Phobias and Brain Activity

October 26, 2016
Heidi Moawad, MD

Phobias are associated with major alterations in brain activity as detected by functional imaging studies.

Phobias are irrational and persistent fears focused on certain objects in the environment, typically livings things. Common phobias include spiders, snakes, birds, clowns, bridges, and blood. Strangely enough, people do not generally have many different phobia triggers. For example, a person who suffers from a phobia of spiders might not have the same reaction to snakes and a person who has a phobia of clowns might not fear bridges.

Phobias are object specific, and they do tend to focus on things that are generally considered moderately, if not profoundly, unpleasant, even for those who do not have phobias. There are a few curious exceptions in which some stereotypical phobia triggers are not widely considered to be unpleasant. For example, clown phobia is fairly common and, at the same time, clowns are generally considered to be entertaining characters. Perhaps it is the makeup-induced obscuration of normal facial features that makes clowns appear as odd or misshaped humans, triggering a severe reaction among those who suffer from clown phobias. Birds, similarly, may provoke an immobilizing fear that is beyond cognitive reasoning among people who suffer from this phobia.

And, interestingly, phobias are not well explained by early life trauma. In fact, many people who have had unpleasant encounters with phobia-inducing creatures do not go on to develop phobias.

Phobias and the brain 

It turns out that phobias are associated with major alterations in brain activity as detected by functional imaging studies. Individuals who suffer from phobias have been shown to display increased activity of the amygdala when exposed to phobia-inducing stimuli, noted on functional MRI. The amygdala is known to be associated with emotional reactions. One observation is that the right amygdala is more highly reactive in response to negative emotions, such as those associated with phobias, while the left amygdala is more strongly associated with pleasant emotional reactions. Interestingly, one study suggested that the higher the activation of the right amygdala, the greater the sense of distress induced by the phobia trigger.

The stria terminalis, the anterior cingulate cortex, and the insula were found to be hyperactivated in individuals who experienced sustained exposure to phobia-inducing pictures in an experimental setting. This suggests that prolonged exposure to phobia-inducing stimuli does not necessarily 'quiet down' brain activity as would be expected, but actually engages more areas of the brain.

Anticipation and imagination of phobia-inducing objects

To make living with a severe phobia even more distressing, people who have phobias also experience an exaggerated expectation that they may encounter the object of their phobia. This is called expectancy bias, and it also has a correlation with brain activity. Researchers have found that among people who suffer from phobias, expectancy bias is highly associated with under activity of the lateral prefrontal cortex and the visual cortex. Based on the known roles of these areas, study authors explained this finding as a deficiency of cognitive control in relation to the phobia-inducing object, which serves to prime an individual suffering from phobia to anticipate an encounter with the object of distress. A rope may appear to be a snake, even in a setting where there are no snakes. Spilled cocoa may evoke fears of blood and thread may appear to be a spider.

As a physician, how do you respond when dealing with a patient who has a phobia of blood?


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