1. Illing RB, Cao QL, Forster CR, Laszig R. Auditory brainstem: development and plasticity of GAP-
   43 mRNA expression in the rat. J Comp Neurol. 1999 Sep 20;412(2):353-72.
   
2. Roebuck TM, Mattson SN, Riley EP (1998) A review of the neuroanatomical findings in children
   with fetal alcohol syndrome or prenatal exposure to alcohol. Alcoholism, Clinical and
   Experimental Research 22:339-44
   
3. Illing RB. (2004) Maturation and plasticity of the central auditory system.  Acta
   Otolaryngol Suppl. 2004 May;(552):6-10.
   

5 -  Neural plasticity
Illing et al (1999) studied production of a growth- and
plasticity-associated protein (GAP-43) in the auditory
system of laboratory rats [1].  This protein is
produced at high levels in every nerve cell during
early stages of synapto-genesis, and then its
expression is down regulated in most neurons.  
Persistence of GAP-43 in brainstem auditory nuclei
suggests the potential for plastic remodeling,
dependent upon sensory experience and learning.  
Illing et al. inferred that a significant amount of
ongoing synaptic tuning continues within auditory
nuclei such as the superior olivary complex and
inferior colliculi.  Assuming the same tuning potential
remains active in primates and humans, what is the
result of perinatal damage to these highly active
auditory centers?

Illing et al. also discussed the effects of
over-expression of GAP-43 in one strain of
genetically defective mice, which leads to
spontaneous formation of aberrant neuronal
connections with disturbances of axonal path finding.  
Prenatal exposure to alcohol and other toxic
substances can lead to heterotopias or ectopic
overgrowth of neural tissues in the brain, and this
may be due to interference of these substances with
the normal process of down regulation with
maturation [2].

What has been learned about the biochemistry of
development and neurotransmission is clearly just a
small fraction of all there is to know.  How do
excitatory and inhibitory neurons in the brainstem
pathways interact to provide multiplexing of auditory
signals?  At what level are multiple frequencies and
other time and intensity varying components
attributed to a particular sound source, and how are
sounds from moving objects tracked?  How is
selective focus on a specific sound source
maintained?  Answers to these questions and more
are needed for full understanding of the mechanisms
of auditory attention, joint attention, social awareness,
and language development.  A great deal more
research is needed before pharmacological
treatments based on more than trial and error can be
developed for attention deficits that underly problems
like auditory agnosia.

Full References

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References

1. Illing RB et al. (1999)  Auditory
   brainstem: development and
   plasticity of GAP-43 mRNA
   expression in the rat
   
2. Roebuck TM et al. (1998) A
   review of the neuroanatomical
   findings in children with fetal
   alcohol syndrome or prenatal
   exposure to alcohol.
   
3. Illing RB. (2004) Maturation and
   plasticity of the central auditory
   system.