Fear is a strange aspect that a lot of humans have to contend with each day of their lives. Some people have debilitating fears or ‘phobias’ where as the mass majority can normally over come these fears, but still have them. Phobias will be covered further down but first I think it a good idea if we cover exactly what fear is.
What is Fear?
Fear is a chain reaction in the brain that starts with a stressful stimulus and ends with the release of chemicals that cause a racing heart, fast breathing and energized muscles, among other things, also known as the fight-or-flight response. The stimulus could be a spider, a knife at your throat, an auditorium full of people waiting for you to speak or the sudden thud of your front door against the door frame.
 ÂThe brain is a profoundly complex organ. More than 100 billion nerve cells comprise an intricate network of communications that is the starting point of everything we sense, think and do. Some of these communications lead to conscious thought and action, while others produce autonomic responses. The fear response is almost entirely autonomic: We don’t consciously trigger it or even know what’s going on until it has run its course.
Because cells in the brain are constantly transferring information and triggering responses, there are dozens of areas of the brain at least peripherally involved in fear. But research has discovered that certain parts of the brain play central roles in the process.
> Thalamus - decides where to send incoming sensory data (from eyes, ears, mouth, skin)
> Sensory cortex – interprets sensory data
> Hippocampus – stores and retrieves conscious memories; processes sets of stimuli to establish context
> Amygdala - decodes emotions; determines possible threat; stores fear memories
> Hypothalamus - activates “fight or flight” response
TÂhe process of creating fear begins with a scary stimulus and ends with the fight-or-flight response. But there are at least two paths between the start and the end of the process. In the next section, we’ll take a closer look at how fear is created.
How is Fear Created and the Path of Fear in your brain
The process of creating fear takes place in the brain and is entirely unconscious. There are two paths involved in the fear response: The low road is quick and messy, while the high road takes more time and delivers a more precise interpretation of events. Both processes are happening simultaneously.
The idea behind the low road is “take no chances.” If the front door to your home is suddenly knocking against the frame, it could be the wind. It could also be a burglar trying to get in. It’s far less dangerous to assume it’s a burglar and have it turn out to be the wind than to assume it’s the wind and have it turn out to be a burglar. The low road shoots first and asks questions later. The process looks like this:
The door knocking against the door frame is the stimulus. As soon as you hear the sound and see the motion, your brain sends this sensory data to the thalamus. At this point, the thalamus doesn’t know if the signals it’s receiving are signs of danger or not, but since they might be, it forwards the information to the amygdala. The amygdala receives the neural impulses and takes action to protect you: It tells the hypothalamus to initiate the fight-or-flight response that could save your life if what you’re seeing and hearing turns out to be an intruder.
The high road is much more thoughtful. While the low road is initiating the fear response just in case, the high road is considering all of the options. Is it a burglar, or is it the wind? The long process looks like this:
When your eyes and ears sense the sound and motion of the door, they relay this information to the thalamus. The thalamus sends this information to the sensory cortex, where it is interpreted for meaning. The sensory cortex determines that there is more than one possible interpretation of the data and passes it along to the hippocampus to establish context. The hippocampus asks questions like, “Have I seen this particular stimulus before? If so, what did it mean that time? What other things are going on that might give me clues as to whether this is a burglar or a wind storm?” The hippocampus might pick up on other data being relayed through the high road, like the tapping of branches against a window, a muffled howling sound outside and the clatter of patio furniture flying about. Taking into account this other information, the hippocampus determines that the door action is most likely the result of wind. It sends a message to the amygdala that there is no danger, and the amygdala in turn tells the hypothalamus to shut off the fight-or-flight response.
The sensory data regarding the door — the stimulus — is following both paths at the same time. But the high road takes longer than the low road. That’s why you have a moment or two of terror before you calm down.
Regardless of which path we’re talking about, all roads lead to the hypothalamus. This portion of the brain controls the ancient survival reaction called the fight-or-flight response. In the next section, we’ll take a closer look at the fight-or-flight response.
Fear and the Fight or Flight Response
To produce the fight-or-flight response, the hypothalamus activates two systems: the sympathetic nervous system and the adrenal-cortical system. The sympathetic nervous system uses nerve pathways to initiate reactions in the body, and the adrenal-cortical system uses the bloodstream. The combined effects of these two systems are the fight-or-flight response.
When the hypothalamus tells the sympathetic nervous system to kick into gear, the overall effect is that the body speeds up, tenses up and becomes generally very alert. If there’s a burglar at the door, you’re going to have to take action — and fast. The sympathetic nervous system sends out impulses to glands and smooth muscles and tells the adrenal medulla to release epinephrine (adrenaline) and norepinephrine (noradrenaline) into the bloodstream. These “stress hormones” cause several changes in the body, including an increase in heart rate and blood pressure.
At the same time, the hypothalamus releases corticotropin-releasing factor (CRF) into the pituitary gland, activating the adrenal-cortical system. The pituitary gland (a major endocrine gland) secretes the hormone ACTH (adrenocorticotropic hormone). ACTH moves through the bloodstream and ultimately arrives at the adrenal cortex, where it activates the release of approximately 30 different hormones that get the body prepared to deal with a threat.
The sudden flood of epinephrine, norepinephrine and dozens of other hormones causes changes in the body that include:
> Heart rate and blood pressure increase.
> Pupils dilate to take in as much light as possible.
> Veins in skin constrict to send more blood to major muscle groups (responsible for the “chill” sometimes associated with fear — less blood in the skin to keep it warm).
> Blood-glucose level increases.
> Muscles tense up, energized by adrenaline and glucose (responsible for goose bumps — when tiny muscles attached to each hair on surface of skin tense up, the hairs are forced upright, pulling skin with them).
> Smooth muscle relaxes in order to allow more oxygen into the lungs.
> Nonessential systems (like digestion and immune system) shut down to allow more energy for emergency functions.
> Trouble focusing on small tasks (brain is directed to focus only on big picture in order to determine where threat is coming from).
ÂAll of these physical responses are intended to help you survive a dangerous situation by preparing you to either run for your life or fight for your life (thus the term “fight or flight”). Fear — and the fight-or-flight response in particular — is an instinct that every animal possesses.
Why Humans Fear
If we couldn’t be afraid, we wouldn’t survive for long. We’d be walking into oncoming traffic, stepping off of rooftops and carelessly handling poisonous snakes. We’d be hanging out with people who have tuberculosis. In humans and in all animals, the purpose of fear is to promote survival. In the course of human evolution, the people who feared the right things survived to pass on their genes. In passing on their genes, the trait of fear and the response to it were selected as beneficial to the race.
During the 19th-century debate surrounding evolution, the “face of fear” — that wide-eyed, gaping grimace that often accompanies sheer terror — became a talking point. Why do people make that face when they’re terrified? Some said God had given people a way to let others know they were afraid even if they didn’t speak the same language. Charles Darwin said it was a result of the instinctive tightening of muscles triggered by an evolved response to fear. To prove his point, he went to the reptile house at the London Zoological Gardens. Trying to remain perfectly calm, he stood as close to the glass as possible while a puff adder lunged toward him on the other side. Every time it happened, he grimaced and jumped back. In his diary, he writes, “My will and reason were powerless against the imagination of a danger which had never been experienced.” He concluded that the entire fear response is an ancient instinct that has been untouched by the nuances of modern civilization [ref].
Most of us are no longer fighting (or running) for our lives in the wild, but fear is far from an outdated instinct. It serves the same purpose today as it did when we might run into a lion while carrying water back from the river. Only now, we’re carrying a wallet and walking down city streets. The decision not to take that shortcut through the deserted alley at midnight is based on a rational fear that promotes survival. Only the stimuli have changed — we’re in as much danger today as we were hundreds of years ago, and our fear serves to protect us now as it did then.
Darwin had never experienced the bite of a poisonous snake, and yet he reacted to it as if his life were in danger. Most of us have never been anywhere near The Plague, but our heart will skip a beat at the sight of a rat. For humans, there are other factors involved in fear beyond instinct. Human beings have the sometimes unfortunate gift of anticipation, and we anticipate terrible things that might happen — things we have heard about, read about or seen on TV. Most of us have never experienced a plane crash, but that doesn’t stop us from sitting on a plane with white-knuckle grips on the armrests. Anticipating a fearful stimulus can provoke the same response as actually experiencing it. This also is an evolutionary benefit: Those humans who felt rain, anticipated lightning and remained in the cave until the storm passed had a better chance of not getting struck with thousands of volts of electricity. We’ll look at ways in which we are conditioned to fear in the next section.
Common Fears in Humans
Some studies show that humans might be genetically predisposed to fear certain harmful things like spiders, snakes and rats — animals that once posed a real danger to human beings because they were poisonous or carried disease. Fear of snakes, for example, has been found in people who have never even been in the presence of a snake. This makes sense if you think about fear as an evolutionary instinct embedded in the human consciousness. This idea of the universal fear is supported by such reputable sources as popular television: NBC’s “Fear Factor” offers a weekly $50,000 prize to the contestant who can perform tasks like sticking his head into a box filled with hundreds of spiders and eating a blended rat smoothie.
The idea is also supported by scientific research. Psychologist Martin Seligman performed a classical conditioning experiment in which he showed subjects pictures of certain objects and then administered an electric shock. The idea was to create a phobia (an intense, irrational fear) of the object in the picture. When the picture was of something like a spider or a snake, it took only two to four shocks to establish a phobia. When the picture was of something like a flower or a tree, it took a lot more shocks to get a real fear going.
But while there may be “universal fears,” there are also fears that are particular to individuals, communities, regions or even cultures. Someone who grew up in the city probably has a more intense fear of being mugged than someone who has spent most of his life on a farm. People living in South Florida may have a stronger fear of hurricanes than people living in Kansas, and people in Kansas probably have a deeper fear of tornadoes than do people in Vermont. What we fear says a lot about our life experience. There is a phobia called taijin kyofusho that is considered in the psychiatric community (according to the DSM IV) to be a “culturally distinctive phobia in Japan.” Taijin kyofusho is “the fear of offending other persons by an excess of modesty or showing respect.” The intricate social rituals that are part of life in Japan have led to a Japanese-specific fear.
Experiencing fear every now and then is a normal part of life. But living with chronic fear can be both physically and emotionally debilitating. Living with an impaired immune response and high blood pressure causes illness, and refusing to participate in daily activities because you might be confronted with heights or social interaction doesn’t make for a very fulfilling life. So what can we do about our fears?
Fear extinction
Whereas Little Albert learned to fear white rats in the 1920s, rats learned to fear a simple noise more than 80 years later. Scientist Mark Barad of UCLA performed an experiment in which he and his team combined a noise with an electric shock. They would play the tone and then immediately apply a shock to the metal floor of the rats’ cage. It was classical conditioning, and it didn’t take long for the rats to brace themselves for the shock as soon as they heard the sound. At that point, their amygdalas paired the sound with the shock, and the sound created a fear response. The researchers then began the process of fear-extinction training, in which they made the sound but did not apply the shock. After hearing the sound very often without the shock, the rats stopped fearing the noise.
Fear extinction involves creating a conditioned response that counters the conditioned fear response. While studies situate the amygdala as the location of fear memories formed by conditioning, scientists theorize that fear-extinction memories form in the amygdala but then are transferred to the medial prefrontal cortex (mPFC) for storage. The new memory created by fear extinction resides in the mPFC and attempts to override the fear memory triggered in the amygdala.
Most behavioral therapies for fear extinction focus on exposure. For instance, therapy for a person with a fear of snakes might involve visiting a snake farm repeatedly and taking small steps toward touching one. First, the person might get within 10 feet of the snake and see that nothing terrible happens. Then he might get within 5 feet of the snake. When nothing terrible happens within 5 feet of the snake, he might get close enough to touch it. This process continues until new, fear-extinction memories are formed — memories that say “snakes are not going to harm you” and serve to contradict the fear of snakes that lives in the amygdala. The fear still exists, but the idea is to override it with the new memory.
Fear-extinction Medication
Scientists have learned that inhibiting a protein called NMDA (N-methyl D-asparate) in the amygdala inhibits fear extinction. They reasoned, then, that stimulating that protein might stimulate fear extinction. Studies show that the antibiotic D-cycloserine (well-known for treating tuberculosis) might be helpful in fear extinction by assisting the action of NMDA [ref]. This type of approach would be beneficial when paired with behavioral therapies that attempt to create fear-extinction memories.
The idea is not to replace exposure therapy, but to speed it up. This hypothesis was played out in a study on rats who’d been conditioned to associate a bright light with a foot shock. When the light was presented repeatedly without the shock, the rats who’d been injected with D-cycloserine unlearned their fear much faster than those who were going the natural route. The antibiotic also achieved results in a study of people with a fear of heights. Following virtual-reality sessions designed to expose individuals to heights in a safe environment, the people who’d been given the antibiotic exposed themselves to heights in the real world twice as often as the subjects who did not receive the drug.
This type of research is very promising for people who are under the control of debilitating phobias and anxiety disorders. But what about those of us who just get butterflies before delivering a presentation or have trouble getting close enough to the thirtieth-floor balcony to check out the view?
New pathway for fear discovered deep within brain
Study by researches find a new neural Circuit that links the site of fear memory with a brain area that controls behaviour
Fear is primal. In the wild, it serves as a protective mechanism, allowing animals to avoid predators or other perceived threats. For humans, fear is much more complex. A normal amount keeps us safe from danger. But in extreme cases, like post-traumatic stress disorder (PTSD), too much fear can prevent people from living healthy, productive lives. Researchers are actively working to understand how the brain translates fear into action. Today, scientists at Cold Spring Harbor Laboratory (CSHL) announce the discovery of a new neural circuit in the brain that directly links the site of fear memory with an area of the brainstem that controls behavior.
How does the brain convert an emotion into a behavioral response? For years, researchers have known that fear memories are learned and stored in a small structure in the brain known as the amygdala. Any disturbing event activates neurons in the lateral and then central portions of the amygdala. The signals are then communicated internally, passing from one group of neurons to the next. From there, they reach neurons in the brainstem, the action center for fear responses.
Last year, CSHL Associate Professor Bo Li and his colleagues were able to use new genetic techniques to determine the precise neurons in the central amygdala that control fear memory. His current research exploits new methods to understand how the central amygdala communicates fear memories to the areas of the brain that are responsible for action.
In work published today in The Journal of Neuroscience, Li and his team identify a group of long-range neurons that extend from the central amygdala. These neurons project to an area of the brainstem, known as the midbrain periaqueductal gray (PAG), that controls the fear response.
Li and his colleagues explored how these long-range neurons participate in fear conditioning. They trained animals to associate a particular sound with a shock, conditioning the animals to fear the sound. In these animals, the activity of the long-range projection neurons in the central amygdala became enhanced.
“This study not only establishes a novel pathway for fear learning, but also identifies neurons that actively participate in fear conditioning,” says Li. “This new pathway can mediate the effect of the central amygdala directly, rather than signaling through other neurons, as traditionally thought.”
The next step for these researchers is to apply this knowledge to models of PTSD. “We are working to find out how these circuits behave in anxiety disorders, so that we can hopefully learn to control fear in diseases such as PTSD,” says Li.
phobias
For a total A to Z list please click here
PDF Documents/Papers On Phobias, Fear and the affects on the Human Brain
> Phobia Information Leaflet
> The Human Brain – Structure and Function of the Brain
> Human Amygdala Activation during Conditioned Fear Acquisition and Extinction
> Emotional Memory Mechanisms in the Human Brain
> Neuronal Circuits of Fear Extinction
> Neurobiology of Emotion
> Fear – Brain and the Amygdala
> Understanding Phobias
> Phobia Types
Documentary on Fear
The Science and Psychology behind Fear
How Stuff Works: Fear
Study Shows Brains Response to Scary Stimuli
Fight or Flight Response
– Credit and Resources –
What is Fear? and How it Affect Humans
No comments:
Post a Comment