Cerebro y fobias - Phobias and the brain

Phobias and the brain

A phobia is an intense fear that appears immediately when faced with a specific object or situation. Most common phobias include fear of certain animals or insects, flying, heights, injections or blood. However, phobic situations and objects can vary greatly.

Fear should help protect us; with a phobia though, the fear is maladaptive and can become an obstacle in our daily routine. Phobias are learned just like any other fear and are accompanied by plastic changes in the brain that occur very quickly and are very resistant to extinction, as the body feels that its very survival would be at stake if the fear ceased.

The brain structure that plays a critical role in phobias is the amygdala that is commonly associated with emotions (especially fear). The amygdala is responsible for connecting the fear-arousing stimulus with theenvironmental contextin which it is occurring. In addition, the amygdala triggers responses from the body to react quickly to threat and danger.

How to tell if you have a phobia

According to the diagnostic criteria of the 5th edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), the features of phobias are described below:

  • The phobic object or situation is actively avoided. Individuals refuse to stay in the feared situation, something that can lead to a deterioration in quality of life, especially if the phobic stimulus is encountered on a day-to-day basis.
  • The fear or anxiety is persistent, usually lasting for 6 months or more.
  • Individuals with specific phobia recognize that their anxietyis out of proportion to the actual danger that the object or situation poses.
  • Fear, anxiety or avoidance can cause significant distress or affect areas of functioning (e.g., social life, work).


 

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The origins of phobia. Brain-phobia connectivity

Fear and anxiety have a biological basis, that is, they are evolutionarily developed responses aimed at detecting or anticipating threats. Fear is accompanied by autonomic and endocrine changes that prepare the body to react to danger (e.g., fighting, fleeing, or freezing) with the aim of increasing chances of survival.

However, this fear can be maladaptive (as in the case of phobias) because, in addition to not contributing significantly to survival, it can create difficulties in our daily lives.

Organisms have innate fears, that is, they are born with these fears,they didn’t have to learn them through experience. Examples of innate fears are painful or very intense stimuli such as loud sounds. However, as individuals gain worldly experience, they become aware of the existence of aversive and dangerous situations. Little by little, they learn what they are and where they usually appear to avoid them or deal with them efficiently. This learned fear is still adaptive, but it can become maladaptive as in phobias and anxiety disorders.

Pavlovian conditioning

Pavlovian conditioning is one of the most commonly used models of fear learning: here, a neutral stimulus (e.g., a tone) is paired with an aversive event (e.g., an electric shock); the conditioned stimulus, which at first meant nothing, acquires an ability to elicit fear in the subject. This happens because the tone-shock pairing is quickly stored in memory, and the fear response is displayed as soon as the tone is heard.

Theory of biological preparedness

Fear conditioning is a powerful process that occurs very quickly. A single pairing of two such stimuli is sufficient to establish a memory.

According to Martin Seligman’s theory of biological preparedness, phobias result from a group of biological associations that the organism is evolutionarily prepared to learn quickly and persistently. Thus, conditioning to fear-relevant stimuli such as snakes, spiders, fearful or angry facial expressions and out-groupfaces are more resistant to extinction and can be consolidated without conscious awareness.

Once learned, conditioned fear responses can last a lifetime. However, fear responses may weaken or extinguish through experiences that show that the conditioned stimulus no longer predicts danger.

Neural basis

The entire process of acquiring phobias has a neural basis. The brain is plastic, that is, it changes based on habits and learning. During fear conditioning, neurons undergo molecular and structural changes.

In addition, there are also specific brain regions that are closely associated withfear and phobias. The region most relevant is the amygdala, whose role is described below.

Amygdala and phobias

The amygdala is typically associated with both adaptive and maladaptive fear. It is a small almond-like shape structure located deep in the brain that is part of the limbic system (system for emotion).

The amygdala is a complex structure consisting of several distinct groups of cells, interconnected and functionally diverse:

  • The lateral nucleus of the amygdala receives inputs from all sensory modalities (visual, auditory, tactile, etc.) and is responsible for linking information with the noxiousstimulus. In addition, studies have revealed that this information reaches the lateral amygdala through “two roads” or two distinct sensory inputs. The first, the thalamic pathway, is shorter and provides information rapidly but in an imprecise manner. The second, the cortical pathway, delivers more complex, refined, and conscious representation of the external stimulus.

The lateral amygdala is the main site of synaptic changes under lying fear learning. Neural connections become strengthened as fear conditioning is established.

  • The central nucleus of the amygdala is responsible for sending processed information to brain stem regions and controls expression of fear responses such as freezing. It also activates the adrenergic, serotonergic, dopaminergic and cholinergic systems that cause endocrine and autonomic changes typical of fear.
  • The basal nucleus of the amygdala receives inputs from the hippocampus and enthorhinal and polymodal associative cortices. Have you noticed that you can feel fear in a place where the phobic stimulus appeared in the past, even if it is not present now? This happens because this site of the amygdala stores information relating to the environmental context in which the threat occurred.
  • The intercalatedcells area subgroup of GABAergic neurons that have inhibitory control. They can inhibit fear responses by “blocking” the information from the lateral and basal nuclei to the central nucleus (e.g., in the event of a false alarm).

 

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Interesting studies on phobias and brain activity

Animal studies have shown that if the central nucleus of the amygdala is stimulated, different parts of the fear response can be triggered. However, damage to this site decreases fear responses to conditioned stimuli. Furthermore, the person cannot acquirenew fears.

On the other hand, damage tothe hippocampus—an area that sends input to the amygdala regarding the location of the fear-arousing stimulus—onlyeliminates the contextual fear conditioningwithout affecting conditioned fear to the stimulus.

Regarding brain activity in phobias, a study by Schienleet al. (2005) found differences between individuals with spider phobia and those who did not suffer from spider phobia while viewing pictures of spiders and other pictures of neutral insects. Spider phobics showed greater activation of the amygdalae, the visual association cortex, the right hippocampus, and the right dorsolateral prefrontal cortex. This latter area appears to be associated with the processing of negative emotions. Activation was also observed in the supplementary motor area (which is involved in movement preparation and motivation). In addition, spider phobic individuals showed greater amygdala activation than control subjects while viewing the disgust-inducing pictures.

A meta-analysis published in 2012 showed hyperactivation in the insula (as well as in the amygdala) of phobic individuals. Both structures are associated with negative emotional responses.

Eliminating phobias

How to make phobias disappear? Phobias may be eliminated by repeated exposure to the fear-arousing stimulus in a neutral or safe context. Little by little, the person learns that the phobic object or event is no longer dangerous. This phenomenonforms a basis of effective exposure therapies.

There is neural basis for all this too, since studies have revealed that interactions between the amygdala, the hippocampus and the medial prefrontal cortex regulate the extinction of fear.

References

  • Asociación Americana de Psiquiatría. (2013). Guía de consulta de los criterios diagnósticos del DSM-5.
  • Dbiec, J., &LeDoux, J. (2009). Theamygdala and the neural pathwaysoffear. In Post-Traumatic Stress Disorder (pp. 23-38). Humana Press.
  • Etkin, A., &Wager, T. D. (2007). Functional Neuroimaging of Anxiety: A Meta-Analysis of Emotional Processing in PTSD, Social AnxietyDisorder, and SpecificPhobia. The American Journal of Psychiatry, 164(10), 1476–1488. http://doi.org/10.1176/appi.ajp.2007.07030504
  • LaBar, K. S., & Cabeza, R. (2006). Cognitiveneuroscienceofemotionalmemory. Nature Reviews Neuroscience, 7(1), 54.
  • Sánchez Navarro, J. P., & Román, F. (2004). Amígdala, corteza prefrontal y especialización hemisférica en la experiencia y expresión emocional. Anales de psicología, 20(2).
  • Schienle, A., Schäfer, A., Walter, B., Stark, R., &Vaitl, D. (2005). Brain activation of spider phobics towards disorder-relevant, generally disgust-and fear-inducing pictures. Neuroscience Letters, 388(1), 1-6.

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Cinta Martos

Licenciada en Psicología (Universidad de Huelva) y Máster en Cerebro y Conducta con especialidad en Neuropsicología Clínica (Universidad de Sevilla).

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