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Bioacoustic papers in Natureâââââ

Subject: Bioacoustic papers in Natureâââââ
From: "XIAO, Jianqiang" <>
Date: Thu, 17 Jun 2010 13:52:25 -0400
Nature  465
Editor's Summary
17 June 2010
Fine-tuning receptive fields
In order to build a proper and stable representation of the auditory
world, neonatal rodents exhibit a significant degree of circuit
plasticity, allowing for sensitivity to the pattern of sensory inputs.
During this time, neurons construct a receptive field, one that relies
upon a particular balance of excitatory and inhibitory inputs, yet it
is unknown as to how this balance is formed. Two studies published in
this issue of Nature reveal contrasting views as to how the mature
system develops. Excitation and inhibition were found to be equally
strong upon hearing onset in each study. But whereas Dorrn et al. find
evidence for an experience-dependent refinement of inhibition as the
receptive fields develop, Sun et al. observed a fine adjustment in the
excitatory input strength to produce a shifted balance. Nevertheless,
taken together, both studies point towards a fine adjustment of
synaptic inputs as the force behind the production of mature receptive
fields, as opposed to more radical changes such as input pruning.
Letter: Fine-tuning of pre-balanced excitation and inhibition during
auditory cortical development

Nature  Volume: 465, Pages: 927–931, Date published: 17 June 2010,
DOI: 10.1038/nature09079
Yujiao J. Sun, Guangying K. Wu, Bao-hua Liu, Pingyang Li, Mu Zhou,
Zhongju Xiao, Huizhong W. Tao & Li I. Zhang
Letter: Developmental sensory experience balances cortical excitation
and inhibition
Functional receptive fields of neurons in sensory cortices undergo
progressive refinement during development. Such refinement may be
attributed to the pruning of non-optimal excitatory inputs, reshaping
of the excitatory tuning profile through modifying the strengths of
individual inputs, or strengthening of cortical inhibition. These
models have not been directly tested because of the technical
difficulties in assaying the spatiotemporal patterns of functional
synaptic inputs during development. Here we apply in vivo whole-cell
voltage-clamp recordings to the recipient layer 4 neurons in the rat
primary auditory cortex (A1) to determine the developmental changes in
the frequency–intensity tonal receptive fields (TRFs) of their
excitatory and inhibitory inputs. Surprisingly, we observe co-tuned
excitation and inhibition immediately after the onset of hearing,
suggesting that a tripartite thalamocortical circuit with relatively
strong feedforward inhibition is formed independently of auditory
experience. The frequency ranges of tone-driven excitatory and
inhibitory inputs first expand within a few days of the onset of
hearing and then persist into adulthood. The latter phase is
accompanied by a sharpening of the excitatory but not inhibitory
frequency tuning profile, which results in relatively broader
inhibitory tuning in adult A1 neurons. Thus the development of
cortical synaptic TRFs after the onset of hearing is marked by a
slight breakdown of previously formed excitation–inhibition balance.
Our results suggest that functional refinement of cortical TRFs does
not require a selective pruning of inputs, but may depend more on a
fine adjustment of excitatory input strengths.

Anja L. Dorrn, Kexin Yuan, Alison J. Barker, Christoph E. Schreiner &
Robert C. Froemke
Letter: Developmental sensory experience balances cortical excitation
and inhibition
Nature  Volume: 465, Pages: 932–936, Date published: 17 June 2010,
DOI: 10.1038/nature09119
Early in life, neural circuits are highly susceptible to outside
influences. The organization of the primary auditory cortex (A1) in
particular is governed by acoustic experience during the critical
period, an epoch near the beginning of postnatal development
throughout which cortical synapses and networks are especially
plastic. This neonatal sensitivity to the pattern of sensory inputs is
believed to be essential for constructing stable and adequately
adapted representations of the auditory world and for the acquisition
of language skills by children. One important principle of synaptic
organization in mature brains is the balance between excitation and
inhibition, which controls receptive field structure and
spatiotemporal flow of neural activity, but it is unknown how and when
this excitatory–inhibitory balance is initially established and
calibrated. Here we use whole-cell recording to determine the
processes underlying the development of synaptic receptive fields in
rat A1. We find that, immediately after the onset of hearing,
sensory-evoked excitatory and inhibitory responses are equally strong,
although inhibition is less stimulus-selective and mismatched with
excitation. However, during the third week of postnatal development,
excitation and inhibition become highly correlated. Patterned sensory
stimulation drives coordinated synaptic changes across receptive
fields, rapidly improves excitatory–inhibitory coupling and prevents
further exposure-induced modifications. Thus, the pace of cortical
synaptic receptive field development is set by progressive,
experience-dependent refinement of intracortical inhibition.



XIAO, Jianqiang, Ph.D.
Research Associate
Psychology Department
Rutgers University
152 Frelinghuysen Road
Piscataway, NJ 08854

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