Monday, 12 August 2013

Electrical Signatures of Consciousness in the Dying Brain

Electrical Signatures of
Consciousness in the Dying Brain
Aug. 12, 2013 — The "near-death
experience" reported by cardiac
arrest survivors worldwide may be
grounded in science, according to
research at the University of Michigan
Health System.
Whether and how the dying brain is
capable of generating conscious
activity has been vigorously debated.
But in this week's PNAS Early Edition ,
a U-M study shows shortly after
clinical death, in which the heart
stops beating and blood stops flowing
to the brain, rats display brain
activity patterns characteristic of
conscious perception.
"This study, performed in animals, is
the first dealing with what happens
to the neurophysiological state of the
dying brain," says lead study author
Jimo Borjigin, Ph.D., associate
professor of molecular and
integrative physiology and associate
professor of neurology at the
University of Michigan Medical
School.
"It will form the foundation for
future human studies investigating
mental experiences occurring in the
dying brain, including seeing light
during cardiac arrest," she says.
Approximately 20 percent of cardiac
arrest survivors report having had a
near-death experience during clinical
death. These visions and perceptions
have been called "realer than real,"
according to previous research, but it
remains unclear whether the brain is
capable of such activity after cardiac
arrest.
"We reasoned that if near-death
experience stems from brain activity,
neural correlates of consciousness
should be identifiable in humans or
animals even after the cessation of
cerebral blood flow," she says.
Researchers analyzed the recordings
of brain activity called
electroencephalograms (EEGs) from
nine anesthetized rats undergoing
experimentally induced cardiac
arrest.
Within the first 30 seconds after
cardiac arrest, all of the rats
displayed a widespread, transient
surge of highly synchronized brain
activity that had features associated
with a highly aroused brain.
Furthermore, the authors observed
nearly identical patterns in the dying
brains of rats undergoing
asphyxiation.
"The prediction that we would find
some signs of conscious activity in
the brain during cardiac arrest was
confirmed with the data," says
Borjigin, who conceived the idea for
the project in 2007 with study co-
author neurologist Michael M. Wang,
M.D., Ph.D., associate professor of
neurology and associate professor of
molecular and integrative physiology
at the U-M.
"But, we were surprised by the high
levels of activity," adds study senior
author anesthesiologist George
Mashour, M.D., Ph.D., assistant
professor of anesthesiology and
neurosurgery at the U-M. " In fact, at
near-death, many known electrical
signatures of consciousness exceeded
levels found in the waking state,
suggesting that the brain is capable
of well-organized electrical activity
during the early stage of clinical
death."
The brain is assumed to be inactive
during cardiac arrest. However the
neurophysiological state of the brain
immediately following cardiac arrest
had not been systemically
investigated until now.
The current study resulted from
collaboration between the labs of
Borjigin and Mashour, with U-M
physicist UnCheol Lee, Ph.D., playing
a critical role in analysis.
"This study tells us that reduction of
oxygen or both oxygen and glucose
during cardiac arrest can stimulate
brain activity that is characteristic of
conscious processing," says Borjigin.
"It also provides the first scientific
framework for the near-death
experiences reported by many cardiac
arrest survivors."

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