larger electrodes at the surface of the OB favor globally coherent events, and at all depths, coherence depends on the type of oscillation (beta or gamma) and duration of the analysis window.

Coherent olfactory bulb gamma oscillations arise from coupling independent columnar oscillators

“…These data underlie current hypotheses that the OB, in addition to processing the information content of primary sensory inputs, also transforms the metric of this sensory information from a rate-coded basis among primary olfactory sensory neurons (OSNs) into a sparser, spike timing-based representation at the output of the OB [17][18][19][20][21] , thereby gaining the attendant advantages of this coding scheme 1 . Implicit in these theories of timing-based computation in the OB, critically, is the principle that gamma oscillations are substantially coherent across the entire olfactory bulb 20,22,23 . However, the capacity for such broad coherence is challenged by the heterogeneity in activation levels among mitral cells that encodes odor identity and other limitations of the dynamical systems presently proposed to underlie OB oscillations.…”

Physical model of coherent potentials measured with different electrode recording site sizes

“…Bullock and McClune (1989) reported finding no difference in coherence when comparing electrode recording sites with 1-m diameters to those with 50-m diameters or when comparing those with 25-m diameters to those with 250-m diameters. Kay and Lazzara (2010) later compared coherence between electrodes of very different sizes (200-vs. 2-to 3-m diameters). They found that the much larger electrodes reported slightly more coherence, although the spectral power was the same between the different electrode sizes.…”

Pharmacological manipulation of olfactory bulb granule cell excitability modulates beta oscillations: Testing a model

“…Gamma oscillations are thought to be more spatially localized to individual cortical areas and even parts of these areas, while beta oscillations are thought to represent a coordinated oscillation supported by bidirectional connections between OB and PC (Martin et al, 2006; Kay et al, 2009; Kay and Lazzara, 2010). Curiously, we found that aPC beta power was not significantly reduced when OB beta was reduced by scopolamine, but aPC gamma was significantly reduced when ipsilateral OB gamma was suppressed by infusion of APV (Fig.…”