The Brain and Fear: Neurobiological and Neuropsychological Foundations
What Happens in the Brain When We Are Afraid?
What occurs in the brain’s structure when a person is frightened? Which brain regions are responsible for fear? According to researchers, understanding these processes can help treat many mental and physiological disorders.
The Evolutionary Significance of Fear
Fear is the most basic and fundamental instinct. It is one of the oldest reactions living organisms have to danger and is key to evolutionary development. Fear has allowed many species, including Homo sapiens, to survive and evolve.
Whether it’s a mouse, a monkey, or a human, the ability to survive numerous threats in the environment depends on appropriate defensive behavior. It’s important not only to quickly detect and respond to imminent dangers but also to anticipate when and where threats may arise. Fear regulates innate or learned defensive reactions-“fight,” “flight,” or “freeze.”
This is one of the few emotions that manifests almost identically across all members of the animal kingdom, including humans. Moreover, fear is the fastest and most powerful instinct, surpassing all other emotions in intensity.
According to scientists, psychologists, and neurophysiologists, our psyche processes and interprets fear in a highly complex way. Of all animals, humans have the greatest number of fears, including subjective and irrational ones (phobias) that exist only in our imagination and have no real basis.
Fear can be described by various terms depending on its intensity: anxiety, apprehension, fright, fear, terror, phobia, paranoia, persecution complex, and so on.
The Role of the Prefrontal Cortex and Amygdala
Modern research has greatly advanced our understanding of the neural basis of fear and identified common patterns involved in its regulation.
“We have made significant progress in research; now we need to systematize the knowledge we’ve gained,” says Professor of Neuropsychology Stephen Maren, one of the leading experts in the field. “Today, we use both behavioral and systemic neurobiology methods to understand the brain processes of fear and anxiety. These approaches include reversible brain lesions, intracranial pharmacology, and electrophysiology.”
Specifically, it has been established that the amygdala, hippocampus, and medial prefrontal cortex play key roles in managing fear responses.
The hippocampus, amygdala, and prefrontal cortex form a triad of interconnected brain regions responsible for the mechanisms of fear and anxiety.
The Amygdala
The amygdala is a structure in the temporal lobe of the brain that is crucial for the emergence of negative emotions, especially fear. Studies on rats, mice, rabbits, primates, and humans show that the amygdala’s nuclei are involved in both innate and learned fears.
A threat signal, such as the sight of an approaching predator, triggers a fear response in the amygdala. It activates areas involved in preparing for motor functions related to fighting or fleeing. This leads to the release of stress hormones and activation of the sympathetic nervous system.
These changes prepare us for danger: brain activity increases, pupils dilate, bronchi expand, and breathing quickens. Heart rate and blood pressure rise. Blood and glucose flow to skeletal muscles increases. The function of organs not essential for immediate survival, such as the digestive system, slows down.
The Hippocampus and Prefrontal Cortex
The hippocampus and prefrontal cortex help the brain interpret perceived threats. They process higher-level contextual information, helping a person determine whether a perceived threat is real.
For example, seeing a lion or bear in the wild may trigger a strong fear response, but seeing them in a zoo is more likely to evoke curiosity and the thought that they are cute and amusing animals.
This is because the hippocampus and prefrontal cortex process contextual information, and inhibitory pathways dampen the amygdala’s response. Essentially, our “thinking” brain convinces our “emotional” brain that we are actually safe.
The Two-System Concept of Fear and Anxiety
According to scientists, the development of fear is determined by two neural pathways that ideally function simultaneously.
In his book “Anxiety: The Modern Mind in an Age of Anxiety,” renowned neuroscientist Joseph E. LeDoux divides the emotional brain into two parts: an evolutionarily older threat-detection system centered in the amygdala, and a newer system underlying the conscious feeling of fear, mainly located in the prefrontal cortex.
The first system, responsible for basic emotions, reacts quickly but is prone to many errors. The second system responds more slowly but with greater accuracy.
While the first system operates mostly unconsciously, the second generates conscious feelings and experiences.
The first pathway allows a person to respond rapidly to signs of danger but often triggers false alarms. The second pathway enables a more accurate assessment of the situation and a more precise response to danger. In this case, the feeling of fear initiated by the first pathway is blocked by the functioning of the second, which evaluates certain danger signals as not real.
In the first pathway (low, short, subcortical), an emotional stimulus is relayed from the sensory nuclei of the thalamus directly to the amygdala, causing an emotional response.
In the second pathway (high, long, cortical), the emotional stimulus is relayed from the sensory nuclei of the thalamus to the sensory areas of the cerebral cortex and then to the amygdala, forming an emotional response.
Neurobiological Brain Response to Fear
Joseph LeDoux argues that while the amygdala detects and responds to danger, it is not, as commonly believed, the “center of fear,” since it is not solely responsible for the conscious feeling of fear. His conclusion is supported by studies showing that although damage to the amygdala in humans eliminates threat responses, it does not prevent people from feeling fear.
Subjective experiences of fear and other emotions, such as anxiety, are processed by higher-order brain networks, mainly involving the prefrontal cortex. These networks underlie cognitive processes such as attention, working memory, and decision-making. Neural connections within these networks allow you to recognize threats based on past experiences (memories), label your state with words, and consciously experience fear-that is, to feel that your well-being is under threat.
Numerous phobias that develop in mental disorders result from inadequate functioning of the second pathway. In these cases, the second system malfunctions, leading to fear responses to stimuli that are not actually dangerous. Such pathologies cause people to fear things that do not exist in reality. Examples include ablutophobia (fear of washing and bathing), ambulophobia (fear of walking), or the even more unusual arachibutyrophobia (fear of peanut butter sticking to the roof of the mouth).
Since the inability to adaptively regulate fear and defensive behavior is a central component of many anxiety disorders, the brain mechanisms that provide flexible responses to threats are of great clinical importance. Understanding the roles of the prefrontal cortex and amygdala in the emergence of fear will lead to progress in developing treatments for fear and anxiety disorders in humans.