Humanity? Maybe It's in the Wiring
New York Times
By SANDRA BLAKESLEE
Published: December 9, 2003
Neuroscientists have given up looking for the seat of the soul, but
they are still seeking what may be special about human brains, what
it is that provides the basis for a level of self-awareness and complex emotions unlike those of other animals.
Most recently they have been investigating circuitry rather than
specific locations, looking at pathways and connections that are
central in creating social emotions, a moral sense, even the feeling
of free will.
There are specialized neurons at work, as well large, cigar-shaped
cells called spindle cells. The only other animals known to have such cells are the great apes. These neurons are exceptionally rich in filaments. And they appear to broadcast socially relevant signals all over the brain.
The body, it turns out, is as important as the brain. Dr. Antonio
Damasio, a neurologist at the University of Iowa Medical Center and
the author of the book "Looking for Spinoza: Joy, Sorrow and the
Feeling Brain," has pioneered the argument that emotions and feelings
are linked to brain structures that map the body. From human social
emotions, he said, both morality and reason have grown.
Similar ideas were advanced in simpler form more than a century ago.
Now, researchers can point to specific aspects of brain structure
that suggest how our forebears came to develop complex social
emotions, culture and other quintessential human behaviors.
The search for brain differences has not been easy. Mammalian brains
are extraordinarily similar. All contain an outer rind, or cortex.
The human cortex, where intelligence lies, is simply a lot bigger
than that of other creatures given the human body's size.
But the size of the brain is not everything. One important feature of
more complex brains is that they are rich in circuits linked cells
from various parts of the brain that become active at the same time.
Imagine a Christmas tree with millions of lights, each representing a
cell group. The thought of dogs would activate a small set of lights.
The thought of a beloved dog that died last year would activate some
of the same lights plus others.
The thought of a cat would activate yet another set with some overlap
because animals are involved. Thinking about a sunset would activate
whole new sets of lights with no overlap. Once a thought is complete,
all the lights or neurons fall silent, waiting to be called into play
in different combinations when new thoughts arise.
Some sets of lights are found in structures that serve as major hubs
for thinking and feeling. For example, a brain region called the
anterior cingulate a hub from which many circuits branch out is
almost always active when human subjects are experiencing emotions or
need to think about things that are difficult. Any conflict of any
sort, any reward, and the anterior cingulate starts buzzing.
At least that is the judgment of the researchers who track increased
blood flow with brain scans called functional magnetic resonance
imaging.
One of the first circuits studied in the 1940's involved the sense of
touch. Sensations from the skin, including pain and temperature, were
found to be carried by nerve fibers to a part of the brain devoted to
bodily sensation. Less distinct sensations from viscera and internal
organs went to a small region called the insula.
Or so the thinking of the time went. But Dr. Arthur Craig, a
functional neuroanatomist at the Barrow Neurological Institute in
Phoenix, says this classic view is incorrect for most sensations.
In a series of recent articles published in leading neuroscience
journals, Dr. Craig has laid out a new wiring diagram for how the
body talks to the brain. Tissues from all over the body, from skin
surface to muscles, contain nerve endings or sensors that relay
information, via long nerves, to the upper spinal cord. From this
information come sensations including sharp pain, burning pain, cool
or warm temperature, itching, muscle contraction, muscle burn because
of lactic acid, joint movements, soft touch, mechanical stress,
tickling, flushing, hunger and thirst.
The target cells, called Lamina 1 neurons, together make up a map of
the state of the body. They are the first of several steps in the
sorting and transmitting of sensory information, through structures
in the brain stem and midbrain to the cortex.
The line ends at two thumb-size parts of the cortex called the
insula, one on the left and one on the right side of the brain. But
the crucial stop along the way may be a nucleus of cells in the back
of the thalamus with the intimidating name of the posterior
ventromedial nucleus, VMpo for short.
This structure hardly exists in most mammals. It is the size of a
grain of sand in the macaque monkey, but relatively enormous in
humans the size of a pistachio nut. It collects information on
bodily states like temperature or the need for water, that need to be
monitored to keep the body stable, in equilibrium. A nearby
structure, another similar nucleus, also collects sensory news from
internal organs. Each sends the information on to the pair of
insulae.
In brain imaging studies the insulae show increased blood flow when
people are exposed to disgusting odors, bad tastes, light touch or
feel itching, muscle fatigue, stomach pain, thirst and most other
body sensations. Because of this, scientists think that this
collection of neurons contains a richer and more detailed map of the
state of the body. Just as a map on the computer screen can grow more complex as cities, roads, even buildings are added, the brain seems
to be making ever more complex constructions of feelings to represent
what is going on in the body. How this happens is still a mystery.
But the insula, Dr. Craig said, is "a system that represents the
material me."
In each insula information becomes feelings. Self-awareness emerges,
Dr. Craig said. Other animals have basic emotions, but the consensus
is that most lack self-awareness and complex emotions because they
lack brain structures like the VMpo and have insulae that are much
less complex.
T
here is a final step. Information from the left and right insula is
rerouted to the front part of the right insula where a new map is
created, with yet another level of feeling, yet another sense of what
is going on internally and in the world. This, say some neuroscientists, is where body states are translated into social emotions, which are the sorts of feelings that poets and novelists concentrate on &Mac247; love and hate, lust and disgust, cold calculation, hot tempers, sadness and happiness. If one feels heavy, or light, in the metaphorical sense, one is feeling it in the right anterior insula.
In scores of brain studies, this part of the insula is activated when
we recall sadness or anger, anticipate pain, feel panic or become
sexually aroused or have an emotional response to music. It lights up
when people view or imitate emotional expressions in others. And in
one study it showed activity when people experienced the pain of
being socially excluded.
A number of experiments show that the anterior insula is the main
area that is active when people experience self-awareness, the
realization that "it is my body that is moving," my physical self
moving through time.
In a separate line of research, Dr. John M. Allman, a neuroscientist
at the California Institute of Technology, and his colleagues have
delved below the level of brain structure to identify a special class
of neuron spindle cells that are relatively enormous cells that
collect information from one region of the brain and send it on to
other regions. They function like air traffic controllers for emotions. They seem to lie at the heart of the human social emotion circuitry, including a moral sense.
At a Society for Neuroscience meeting in New Orleans last month, Dr.
Allman reported finding spindle cells in an area called the frontoinsular cortex in only two species humans and African apes.
This is a region closely connected to the insula and part of the same
elaborate circuitry in which emotions are generated and experienced.
An adult human had 82,855 such cells, a gorilla had 16,710, a bonobo
had 2,159 and a chimp had 1,853. All had more spindle cells in the
right hemisphere than in the left.
This particular part of the cortex is a somewhat mysterious
region, Dr. Allman said. In brain imaging studies, it lights up when
people look at romantic partners; perceive unfairness, deception or
uncertainty about rewards; experience embarrassment; or, if they are
mothers, hear infants cry.
The area is part of the orbitofrontal cortex, a part of the brain that seems to have undergone an evolutionary leap forward as recently as 100,000 years ago. It is where autobiographical memories are retrieved and choices are made for governing future behavior. It is activated with moral quandaries and economic decision making.
Four years ago, Dr. Allman and his colleagues identified spindle cells in the anterior cingulate of humans, African apes and orangutans but not in any other species.
The anterior cingulate is an older part of the brain that participates in
autonomic functions like heart rate and blood pressure, generation of
vocalizations and the production and recognition of facial
expressions.
In humans, the experience of any intense emotion love,
anger, lust activates the anterior cingulate. It is active during
demanding tasks and when people make errors. The harder the task, the
more activation.Spindle cells probably first appeared 10 million to
15 million years ago in a common ancestor of apes, hominids and
humans, Dr. Allman said.
Today these rare neurons are 5 to 40 times as abundant in humans as in apes. Spindle cells may help people register the general appropriateness of transactions or events, he said. They are a teaching system that takes output from social emotion circuits I feel good about this, I don't feel good about that and sends it all over the cortex for further action to occur.
Spindle cells are not present at birth. They appear around age
4 months and gradually increase during the second and third year of
life, the same time that guilt and embarrassment appear. As children
develop a sense of moral judgment, the frontal lobes and spindle cell
system continue to expand.No neuroscientist would make a leap to say
that this is where the conscience or sense of free will is lodged.
But if one imagined a single location for these fundamental aspects
of human nature, this would be the place.
Schizophrenic symptoms and SPECT abnormalities in a coeliac patient: regression after a gluten-free diet.
De Santis A, Addolorato G, Romito A, Caputo S, Giordano A, Gambassi G, Taranto C, Manna R, Gasbarrini G.
Department of Internal Medicine, Catholic University, Rome, Italy.
A 33-year-old patient, with pre-existing diagnosis of 'schizophrenic' disorder, came to our observation for severe diarrhoea and weight loss.
Use of single photon emission computed tomography, (99mTc)HMPAO SPECT, demonstrated hypoperfusion of the left frontal brain area, without evidence of structural cerebral abnormalities. Jejunal biopsy showed villous atrophy. Antiendomysial antibodies were present.
A gluten-free diet was started, resulting in a disappearence of psychiatric symptoms, and normalization of histological duodenal findings and of (99mTc)HMPAO SPECT pattern.
This is the first case in which, in an undiagnosed and untreated coeliac patient with psychiatric manifestations, the (99mTc)HMPAO SPECT demonstrated a dysfunction of frontal cortex disappearing after a gluten-free diet.
Scans 'may damage infant brains'
British Medical Journal
2 January, 2004
Young toddlers may be most at risk
Doctors have been urged not to use powerful CT scans to assess possible brain injuries in young infants.
Researchers in Sweden say they have uncovered evidence that the scans may damage toddlers' brains.
Their study of more than 3,000 men who had scans before they were 18 months old found many went on to develop learning problems.
Writing in the British Medical Journal, the researchers called for new guidelines to warn doctors of the risk.
CT or computed tomography scans use ionising radiation to take pictures of the inside of the body. They are more detailed than conventional X-rays.
The risk and benefits of computed tomography scans in minor head trauma need re-evaluating
Dr Per Hall
They are used on patients with a wide range of suspected problems, from cancer to suspected brain injuries.
In recent years, doctors have started to use CT scans on young infants.
Previous studies have suggested that high doses of ionising radiation can damage the developing human brain.
Radiation therapy
Dr Per Hall and colleagues at the Karolinska Institute in Stockholm decided to carry out research to see if low doses of ionising radiation have a similar effect.
The researchers identified 3,094 men who had received radiation therapy as toddlers between 1930 and 1959.
They also obtained information on the intellectual capacity and school record of each of these men.
They found that the higher the dose of radiation the more likely these men were to suffer learning problems later in life.
They were also more likely to have dropped out of school.
The researchers suggested new guidelines are needed to ensure doctors do not use CT scans on young infants.
"The risk and benefits of computed tomography scans in minor head trauma need re-evaluating," they wrote.
"Computed tomography, which delivers high doses of ionising radiation, is increasingly being used in even young children after minor head trauma."
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