Download When Does `Personhood` Begin? - School of Medicine, Queen`s

When Does `Personhood` Begin?
Teaching how neural development
might inform the abortion issue.
R. David Andrew
Professor, Centre for Neuroscience Studies,
Queen`s University,
Kingston, ON, Canada K7L 3N6
[email protected]
If the human brain was simple to understand, we’d be too simple to understand it.
- Anonymous medical student
If the human brain was simple to understand, we’d be
too simple to understand it.
- Anonymous medical student
[email protected]
RATIONALE
The public and our lawmakers can use input from
neuroscientists to make better informed decisions on
abortion policy. An important question needs to be
addressed:
When does
complexity?
the
developing
brain
take
on
human
This presentation was created to provide information to
students and the lay public about fetal brain formation and
when `human` characteristics come on-line during fetal
development.
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The neocortex is comprised of several layers of
nerve cells that cover the cerebral hemispheres.
It is a vast interconnected network of several billion
neurons.
neocortex
While the neocortex is only a few
millimetres thick, flattened out it covers 3
square metres of brain surface.
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Neocortex under the microscope
Most of our cortex (the covering of the brain) has formed recently in
evolution…hence the term ‘new’ or `neo`cortex
Characteristics:
• Pyramid- shaped (red) and star-shaped nerve cells arranged in 6
layers
• Many nerve processes course vertically through neocortex
• Appearance and function of neocortex varies depending on the
region
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Neocortical
Histology
Different staining
techniques reveal
different neuronal
components of the
6 layers.
-from Nolte, The Human Brain, Mosby
Elsevier
The neocortex and information flow…
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First,
`Primary` neocortical
regions (in color)
receive sensory
information (seeing,
hearing, touch, pain)
about our
surroundings.
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- Netter`s Concise Neuroanatomy, Saunders
Then…
`Primary` sensory
areas relay
information to their
own `association`
areas about sight
(blue), hearing
(purple) and
touch/pain (green).
- from Nolte, Neuroscience, Elsevier
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Then…
the association
areas relay their
information (black
and blue arrows)
to higher
association areas.
These areas then send
their highly integrated
sensory and emotional
information to the
motor regions (red
arrows) that control
our muscles.
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In this way, we respond to complex sensory
information with the proper motor actions.
-from Nolte, Neuroscience, Elsevier
To summarize…
Receives sensory
information
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Integrates that
information
Controls appropriate
motor responses
-from Nolte, The Human Brain, Mosby Elsevier
The computations of the vast cellular network that
comprises the neocortex are responsible for our distinctly
human traits:
• complex language
• precision movements of the hands and eyes
• incredible memory storage
• the power of forethought
How do we know this?
1) Certain neocortical regions have clear relationships
with these human traits…
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For example, certain neocortical regions are indispensible
for language…
Broca‘s area contains
motor programs with
instructions for speaking
Wernicke‘s area
contains neurons for the
formulation of language
Destruction of Wernicke's area leaves Broca's area unchecked, so
that words can be produced without regard for their meaning.
-from Nolte, The Human Brain, Mosby Elsevier
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Frontal neocortex is associated with mood,
planning, social skills
In the patient above, the frontal cortex was damaged by an explosion that blew an
iron bar into his head. The subject lived, but with severe disturbances to his mood as
well as his abilities to make plans and to properly socialize.
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-from Nolte, The Human Brain, Mosby Elsevier
Frontal neocortex is also associated with…
(judging emotional states)
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-from Nolte, The Human Brain, Mosby Elsevier
2) We lose our intelligence and memory when large
areas of neocortex are damaged.
For example, the victim of Alzheimer’s disease suffers a
progressive degeneration of the neocortex. So many
nerve cells eventually wither away, that the brain’s surface
literally shrivels up. The result is a slow but steady fading
of memories that once spanned an entire lifetime.
neocortex
While no one would argue that a patient with
advanced dementia is no longer a human
being, their four distinctly human traits noted
earlier are severely compromised.
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3) Human traits cannot arise unless the neocortex develops.
Some babies are actually born without a neocortex. By a cruel developmental
accident, the cells destined to become neocortical neurons fail to flourish.
The result is a newborn brain as smooth as a rabbit’s or rat’s. These
Lissencephalic (smooth-brained) infants remain profoundly mentally retarded.
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4) Really smart animals have lots of neocortex
Consider why your dog does not watch World
Federation Wrestling or access the Home Shopping
Network. It’s because only the most highly evolved
animals possess the extensive neocortex required for
such complex tasks.
The proliferation is most
obvious in the primates
(monkeys, humans) and
cetaceans (whales, dolphins),
the mammals known for their
impressive social interactions
and communicative skills
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5) Ontogeny (fetal development) repeats phylogeny
(evolutionary development). That is, the embryonic development of an
individual organism (its ontogeny) follows a similar path as the evolutionary
history of its species (its phylogeny).
Our arms have similar (homologous) components that have evolved
different functions in different mammals...
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-from Nolte, The Human Brain, Mosby Elsevier
5) Ontogeny repeats phylogeny…con`d
human
In particular, the
cerebral
hemispheres
(gray) have
expanded greatly
in humans…
Likewise, most
parts of the brain
have homologues
that have evolved
differently in each
mammal...
rat
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-from Nolte, The Human Brain, Mosby Elsevier
5) Ontogeny repeats phylogeny…con`d
It turns out that the
development of the
neocortex in the
human fetus
wonderfully reflects …
…our evolutionary
development, a concept
that biologists term
“ontogeny repeating
phylogeny”
The more advanced the
neocortical development,
the more advanced the
animal.
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Increasing
intelligence
Ontogeny repeats phylogeny…con`d
There is some scientific controversy here. The German zoologist
Ernst Haeckel oversimplified the concept…and presented some
bogus fetal drawings to support it. Nevertheless, any biology
student taking undergrad Embryology can site examples (fetal
development of the heart, of the major blood vessels, of the
kidneys) where the system`s evolutionary history is apparent.
See http://en.wikipedia.org/wiki/Recapitulation_theory
6) A 3-month human fetus is not very smart.
Why is that?
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9 months
First, the fetal brain grows roughly
in proportion to the body...
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4.5 months gestation
7 months gestation
6 month old infant
III
V
III
V
200 μm
Second, the neocortical connections
among neurons only start forming at
~4 months gestation…
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III
V
Third, dendritic spines, which receive input from other
neurons, only become apparent at ~5 months gestation.
Branching patterns of hippocampal neurons of
human fetus during dendritic differentiation.
Paldino AM, Purpura DP.
Exp Neurol. 64:620-31 (1979)
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Note that nerve cell development in neocortex starts in
the mid-gestational months, but continues at a
phenomenal rate, even following birth…
[email protected]
-from Nolte, The Human Brain, Mosby Elsevier
The cerebellum helps
provide smooth,
coordinated body
movement
The cerebellar cortex
also starts forming
late…at about 12 weeks
(~3 months) gestation.
Again, it takes many
months for the neurons
to make their proper
connections.
-from Nolte, The Human Brain
So for the preceding six reasons, the neocortex is considered to
be responsible our distinctly human traits of:
9 complex language
9 precision movements of the hands and eyes
9 incredible memory storage
9 and the power of forethought.
It is commonly (and mistakenly) believed that the brain is
well established early in human fetal development…
…actually at 7 weeks
gestation, it`s only the size
of a pin-head.
So where does this idea come from ?
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First, textbooks and websites usually do not accurately
portray how small the first trimester brain actually is…the
figures are usually illustrated to show detail rather than
proportion.
Disproportionate
Proportionate
25 days
Nine months
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Nine months
Second, the Internet can spread mis-information…
From The Pregnancy Care Center
http://www.pcceureka.org/
Day 20 “Foundations” (my quotes) of the brain, spinal cord
vague
and nervous system are already established.
Day 21 The heart begins to beat.
Day 28 The backbone and muscles are forming.
Arms, legs, eyes and ears have begun to show.
Day 30 The heart is pumping increasing quantities
of blood through the circulatory system.
Day 35 Five fingers can be discerned in the hand.
Day 40 Brain waves can be detected and recorded.
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x
Brain waves are not detectable at 40 days gestation.
Remember, the brain is the size of a pin-head at that time point…
In fact...EEG recording in the premature infant indicates that the
neocortex is not actively involved in perceiving what we see until
gestational weeks 34-36.
Colonnese, M. et al. Developmental switch in sensory signal processing in
visual cortex prior to the onset of vision.
Society for Neuroscience Meetings 2008, abstract 724.8
Third, ultrasound images
graphically reveal the little
heart beating, fingers and
toes developing, and limbs
moving in space.
Yet these developmental
milestones do not require
higher brain function. The
heart pumps on its own and muscles
contract in response to commands
from the spinal cord.
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It is not until gestational months 5-6 that our
brain regions that drive awareness and the
conscious control of movements even begin
to hard-wire.
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Many lay people seem comfortable with the
notion of a human being instantly created at
conception.
However this presentation has discussed
evidence that our brain`s transition toward
`personhood` if you like, is gradual and
immensely intricate. In the first trimester there is
no neocortex. By the third trimester, the fetal
neocortex is accelerating toward the
unimaginable complexity seen in the full-term
infant.
It is the development of the neocortex in the last
half of gestation that is absolutely essential for
our human qualities to emerge.
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Clearly the period when we acquire our
`personhood` is not a discrete time point, but
spans many weeks during mid-gestation. It is not
a sudden event.
By using our understanding of brain
development, neuroscientists are well positioned
to inform lawmakers and the public on abortion
guidelines.
Why is no one asking?
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Neuroscientists speak
The anti-abortion movement's members would have us believe that their concern for fetal life is derived from a
broad base of respect for human life and a concern for human pain, suffering, and violence. The production of the
film The Silent Scream is an attempt to dramatize those concerns by illustrating alleged fetal pain and suffering
during an abortion procedure.
The perception of pain is a complex biological and psychological phenomenon that involves states of
"consciousness" which can probably never be fully understood or known for certain stages of fetal development.
Relevant to this inquiry are certain neurobiological and biobehavioral facts concerning states of "consciousness"
and "pain" perception during fetal development that should be known by all concerned citizens.
Patricia A. Jaworski has produced an audio tape, "Thinking About the Silent Scream," in which she interviews
several internationally renowned neuroscientists on fetal brain development, the alleged fetal perception of "pain,"
and alleged fetal "personhood." Some of the highlights of those interviews are summarized in the following
paragraphs.
Dr. Michael Bennett, chairman of the neuroscience department of Albert Einstein Medical School, when asked
whether a brain exists at conception and whether there can be a person without a brain, answered with an
unequivocal "no!" to both questions. It was pointed out that the human brain has approximately 100 billion brain
cells and that there are an estimated 100 trillion connections between neurons in the brain. This extraordinary
neuronal "interconnectivity" provides the neurostructural foundation for complex perceptions and "personhood"
and takes many months and often years to fully develop and function.
Dr. Patricia Goldman-Rakic, professor of neuroscience at Yale University Medical School (deceased), emphasizes
that brain neurons do not exist prior to four weeks in utero, that the peak period for brain neuron development is
from two to five months in utero, and that the existence of neurons, per se, does not indicate the existence of a
developed, functioning brain. Once the brain cell is born, there is a long process of migration of brain cells that
occurs mainly from two to six months in utero during which the brain cells move (migrate) to their final destination
in the brain. An even longer process of development makes possible the "interconnectivity" of brain cells which is
absolutely essential for sensation, perception, conscious experience, thought, and behavior. The formation of
brain synapses that make possible brain cell communication does not begin until about the third month in utero,
and most are formed after birth.
…CON`D
….CON`D
Dr. Clifford Grobstein, former chairman of the Department of Biology at Stanford University and now at the
University of California at San Diego, highlights the complexity of brain development by noting that the
brain does not develop uniformly. For example, certain parts of the brain develop earlier and some later.
The cerebral neocortex that is responsible for complex perceptions is one of the last to develop.
Dr. Dominick Purpura, dean of Albert Einstein Medical School, has been studying human brain
development since 1974 with his research on mental retardation. Dr. Purpura emphasizes that there are a
minimum number of neurons and synaptic connections that are necessary before the qualities of
"humanness" and "personhood" can be developed and that this capacity begins to occur in the middle of
the last trimester. Thus, about twenty-eight to thirty weeks in utero is the minimal time for the beginning of
this capacity—"It can't begin earlier," according to Dr. Purpura.
Dr. Purpura also emphasizes that critical changes are seen in the fetal brain wave pattern at thirty-one
weeks when the brain waves become more organized and, thus, meuninglul; the first signs of sleep and
wakefulness are not observed until a few weeks later. It is emphasized that all cells have electrical
potentials and that the mere presence of such signals, per se, does not mean that the capacity for
complex perceptions or "personhood" exists. How these neuronal signals become organized and reflect
underlying neuronal and structural organization is fundamental to understanding the basic neurobiological
pnnciple that structure precedes function.
Thus, it can be concluded that neither pain perception nor personhood exists at conception and that the
capacity for personhood may only begin at twenty-eight to thirty weeks in utero.
----------------------------------------------------------------------------------------------------------------------------------------Appendix C in Doerr, Edd and Prescott, James W. (Eds.): Abortion Rights and Fetal 'Personhood',
2nd Ed. Long Beach (1990); originally published in The Humanist, September/October l986.