Granule cell excitability regulates gamma and beta oscillations in a model of the olfactory bulb dendrodendritic microcircuit

J Neurophysiol. 2016 Aug 1;116(2):522-39. doi: 10.1152/jn.00988.2015. Epub 2016 Apr 27.


Odors evoke gamma (40-100 Hz) and beta (20-30 Hz) oscillations in the local field potential (LFP) of the mammalian olfactory bulb (OB). Gamma (and possibly beta) oscillations arise from interactions in the dendrodendritic microcircuit between excitatory mitral cells (MCs) and inhibitory granule cells (GCs). When cortical descending inputs to the OB are blocked, beta oscillations are extinguished whereas gamma oscillations become larger. 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. 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. 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. 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. 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.

Keywords: beta oscillation; excitability; gamma oscillation; granule cell; olfactory bulb.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Action Potentials / physiology
  • Animals
  • Beta Rhythm / physiology*
  • Biophysical Phenomena / drug effects
  • Biophysical Phenomena / physiology
  • Calcium / metabolism
  • Calcium Channels / metabolism
  • Computer Simulation
  • Dendrites / physiology
  • Electric Stimulation
  • Gamma Rhythm / physiology*
  • Inhibitory Postsynaptic Potentials
  • Interneurons / physiology*
  • Mice
  • Models, Neurological*
  • Nerve Net / physiology*
  • Neural Inhibition / physiology
  • Olfactory Bulb / cytology*
  • Receptors, N-Methyl-D-Aspartate / metabolism
  • Wakefulness
  • gamma-Aminobutyric Acid / pharmacology


  • Calcium Channels
  • Receptors, N-Methyl-D-Aspartate
  • gamma-Aminobutyric Acid
  • Calcium