Tiny Structure in Brain May Be Key to Recognizing Fear : Science: Researchers say the amygdala helps read social signals and links the mental and the physical.
Is any text on human affairs so closely read as the faces of the men and women around us? The vocabulary is unmistakable: the pursed lips of distaste, the widened eyes of fear, the wrinkled nose of disgust.
To live without the ability to read such facial expressions is to be illiterate in an almost universal, unspoken language of emotion.
Now scientists have discovered “rare and remarkable” evidence that an almond-sized structure hidden deep within the human brain may be the key to recognizing the play of emotions in facial expressions.
Damage it and a person can no longer recognize fear in another’s face.
“It is one of the most significant observations in the history of the study of facial expressions,” said Caltech neurobiologist John Allman.
The provocative finding, made public Wednesday, adds to a growing storehouse of tantalizing insights into the neurobiology of emotions. It hints at how a critical juncture in the brain serves as an intermediary between the mind’s intangible intellectual activity and the body’s more physical responses.
Authorities said it also is evidence that the mind’s emotions evolved in tandem with the body because fear--so crucial to the functioning and survival of human beings--apparently occupies a distinct physical place in the brain, separate from the seat of any positive emotions.
In research published today in the journal Nature, scientists at the Salk Institute in La Jolla and the University of Iowa College of Medicine have discovered that a part of the brain called the amygdala plays a central role in discerning human social signals. The organ is located near the base of the brain’s gelatinous, three-pound sponge of tissue.
The team reached its conclusions by studying an unusual patient--”a case in a million”--in whom the amygdala cells had been destroyed by disease.
Without the cluster of special neural cells, human beings apparently cannot recognize fear, nor can they decipher the suite of emotions in more complex facial expressions, the researchers said. But they have no trouble recognizing to whom a face belongs.
What the researchers found most striking was that no positive emotions were affected. In this instance, the patient could not perceive fear in another’s expression, yet had no trouble recognizing the broad smile and crinkled eyes of happiness.
“The patient looks at a face of fear and she has no idea what she is seeing,” he said. “She can recognize happiness perfectly.”
She was asked to rate pictures of faces showing expressions of half a dozen basic emotions and put through a variety of standard mental evaluation tests.
“This information is extremely important for our understanding of social behavior in general,” said Antonio R. Damasio, the neurologist who led the research team. “What is at stake here is how we utilize a language not made up of words or signs to communicate meaning to others.”
For centuries, philosophers and scientists have puzzled over the relationship between the mind and the millions of neural cells that make up the brain. Researchers have tried to decipher how the brain creates mental experience by studying monkeys, rats, snails and--indirectly with computerized imaging techniques or brain-wave measurements--human volunteers.
Earlier studies with laboratory animals had convinced researchers that the tiny organ is crucial to the formation of emotional memories and fear responses. In a long series of experiments with laboratory animals, Dr. John L. McGaugh at the UC Irvine Center for the Neurobiology of Learning and Memory pinpointed the amygdala as the site where adrenaline and other hormones affect memory.
Using advanced computerized imaging techniques, other researchers have observed the way blood flows and pools in brains of human volunteers and determined that the organ also plays a central role in the onset of clinical depression. It even appears to cement recollection of charged events more firmly in the mind, by linking emotions to long-term memories.
But until now, researchers had no direct way to plumb its function in the human brain.
“It opens the door to a different view of the brain,” said Dr. Leslie Brothers, a UCLA research psychiatrist at West Los Angeles Veterans Administration Medical Center who researches the role of the amygdala in non-human primates. “I was thrilled. This makes it very clear that the amygdala is involved in receiving social signals in humans.”
Several researchers cautioned that because the report concerns a test of impaired brain function in a single person, the results may not be widely applicable. But other scientists said the finding fits neatly into a broad pattern of research results from animal experiments and tests of human patients with brain defects.
“It is consistent with lots of other emerging findings,” McGaugh said. “The basic premise is a strong one and is going to gain ever-increasing support.”
In research that has not yet been published, for example, Damasio’s group has tested a second patient with more severe neurological damage centered in the amygdala. He has lost the ability to recognize fear and anger in others, Allman said.
A third patient, with less severe damage to the amygdala, is no longer able to tell in what direction someone is gazing. “She literally could not tell whether someone was looking at her or not,” Allman said.
“It would make normal social discourse very impaired. If you can’t make eye contact with a person, it makes you very uncomfortable,” he said.
Damasio and several other scientists believe the research offers important evidence that the mind and the body evolved together, with primary emotions such as fear becoming a separate and integral part of the brain because they play such an important role in survival. The amygdala is tightly connected to other parts of the brain responsible for the “fight-or-flight” reflexes that are probably older than the human species itself.
“Not all emotions have the same value,” Damasio said. “It is quite likely that emotions such as fear have a much higher adaptive value because it can signal a situation of danger. It has been segregated, selected and developed apart from others. This is the clue that neurobiology is giving us.
“An emotion is not a luxury. It is something vital for our survival because it is part and parcel of how we guide our behavior and reason,” he said. “This is woven into the fabric of our biology.”
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Mind and Emotion
* The Discovery:
When a part of the human brain called the amygdala is destroyed, a person no longer can recognize common emotions in facial expressions, especially fear.
* What It Means:
It demonstrates how the brain acts as a broker between intangible activities of the mind and physical responses, suggesting that primary emotions are an integral part of the brain’s neural circuits.
