Anatomical and Functional Organization of Inhibitory Circuits in the Songbird Auditory Forebrain

Abstract

Recent studies on the anatomical and functional organization of GABAergic networks in central auditory circuits of the zebra finch have highlighted the strong impact of inhibitory mechanisms on both the central encoding and processing of acoustic information in a vocal learning species. Most of this work has focused on the caudomedial nidopallium (NCM), a forebrain area postulated to be the songbird analogue of the mammalian auditory association cortex. NCM houses neurons with selective responses to conspecific songs and is a site thought to house auditory memories required for vocal learning and, likely, individual identification. Here we review our recent work on the anatomical distribution of GABAergic cells in NCM, their engagement in response to song and the roles for inhibitory transmission in the physiology of NCM at rest and during the processing of natural communication signals. GABAergic cells are highly abundant in the songbird auditory forebrain and account for nearly half of the overall neuronal population in NCM with a large fraction of these neurons activated by song in freely-behaving animals. GABAergic synapses provide considerable local, tonic inhibition to NCM neurons at rest and, during sound processing, may contain the spread of excitation away from un-activated or quiescent parts of the network. Finally, we review our work showing that GABA A -mediated inhibition directly regulates the temporal organization of song-driven responses in awake songbirds, and appears to enhance the reliability of auditory encoding in NCM.

GABAergic synapses: their plasticity and role in sensory cortex - See more at: http://journal.frontiersin.org/Journal/10.3389/fncel.2014.00091/abstract#sthash.l5jGe6MC.dpuf

“…The varied response properties of GABAergic neurons make them ideal candidates to modulate the activity of excitatory neurons during sensory processing. In vivo pharmacological manipulation of GABAergic transmission alters receptive fields properties in a number of different species and cortical regions, suggesting a role for cortical inhibition in controlling the stimulus preference and receptive field structure of excitatory neurons (Sillito, 1975 , 1979 ; Sillito et al, 1980 ; Kyriazi et al, 1996 ; Tremere et al, 2001 ; Li et al, 2002 ; Foeller et al, 2005 ; Jeong et al, 2009 ; Razak and Fuzessery, 2009 ; Isaacson and Scanziani, 2011 ; Katzner et al, 2011 ). However, the results of grossly disrupting or augmenting inhibition in cortex do not provide evidence that GABAergic neurons dynamically shape receptive fields, and their contribution to shaping the receptive fields of glutamatergic neurons is hotly debated (Isaacson and Scanziani, 2011 ; Liu et al, 2011 ; Wu et al, 2011 ; Priebe and Ferster, 2012 ).…”