Preceding inhibition silences layer 6 neurons in auditory cortex

Neuron. 2010 Mar 11;65(5):706-17. doi: 10.1016/j.neuron.2010.02.021.

Abstract

A canonical feedforward circuit is proposed to underlie sensory cortical responses with balanced excitation and inhibition in layer 4 (L4). However, in another input layer, L6, sensory responses and the underlying synaptic circuits remain largely unclear. Here, cell-attached recordings in rat primary auditory cortex revealed that for the majority of L6 excitatory neurons, tonal stimuli did not drive spike responses, but suppressed spontaneous firings. Whole-cell recordings further revealed that the silencing resulted from tone-evoked strong inhibition arriving earlier than excitation. This pattern of inputs can be attributed to a parallel feedforward circuit with both excitatory and inhibitory inputs disynaptically relayed. In contrast, in the other neurons directly driven by thalamic input, stimuli evoked excitation preceding relatively weak inhibition, resulting in robust spike responses. Thus, the dichotomy of L6 response properties arises from two distinct patterns of excitatory-inhibitory interplay. The parallel circuit module generating preceding inhibition may provide a gating mechanism for conditional corticothalamic feedback.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acoustic Stimulation / methods
  • Animals
  • Auditory Cortex / cytology*
  • Drug Combinations
  • Electric Stimulation / methods
  • Electroencephalography
  • Evoked Potentials, Auditory / drug effects
  • Evoked Potentials, Auditory / physiology
  • Female
  • GABA Agonists / pharmacology
  • GABA Antagonists / pharmacology
  • Membrane Potentials / physiology
  • Models, Neurological
  • Morpholines / pharmacology
  • Muscimol / pharmacology
  • Nerve Net / drug effects
  • Nerve Net / physiology
  • Neural Inhibition / physiology*
  • Neurons / physiology*
  • Patch-Clamp Techniques / methods
  • Rats
  • Rats, Sprague-Dawley
  • Synaptic Transmission / drug effects

Substances

  • (+)-(S)-5,5-dimethylmorpholinyl-2-acetic acid
  • Drug Combinations
  • GABA Agonists
  • GABA Antagonists
  • Morpholines
  • Muscimol