Vulnerability and protective mechanisms
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Blood flow and aerobic metabolism
have been found many times over to
be highest in the auditory system, and
especially in the inferior colliculus
[1-4, 6-7, 8-12, 13-22].
Except under catastrophic situations like
those listed to the left, protective
mechanisms come into play that maintain
activity in the inferior colliculi and other
brainstem nuclei of high metabolic rate.
A bilaterally symmetric pattern of
brainstem damage is found after
catastrophic disruption of metabolic
processes, and the inferior colliculi
are prominently affected:
In victims resuscitated after
cardiac arrest [23-31], or
During an episode of hypoxia or partial
circulatory insufficiency, the inferior
colliculi will be preserved at the expense
of the cerebral cortex and brainstem
nuclei of lesser metabolic rate.
For example, hemoglobin releases oxygen
in exchange for the metabolic end product
carbon dioxide (the Bohr effect). High
amounts of carbon dioxide produced in
the metabolically most active nuclei, like
the inferior collciculus, will ensure oxygen
delivery during hypoxia, but then
hemoglobin may have no oxygen to
deliver to areas of lesser metabolic activity
like the cerebral cortex.
In chronic alcohol abuse [43-47],
and
By other toxic substances that
disrupt aerobic metabolism [48-49,
50-54, 56-61]
