The Neurobiology of Body Dysmorphic Disorder

By Tsz Man Lai, Wei Li, & Jamie Feusner, MD

Body dysmorphic disorder (BDD) is a psychiatric illness in which people misperceive defects in their appearance, disrupting their ability to function in their daily lives with disturbing preoccupations and emotional distress. Although the clinical symptoms of BDD are fairly well established, little is known about the causes or how the symptoms develop and progress over time.

Researchers in recent years have begun to build knowledge about how BDD sufferers’ brains function. This article will summarize published research studies to date on the neurobiology of BDD, particularly findings related to neurocognitive functioning, neurochemistry, genetics, visual system, and brain structure.

Neurocognitive Function

Memory:

Individuals with BDD show abnormalities in several areas of cognitive functioning including deficiencies in memory1. In one study of cognitive functioning, subjects were asked to copy and recall a complicated figure drawing. The BDD group recalled more specific parts of the drawing instead of the overall structure. This suggests that those with BDD may have visual memory deficiencies, which may be influenced by poor organizational strategies and marked by an imbalance in local (detail) and global information processing.

Decision-making, planning, inhibition, and organization:

BDD individuals also do poorly in tasks related to decision-making, specifically those involving planning, inhibition, or organization2, 3.  One study found that BDD subjects made more errors on a search task, demonstrating deficits in working memory, compared to healthy controls. They also were slower on a task measuring planning ability.

Emotional processing:

Studies on emotional processing revealed that individuals with BDD have deficiencies in recognizing facial emotions.  One study found that individuals with BDD were more likely than healthy controls to misidentify neutral faces as angry4. This suggests irregularities in brain regions that process facial emotion.

Another study found that, compared with healthy participants, BDD individuals perceive ambiguous situations as more threatening, whether the situations were related to the body, or were social or general situations5. In another study, researchers found that BDD participants have more delayed responses to words that are considered salient to people with BDD, such as beauty or attractive, compared with neutral words6.

Neurochemistry

Serotonin system:

Neurochemical studies in BDD thus far have primarily focused on how the brain chemical serotonin is related to nervous system function. The few studies of this suggest that serotonin might play a role in BDD. One study found decreased serotonin binding densities in BDD individuals when compared with healthy controls7. Several treatment studies using medications called serotonin reuptake inhibitors showed that they decrease BDD symptoms overall.  These medications reduce the frequency and severity of worries about appearance.  They also help relieve BDD-related emotional distress, reduced suicidal thinking, and improved patients’ insights into their illness8. However, this does not prove that BDD patients have low serotonin levels or that abnormal serotonin levels cause BDD.  More research is needed to uncover what, if any, neurochemical abnormalities are associated with BDD.

Genetics and Heritability

There have only been a very few genetic studies in BDD. However, there is evidence that BDD is heritable.  Eight percent of individuals with BDD have a family member also diagnosed with BDD – a rate 4 to 8 times higher than in the general population9. A study of female twins found that genes accounted for about 44% of the propensity for dysmorphic worries10.  A small, preliminary study found an association between two different genes and BDD11.

Visual Processing

Several different types of studies have demonstrated that individuals with BDD have abnormalities when processing visual information.

Brain imaging studies:

A neuroimaging technique called functional magnetic resonance imaging (fMRI) allows researchers to compare brain activation patterns between BDD and healthy control subjects, in order to pinpoint the areas and systems in the brain that may be abnormal.  The first functional neuroimaging study in BDD examined visual processing of others’ faces12.  In this experiment, the pictures of faces were altered to remove high or low spatial frequencies, creating images that contained only holistic and configural, or detailed information, respectively. The results revealed that the BDD group had greater activity than healthy controls in regions within the face processing network of the brain on the left for low and normal spatial frequency images.  Healthy controls, as other previous studies also demonstrated, showed a right-hemisphere dominant pattern during the task. The findings suggest the brains of BDD individuals engage in more detailed processing systems (generally left-sided) relative to those involved in holistic and configural processing (generally right-sided), even for images that contain little detail.

The same group performed a similar fMRI study using the subjects’ own faces as stimuli. They found decreased activation in primary visual areas in the BDD group relative to controls when viewing low spatial frequency images, as well as increased activity in frontal and subcortical structures (“frontostriatal” regions) when viewing normal images13.  In addition, symptom severity (primarily relating to severity of obsessive thoughts and compulsive behaviors) was correlated with activity in secondary visual systems and frontostriatal systems in BDD subjects.  The abnormal frontostriatal activity in this imaging study is similar to what other studies have observed in obsessive-compulsive disorder, a related disorder; this may underlie BDD individuals’ obsessive thoughts and compulsive behaviors.

In a separate study, BDD patients were asked to do the same matching task but with images of houses14.  This study found that they had decreased activity in secondary visual processing regions compared with healthy controls in response to low spatial frequency images.  This offers more evidence of abnormal holistic processing.  The fact that this occurred for non-appearance-related stimuli suggests that those with BDD may have general deficiencies in visual processing.  Abnormal holistic and configural visual processing could contribute to distortions in perceptions.  Their brains may not provide adequate visual “templates” for them to integrate and contextualize details such as minor flaws or imperfections.

Studies of face processing:

Differential ability to detect flaws in facial features or asymmetry is another aspect of visual processing that researchers have studied in individuals with BDD.  In one study, BDD participants perceived distortions in digital images of their own faces that were not actually present15. In another study, BDD participants were more accurate than healthy controls in detecting changes in aesthetic features of others’ faces16.  Two studies17,18, but not a third19 found that those with BDD were faster than healthy controls at identifying others’ faces that were upside down, suggesting they have a superior ability to process details. These studies suggest that BDD individuals have heightened sensitivity to detecting details, which may lead them to notice defects that are very minor or unnoticeable to others.

Brain Structure

Studies of brain volumes:

Several BDD studies have examined brain volumes.  One small study found that females with BDD have more total white matter and abnormal symmetry in a subcortical region called the caudate nucleus, compared with healthy controls20. A study in males with BDD also found greater total white matter, as well as smaller gray matter volumes in frontal regions called the anterior cingulate and the orbitofrontal cortex, on the left and the right21.  A third study in males and females also found that the right orbitofrontal cortex and left anterior cingulate cortex were smaller in BDD participants than healthy controls22. Moreover, the longer they had BDD, the smaller were their right orbitofrontal cortices.

These studies provide evidence of abnormalities in frontostriatal systems in BDD individuals.  However, a third study did not find brain differences between BDD and control groups.  It did find a correlation between symptom severity and volumes in a region of the frontal cortex called the inferior frontal gyrus, and the right amygdala, a subcortical structure crucial to processing of emotions23.

These studies are not entirely consistent with each other.  This may be due to the fact that each one studied relatively few individuals, one included just females20, one included just males21, and one included subjects on medications, which may have affected brain volumes22.

Studies of brain white matter:

Measurements of the structural integrity of white matter, brain tissue that transmits signals between different parts of cortex, can be determined using a neuroimaging technique called diffusion tensor imaging (DTI). One DTI study found that the clinical measure of poor insight in BDD correlated negatively with a measure of fiber integrity in white matter tracts connecting visual with emotion/memory processing systems24. Another brain study found lower fiber integrity in many major white matter tracts in the brains of individuals with BDD compared to healthy control participants, suggesting a more disorganized white matter structure in BDD25.

Brain connectivity studies:

A brain network analysis of white matter connectivity in individuals with BDD discovered greater local clustering of networks across the whole brain26.  There was also a strong correlation between low efficiency of connections and severity of BDD symptoms.  In addition, there were specific abnormal connections between regions involved in lower level and higher level visual and emotional processing.  This may be associated with a disturbance in how visual information is processed emotionally in those with BDD.

Summary of studies of brain structure:

There is some evidence (albeit inconsistent) of abnormal gray matter volumes and reduced white matter integrity.  In addition, there is evidence of abnormal white matter brain connectivity (“the wiring”) in people with BDD. Inefficient connections between these brain regions may underlie impairments in visual, emotional, and possibly other types of information processing.

Conclusions

BDD is a complex psychiatric disorder that includes symptoms that span many domains, and thus the neurobiology is likely equally as complex.  However, several patterns are emerging from evidence from research studies of the following:

  1. Impairments in neurocognitive functioning, especially in planning, organization, and memory
  2. Visual and emotional processing deficiencies
  3. Impairments in frontostriatal circuits that mediate higher-level regulation and control
  4. Abnormal white matter connectivity and network patterns in the brains of those with BDD

Interactions between these aberrantly functioning brain systems, as well as possible abnormalities in neurotransmitter/neurochemical systems may contribute to many of the symptoms in BDD.

Promising new research has started to identify abnormal areas and connections in the brain, in hopes of developing biomarkers or brain correlates that can help identify those at risk for developing BDD.  Because of the complexity of the disorder, much future research is necessary to understand what causes BDD and contributes to the development of BDD symptoms (including neurobiological as well as interpersonal, social, cognitive, and behavioral factors) and how those findings can lead to better treatment methods.

References

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