Odor representations in olfactory cortex: "sparse" coding, global inhibition, and oscillations

Neuron. 2009 Jun 25;62(6):850-61. doi: 10.1016/j.neuron.2009.05.022.


The properties of cortical circuits underlying central representations of sensory stimuli are poorly understood. Here we use in vivo cell-attached and whole-cell voltage-clamp recordings to reveal how excitatory and inhibitory synaptic input govern odor representations in rat primary olfactory (piriform) cortex. We show that odors evoke spiking activity that is sparse across the cortical population. We find that unbalanced synaptic excitation and inhibition underlie sparse activity: inhibition is widespread and broadly tuned, while excitation is less common and odor-specific. "Global" inhibition can be explained by local interneurons that receive ubiquitous and nonselective odor-evoked excitation. In the temporal domain, while respiration imposes a slow rhythm to olfactory cortical responses, odors evoke fast (15-30 Hz) oscillations in synaptic activity. Oscillatory excitation precedes inhibition, generating brief time windows for precise and temporally sparse spike output. Together, our results reveal that global inhibition and oscillations are major synaptic mechanisms shaping odor representations in olfactory cortex.

Publication types

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

MeSH terms

  • Action Potentials / drug effects
  • Action Potentials / physiology*
  • Animals
  • Animals, Newborn
  • Biological Clocks / drug effects
  • Biological Clocks / physiology*
  • Biophysics
  • Electric Stimulation
  • Excitatory Amino Acid Antagonists / pharmacology
  • In Vitro Techniques
  • Long-Term Potentiation / physiology
  • Nerve Net / physiology
  • Neural Inhibition / drug effects
  • Neural Inhibition / physiology*
  • Neurons / physiology*
  • Odorants*
  • Olfactory Pathways / cytology*
  • Patch-Clamp Techniques / methods
  • Quinoxalines / pharmacology
  • Rats
  • Rats, Sprague-Dawley
  • Synaptic Transmission / drug effects
  • Synaptic Transmission / physiology
  • Time Factors


  • Excitatory Amino Acid Antagonists
  • Quinoxalines
  • 2,3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline