psychology professor at the University of Maryland, Robert Provine, is one of the few other
researchers into yawning. He found the basic yawn lasts about six seconds and they come in
bouts with an interval of about 68 seconds. Men and women yawn or half-yawn equally often,
but men are significantly less likely to cover their mouths which may indicate complex
distinction in genders.” A watched yawner never yawns,” Professor Provine said. However, the
physical root of yawning remains a mystery. Some researchers say it’s coordinated within the
hypothalamus of the brain, the area that also controls breathing.
F
Yawning and stretching also share properties and may be performed together as parts of a
global motor complex. But they do not always co-occur – people usually yawn when we
stretch, but we don’t always stretch when we yawn, especially before bedtime. Studies by J.I.P,
G.H.A. Visser and H.F. Prechtl in the early 1980s, charting movement in the developing fetus
using ultrasound, observed not just yawning but a link between yawning and stretching as
early as the end of the first prenatal trimester.
G
The most extraordinary demonstration of the yawn-stretch linkage occurs in many people
paralyzed on one side of their body because of brain damage caused by a stroke. The
prominent British neurologist Sir Francis Walshe noted in 1923 what when these hemiplegics
yawn, they are startled and mystified to observe that their otherwise paralyzed arm rises and
flexes automatically in what neurologists term an “associated response.” Yawning apparently
activates undamaged, unconsciously controlled connections between the brain and the cord
motor system innervating the paralyzed limb. It is not known whether the associated response
is a positive prognosis for recovery, nor whether yawning is therapeutic for reinnervation or
prevention of muscular atrophy.
H
Clinical neurology offers other surprises. Some patients with “locked-in” syndrome, who are
almost totally deprived of the ability to move voluntarily, can yawn normally. The neural circuits
for spontaneous yawning must exist in the brain stem near other respiratory and vasomotor
centers, because yawning is performed by anencephalic who possess only the medulla
oblongata. The multiplicity of stimuli of contagious yawning, by contrast, implicates many
higher brain regions.
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