Speech understanding
Subjects & tests
Predicted results
Hypotheses & rationale

References
Auditory agnosia
Asphyxia at birth
Human infants
Functional MRI
Presbyacusis
Fetal alcohol syndrome
fMRI of language processing
Trophic transmitters
Longterm outcome
Myelin maturation
Learning to speak
Kanner autism
Metabolism in the brain
Vasodilation response
The Bohr effect
Circulatory arrest
Brainstem damage
Thiamine deficiency
Autism & prenatal alcohol
Autism & valproic acid
Autism & infections
Autism & PKU
Autism & genetic disorders
Autism & medical disorders
Autism & perinatal problems
(4) Why the brainstem is usually less susceptible to damage than
the cerebral cortex
Blood flow and metabolism are higher in the inferior colliculi than anywhere else in the
brain [
48-52].  Figure 13 shows the high level of blood flow in nuclei of the brainstem
auditory pathway, demonstrated by rapid distribution of a radioactive tracer.  Sokoloff
(1981) commented, "The inferior colliculus is clearly the most metabolically active
structure in the brain" [50].
 Despite its high metabolic activity, the inferior colliculi are not predictably affected by
oxygen insufficiency.  Under hypoxic conditions, protective mechanisms like (a)
vasodilation go into action as a means of sparing this metabolically important nucleus
[
53, 54].  Also,
(b) hemoglobin delivers oxygen more readily to the most metabolically active tissues,
those producing the highest levels of carbon dioxide (the Bohr Effect) [
55].  
Damage restricted to the brainstem only occurs when total interference with aerobic
metabolism occurs; Janzer and Friede (1980) referred to brainstem pathology as
"cardiac arrest encephalopathy" [
56]; this was the case in monkeys subjected to
several minutes of total asphyxia at birth [
11, 12].
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