A prominent feature of fetal behavioral state is the predominance of long
and frequent periods of REM sleep. In sheep REM sleep episodes average about 10 minutes in
length, and they account for roughly 45% of the total time.
REM sleep is characterized by low voltage, high frequency electrocortical
activity and considerable electrooculogram activity indicating rapid movement of the fetal
eyes.
REM sleep is characterized by high levels of fetal brain metabolic activity as
well as cerebral blood flow as indicated in this study. It is believed that significant
amounts of functional excitation of the brain occuring during REM sleep may enhance the
structural maturation within the central nervous system. This brain
"autostimulation" may be especially important during fetal life when
non-auditory sensory inputs are minimal or absent.
Click here to listen to a clip of
"We Are the Boys From Old Florida" as recorded in air, inside the uterus of a
sheep, and from the fetal inner ear (cochlear microphonic).
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