IED brain connectivity
People with IED may have abnormal white matter density in their brain.Istock

People who suffer from anger disorders may have weakened connections between regions of the brain associated with sensory input, social interaction and language processing, scientists have said. The brain's white matter in these areas may take on an abnormal aspect in individuals affected by intermittent explosive disorder (IED) – a disorder characterised by episodes of sudden rage.

White matter connectivity in the brain is known to play a crucial role in the regulation of social and emotional behaviours, and this research – published in the journal Neuropsychopharmacology – investigates how it plays a role in impulsive aggression.

Brain scans and white matter density

The team, from the University of Chicago, recruited 132 male and female adults between the ages of 18 and 55 years. 42 subjects had IED, 40 were normal controls, and 50 were clinical psychiatric controls with psychiatric disorders without IED.

All went through diffusion tensor imaging, a form of magnetic resonance imaging (MRI) that measures the volume and density of white matter connective tissue in the brain.

The scientists discovered that white matter in a region of the brain called the superior longitudinal fasciculus (SLF) has less integrity and density in people with IED than in healthy individuals and those with other psychiatric disorders.

The SLF connects the brain's frontal lobe – responsible for decision-making, emotion and understanding consequences of actions – with the parietal lobe, which processes language and sensory input. This abnormal white matter density results in weakened connections between those two brain regions.

"It's not so much how the brain is structured, but the way these regions are connected to each other," lead-author Royce Lee says. "That 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."

Reading social situations

These findings may explain why people with IED tend to misunderstand the intentions of other people in social situations, viewing them as hostile, and thus becoming angry.

Decreased connectivity between regions of the brain that process social situations may indeed lead to impaired judgement that escalates to an explosive outburst of anger. The lower-than-normal white matter density may mean that people do not take in all the data and notice only those things that reinforce their belief that the other person is challenging them.

"This is an example of tangible deficits in the brains of those with IED that indicate that impulsive aggressive behaviour is not simply 'bad behaviour' but behaviour with a real biological basis that can be studied and treated," senior author Emil Coccaro concludes.