8 -  Importance of auditory nuclei
Because of their need for sustained energy
production, the brainstem nuclei of high metabolic rate
can be expected to be vulnerable, from prenatal life
into old age, to oxygen deficiency, toxic substances,
or excess metabolic end products such as bilirubin.  
The auditory system appears to be especially
sensitive to the cumulative effects of exogenous and
endogenous insults that are part of the process of
aging [1-3].  Decline in hearing is common with
advancing age, but even by the time of adolescence
learning a new language simply by hearing it becomes
increasingly difficult.  This indicates progressive loss
of auditory acuity beginning in the first decade of life.

As noted in chapter xx, Rapin (1997) suggested that
the disorder of language development in some
children with autism may be due to “verbal auditory
agnosia,” an inability to extract syllables and words
from rapid streams of speech [4].  We may all begin to
experience some degree of verbal auditory agnosia
by the time of adolescence.  A new language learned
after adolescence is rarely mastered without a foreign
accent.  With maturation, we seem to lose awareness
of acoustic features essential for learning a language
through hearing.

What is especially difficult is trying to follow streams of
speech in a foreign language.  New sounds are not
easily recognized and usually simulated by those of
the mother tongue.  Sound substitutions made by
foreigners are often hilarious to native speakers of a
language, and often identify the nationality of the
speaker.  This is a common experience for adult
learners of a new language and in no way viewed as
an impairment of auditory function.  That we do not
recognize this loss of acuity as we mature may partly
explain why we fail to see it as disabling when it occurs
in a young child.

Based on its high metabolic activity the auditory
system appears to have important functions in many
mammalian species.  The auditory system clearly has
special importance for communication and
socialization in humans.  It might seem less of a
handicap to be deaf than blind.  But parents of a child
born deaf soon learn how essential hearing is for
learning language without special instruction.

Full References

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References

1. Sinha UK et al. (1993)
   Auditory system
   degeneration in Alzheimer's
   disease.
   
2. Caspary DM et al. (1995)
   Central auditory aging:
   GABA changes in the
   inferior colliculus.  
   
3. O'Mahony D et al. (1994)
   Primary auditory pathway
   and reticular activating
   system dysfunction in
   Alzheimer's disease.  
   
4. Rapin I (1997)  Autism.
   

1. Sinha UK, Hollen KM, Rodriguez R, Miller CA (1993) Auditory system degeneration in
   Alzheimer's disease.  Neurology 43:779-85.
   
2. Caspary DM, Milbrandt JC, Helfert RH (1995) Central auditory aging: GABA changes in
   the inferior colliculus.  Experimental Gerontology 30:349-360.
   
3. O'Mahony D, Rowan M, Feely J, Walsh JB, Coakley D (1994) Primary auditory pathway
   and reticular activating system dysfunction in Alzheimer's disease.  Neurology 44:2089-
   94.
   
4. Rapin I (1997)  Autism.  New England Journal of Medicine 337:97-104.