The first evidence of white matter abnormalities in rapists have been reported in a study published this July in BMC Neuroscience. Diffusion tensor imaging findings highlighted important differences in areas relating to poor fear conditioning, a tendency for sexual over-arousal, heightened sensitivity to reward and obsessive thinking on sexual themes.

As the rate of sex crimes and number of sexual offenders continue to grow, much effort has been devoted to understanding the nature of these crimes, as well as the characteristics of the offenders. Some have proposed that heterosexual rapists may be over-responsive to sexual stimuli. Others have hypothesized an association between the construct of moral judgment and sexual offenses.

Recent research has documented structural brain abnormalities in various criminal offenders related to sexual arousal and behavior and moral decision-making.

The study, led by Chiao‑Yun Chen of the National Chung Cheng University, involved 15 male sex offenders and 15 control participants, and looked for abnormal cortical and subcortical white matter integrity (Fractional anisotropy) using diffusion tensor imaging. The results revealed a number of key findings.

Firstly, sex offenders had reduced integrity in the posterior cingulum. The posterior cingulum connects a number of key regions linked to conditioning, and thus this may suggest impairments in fear conditioning, known to predispose individuals to criminal behavior.

Secondly, they found increased integrity in brain areas involved in the reward system (caudate, globus pallidus, and thalamus). Previous research has suggested this could contribute to over-activation of brain areas related to sexual arousal.

Thirdly, decreased integrity was found in white matter near the angular gyrus, the posterior cingulate, and the medial frontal pole. Previous studies using functional imaging have reported these regions to be involved in moral decision-making, as well as to be dysfunctional in violent and psychopathic criminals.

Finally, the results revealed increased integrity in several regions of the internal capsule, when compared with the control group. Previous research has linked obsessive–compulsive disorder (OCD) to this region, and the researchers suggested that this could contribute to obsessive thinking on sexual themes.

The study was the first to report white matter abnormalities in rapists. The findings highlight important differences in areas relating to poor fear conditioning, a tendency for sexual over-arousal, heightened sensitivity to reward and obsessive thinking on sexual themes. These areas may potentially contribute to an increased risk for committing rape.