Emotion Affects Ability To Recall Events
Scientists Study How Better Memories Are Made
When
you remember an emotional event, your memory of it may be very accurate,
but you are likely to forget the events that preceded it, researchers
report.
"If an emotional event happens,
you remember it better," says lead researcher Dr. Ray Dolan, a professor
of neurology at University College London.
However, this comes
at a cost, Dr. Dolan says. Things that precede the emotional event tend
to be remembered less well by those who have experienced it.
Dr. Dolan and his
colleagues asked 10 volunteers to study a list of nouns. Each list contained
emotionally aversive words such as "murder" or "scream." The subjects
were then asked to recall the words on the list.
The researchers
found the volunteers remembered the emotionally charged words much better
than the other words. In addition, they had significant trouble remembering
the words that came immediately before the emotionally charged words.
They also found
that among women the effect of emotion-induced amnesia was twice as great
as compared with men, according to their report in the Proceedings
of the National Academy of Sciences.
To determine the
neurological basis for this finding, Dr. Dolan's team repeated the test
with 24 subjects who were given either propranolol, a beta blocker drug
that can also reduce anxiety, or a placebo (an inactive substance).
They also tried
the test on an individual who had damage to the part of the brain called
the amygdala. The amygdala is involved in producing and responding to
nonverbal signs of avoidance, defensiveness, and fear.
The team found that
"by blocking the emotional arousal associated with these events you
can reverse the process," Dr. Dolan says.
Among the subjects
who received the drug and the subject with the damaged amygdala, there
was no improvement in the memory of the emotionally charged words and
no emotional amnesia for the words that came directly before.
Dr. Dolan says the
implication of these findings is that witnesses to emotionally charged
events such as accidents or crimes may have totally incorrect memories
of what led up to the event. Therefore, their accounts may be poor or
unreliable.
Furthering their
research, Dr. Dolan's team continues to study how mechanisms of memory
can be disrupted. Their goal, Dr. Dolan says, is to determine how better
memories are created.
"The findings of
this study are important because they suggest that the brain mechanisms
that we think are important for enhanced memory associated with emotional
events are also involved in memory impairment for emotional events,"
says Dr. Larry Cahill, an assistant professor of neurobiology at the
University of California at Irvine, and author of an accompanying commentary.
"They may lead to
a better understanding of how emotion affects the mechanisms of memory,"
he says.
Always
consult your physician for more information.
Anatomy
of the Brain
The brain can be
divided into the cerebrum, brainstem, and cerebellum:
cerebrum
The cerebrum (supratentorial or front of brain) is composed of the right
and left hemispheres. Functions of the cerebrum include: initiation
of movement, coordination of movement, temperature, touch, vision, hearing,
judgment, reasoning, problem solving, emotions, and learning.
brainstem
The brainstem (midline or middle of brain) includes the midbrain, the
pons, and the medulla. Functions of this area include: movement of the
eyes and mouth, relaying sensory messages (hot, pain, loud, etc.), hunger,
respirations, consciousness, cardiac function, body temperature, involuntary
muscle movements, sneezing, coughing, vomiting, and swallowing.
cerebellum
The cerebellum (infratentorial or back of brain) is located
at the back of the head. Its function is to coordinate voluntary muscle
movements and to maintain posture, balance, and equilibrium.
More specifically,
other parts of the brain include the following:
pons
A deep part of the brain, located in the brainstem, the pons
contains many of the control areas for eye and face movements.
medulla
The lowest part of the brainstem, the medulla is the most vital
part of the entire brain and contains important control centers for
the heart and lungs.
spinal cord
A large bundle of nerve fibers located in the back that extends from
the base of the brain to the lower back, the spinal cord carries messages
to and from the brain and the rest of the body.
frontal
lobe
The largest section of the brain located in the front of the
head, the frontal lobe is involved in personality characteristics and
movement.
parietal
lobe
The middle part of the brain, the parietal lobe helps a person
to identify objects and understand spatial relationships (where one's
body is compared to objects around the person). The parietal lobe is
also involved in interpreting pain and touch in the body.
occipital
lobe
The occipital lobe is the back part of the brain that is involved
with vision.
temporal
lobe
The sides of the brain, these temporal lobes are involved in memory,
speech, and sense of smell.
Online
Resources
Alzheimer's
Disease Association
American
Parkinson Disease Association
Centers
for Disease Control and Prevention (CDC)
Huntington's
Disease Society of America
National
Institutes of Health (NIH)
National
Institute of Mental Health
National
Institute of Neurological Disorders and Stroke
Science
of Emotion, National Institute of Mental Health
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December 2003
In
This Issue:
Emotion
Affects Ability To Recall Events
Anatomy
of the Brain
Experts
Study Neurons and How the Brain Adapts
Medical
Conditions and Neurons
Online
Resources
Other
Resources:
Find
a St. John's Mercy Physician
St.
John's Mercy Center for New Health Options
Mental
Health Information
St.
John's Mercy Classes and Programs
Experts Study Neurons and How the Brain Adapts
A "reset switch"
that increases or decreases the sensitivity of brain cells to
stimulation by their neighbors has been identified by Duke University
Medical Center neurobiologists.
This
action, called homeostatic plasticity, enables the brain to adapt
to changes in the environment. It helps the brain avoid having
its neurons swamped by increased activity of the neural pathway
or from becoming too insensitive to detect triggering impulses
from other neurons when there is low neural activity.
Neurons
are nerve cells that act as information messengers between the
different areas of the brain and the brain and the rest of the
nervous system.
The
Duke scientists, reporting in the medical journal Neuron,
used an array of analytical techniques in their study. They say
this homeostatic plasticity is distinct from more rapid changes
in neural circuits that occur during the formation of memory.
The
research offers long-sought clues to how neurons protect themselves
during stroke, epilepsy, and spinal cord damage. The study may
also help explain various brain changes that occur during early
childhood and problems that occur later in life when people develop
Alzheimer's or Parkinson's disease.
"Neurobiologists
have understood that a neuron can increase only so much its firing
rate in response to inputs from other neurons, and then it saturates," says
lead researcher Dr. Michael Ehlers, an assistant professor of
neurobiology.
"There
had to be a way for a neuron to recalibrate - to scale up or down
to stay within an optimal dynamic firing frequency range," he
says.
"Consider
when you're driving a car with a manual transmission," Dr. Ehlers
says. "As you accelerate, you reach a point where the engine's
RPMs are maximal and can go no higher. At that point, you need
to switch gears to bring back your RPMs to an optimal range.
"What
we have found is the molecular clutch that allows neurons to shift
gears," Dr. Ehlers says. "This really is a profoundly important
discovery. Imagine if your brain could operate only in 'second
gear."
Always
consult your physician for more information.
Medical
Conditions and Neurons
Neurons
are the longest living cells in the body. However, some diseases
of the brain are the result of the unnatural deaths of neurons.
According
to the National Institute of Neurological Disorders and
Stroke:
- In Parkinson’s
disease, neurons that produce the neurotransmitter dopamine
die off in the basal ganglia, an area of the brain that controls
body movements. The basal ganglia is a collection of thousands
of neurons located deep within the brain that controls voluntary
body movement and establishes postures. The brain can no longer
control the body and people shake and jerk in spasms.
- In Huntington’s
disease, a genetic mutation causes over-production of a neurotransmitter
called glutamate, which kills neurons in the basal ganglia.
As a result, people twist and writhe uncontrollably.
- In Alzheimer’s
disease, unusual proteins build up in and around neurons in
the neocortex and hippocampus, parts of the brain that control
memory. When these neurons die, people lose their capacity
to remember and their ability to do everyday tasks. Physical
damage to the brain and other parts of the central nervous
system can also kill or disable neurons.
- Blows
to the brain, or the damage caused by a stroke, can kill neurons
outright or slowly starve them of the oxygen and nutrients
they need to survive.
- Spinal
cord injury can disrupt communication between the brain and
muscles when neurons lose their connection to axons located
below the site of injury. These neurons may still live, but
they lose their ability to communicate.
Always
consult your physician for more information.
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