Researchers may have discovered a biological basis for intermittent explosive disorder (IED), a condition in which sufferers regularly fly into fits of rage after mistaking the social signals given off by others, leading them to believe that people are trying to antagonize them. According to a new study appearing in the journal Neuropsychopharmacology, those who suffer from the condition have reduced connectivity between brain regions that process emotion, language and sensory input, as the volume of white matter linking these regions is less dense than it should be.
White matter is a type of brain tissue that carries messages between different areas of the brain, allowing them to communicate with one another. One particular channel of white matter is known as the superior longitudinal fasciculus (SLF), which study co-author Royce Lee described in a statement as “an information superhighway connecting the frontal cortex to the parietal lobes.”
Using a technique called diffusion tensor imaging, the researchers discovered that those suffering from IED have a reduced density of white matter in the SLF compared with those who do not have the condition. Given the frontal cortex is heavily involved in decision-making and emotion, and the parietal lobes process language and sensory stimuli, a weakening of this connection would tend to suggest that explosive rage may be a product of an inability to correctly interpret one’s interactions with other people.
White matter regions with reduced density in IED sufferers. Lee et al., Neuropsychopharmacology
In their paper, the authors describe this finding as “unexpected but intriguing,” particularly given the fact that white matter abnormalities in the SLF have previously been associated with a range of other conditions such as anorexia and borderline personality disorder.
The results of this study also add further weight to the idea that many psychological disorders might be produced not so much by deformities in the actual structure of the brain, but by defects in connectivity between regions. According to Lee, this connectivity “might be where we’re going to see a lot of the problems in psychiatric disorders, so white matter is a natural place to start since that’s the brain’s natural wiring from one region to another.”
Indeed, previous studies have already indicated that criminal psychopathy is largely caused by reduced white matter in the uncinate fasciculus, which connects the amygdala to the prefrontal cortex.
Summing up this research, study co-author Emil Coccaro explained that “this is another example of tangible deficits in the brains of those with IED that indicate that impulsive aggressive behavior is not simply ‘bad behavior’ but behavior with a real biological basis that can be studied and treated.” Furthermore, the fact that white matter density in the SLF is partly heritable suggests that IED could also be genetic.
