In detail

Anatomy of fear: what it is, what it is for and how it is generated

Anatomy of fear: what it is, what it is for and how it is generated

Fear is a reaction that is generated in the brain and that begins with a stressful stimulus and ends with the release of chemicals that cause the heart to accelerate, breathing faster and increase the energy of the muscles, in addition to other things, and this process is known as fight or flight response. The stimulus generated by fear could be a spider, an auditorium full of people waiting for us to speak, a vase that falls loudly or a tiger that seems to come to attack us.


  • 1 The brain and fear
  • 2 How do we generate fear? Fear biology
  • 3 Why do we generate fear?
  • 4 The most common fears and their origins

The brain and fear

The brain is a deeply complex organ. It has more than 100 billion nerve cells or neurons that comprise an intricate network of communications and are the starting point for everything we feel, think and do. Some of these communications lead to conscious thought and action, while others produce autonomic responses. The fear response is almost completely autonomous: We are not fully aware of what happens until chemical and physiological responses have begun.

Since cells in the brain are constantly transferring information and triggering responses, there are at least a dozen areas of the brain that are somehow involved in fear. But research has discovered that certain parts of the brain play a more important role in the process, and are the following:

  • Thalamus: decide where to send the sensory data that enters us through the eyes, ears, mouth, skin ...
  • Sensory cortex: Interpret sensory data.
  • The hippocampus: store and retrieve conscious memories, process stimulus sets to establish context.
  • The amygdala: decode emotions, determine possible threat and look in our memories if we should be afraid.
  • The hypothalamus: Activate the "fight or flight" response.

So, it all starts with a stimulus that causes us fear and ends with the fight or flight response.

How do we generate fear? Fear biology

The place where we generate fear is the brain and as we know it is an unconscious process. But there are two ways involved in the fear response: the first way is fast, almost instantaneous and messy, while the second one takes longer and offers a more accurate interpretation of events. Both processes occur almost simultaneously.

The first route is the most unconscious and we are not able to control it at all, the second one instead has an objective, which is "not to take risks." Imagine that suddenly you hear loud knocks on a window of your house, it could be the wind, but it could also be a thief trying to enter. It is much less dangerous to assume that it is the wind than to think that it may be a thief. The first track shoots first and asks later. The process is the following:

The knocks on the window are the stimulus. As soon as we hear the sound, the brain sends this sensory data to the thalamus. At this point, the thalamus does not know if the signals it is receiving are danger signals or not, but since they could be something of concern, Forward the information to the amygdala. The tonsil receives the neuronal impulses and takes measures to protect itself: so tell the hypothalamus to start the fight or flight response that could save your life if what you are hearing turns out to be an intruder.

The second way is much more thoughtful. While the first route is initiating the fear response just in case, the other is considering all options. Is it a thief, or is it the wind? The long process is as follows:

When your ears detect the sound, they transmit this information to the thalamus. The thalamus sends this information to the sensory cortex, where it is interpreted and gives meaning. The sensory cortex determines that there is more than one possible interpretation of the data and it is go to the hippocampus to set the context. The hippocampus asks questions like: "Have I felt this particular stimulus before? If so, what did it mean at this time? What other things are happening that could give me clues about whether it is a thief or a windstorm? " The hippocampus could then collect other data such as the knocking of some branches against the window, an outer thud howl or the noise of an object flying. Taking into account this other information, the hippocampus determines that the blows are most likely the result of the wind. A message is sent to the tonsil that there is no danger, and the tonsil in turn tells the hypothalamus to stop the fight or flight response.

That is why we have a few moments of terror before we can calm down.

Regardless of which path we are talking about, they all lead to the hypothalamus. If it were necessary to produce the fight or flight response, it would be the hypothalamus who would in turn activate two systems: the sympathetic nervous system and the adrenal-cortical system. The sympathetic nervous system uses the 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.

The sympathetic nervous system sends impulses to the glands and smooth muscles and tells the adrenal medulla to release epinephrine (adrenaline) and norepinephrine (norepinephrine) in the bloodstream. These "stress hormones" cause various changes in the body, including an increase in heart rate and blood pressure.

At the same time, the hypothalamus releases corticotropin (CRF) in the pituitary gland, which activates the adrenal-cortical system. The pituitary gland (an important endocrine gland) secretes the hormone ACTH (adrenocorticotropic hormone). ACTH moves through the bloodstream and finally reaches the adrenal cortex, where it activates the release of approximately 30 different hormones that prepare the body to face a threat.

Sudden flooding of epinephrine, norepinephrine and other hormones causes changes in the body that include:

  • Increased heart rate and blood pressure
  • Pupillary dilation
  • The skin veins contract to send more blood to the major muscle groups (responsible for the "coldness" sometimes associated with fear)
  • Increase in blood glucose level
  • Muscles tense, energized by adrenaline and glucose
  • Smooth muscle relaxation in order to provide more oxygen to the lungs
  • Non-essential systems (such as digestion and the immune system) close to allow more energy to emergency functions
  • There are problems concentrating on small tasks (the brain focuses only on "important" things in order to determine where the threat comes from)

All these physical responses are intended to help survive a dangerous situation.

Why do we generate fear?

If we could not generate fear, we could not survive for long. We could run to the road, walk on the roof or approach poisonous snakes without doing anything to avoid it or try to protect ourselves. In both humans and animals, the effects of fear promote survival. Throughout evolution, genes have transmitted the fear trait and the response that is activated as something beneficial for life.

Currently most of us are no longer fighting or running to keep us alive as in nature, but fear is far from being an obsolete instinct. It still serves the same purpose today as it did when it saved us from being eaten by a lion. The difference is that now we walk through the streets of the city. But the decision not to take that shortcut through the deserted alley at midnight is based on a rational fear that promotes survival. What happens is that the stimuli have changed, but we are in danger as much today as we were hundreds of years ago, and fear serves to protect us now as it did then.

Most of us have never been in front of a plague, but our heart jumps when we see a rat. And it is that for human beings there are other factors that intervene in fear beyond one's instinct. Human beings have the ability to anticipate, and we anticipate terrible things that could happen, things we have heard, read or seen. on television Most of us have never experienced a plane crash accident, but that does not prevent us from holding on tight to the seat when it is going to take off. What happens is that anticipating a fear stimulus can provoke the same response as experiencing it in reality, hence there are panic attacks or anxiety attacks, which are anticipatory fear responses and most of the time without real basis.

The most common fears and their origins

A survey conducted in 2005 reveals the most common fears of people in the United States. The list of the first 10 is as follows:

  1. Terrorist attacks
  2. Spiders
  3. Death
  4. Failure
  5. War
  6. Heights
  7. Crime / violence
  8. Being alone
  9. The future
  10. Nuclear war

Most of these basic fears appear in adulthood, although they may already be present in childhood. Other common fears are public speaking, going to the dentist, pain, cancer and snakes.. Many of us are afraid of the same things, so we can say that there are certain fears that are "universal."

Some studies show that humans may be genetically predisposed to fear certain harmful things like spiders, snakes and rats, animals that were once real dangers to humans because they were poisonous or brought diseases. The fear of snakes, for example, has been found in people who have never been in the presence of a snake. This makes sense if you think of fear as an evolutionary instinct embedded in human consciousness.

The psychologist Martin Seligman conducted a classic conditioning experiment in which images of certain objects were shown followed by an electric shock. The idea was to create a phobia (irrational fear) towards the object shown in the image. When the image was of something similar to a spider or a snake, in just two to four downloads the phobia was established. When the image was of something like a flower or a tree, much more was needed to get a real fear.

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 assaulted than someone who has spent most of his life on a farm. There is a phobia called Taijin kyofusho, which is considered a "culturally distinctive phobia of Japan." The Taijin kyofusho is "the fear of offending other people for an excess of modesty or show of respect." The complex social rituals that are part of life in Japan have given rise to a specific Japanese fear.

Experiencing fear from time to time is a normal part of life. But living with chronic fear can be both physically and emotionally debilitating. Living with a deteriorated immune response and high blood pressure causes illness, as well as refusing to participate in daily activities out of fear, brings a life of sadness and loss of value. So if you are one of those who fear prevents you from living a normal life, it is important that you go to a specialist to help you.