In 2006, Bartholow, Beushman, and Sestir experimented with brain scanners to record P300 activity while people of various violent backgrounds viewed violent images. They predicted that those who had had high exposure to violence in the past would have a lower P300 reaction during the experiment while viewing violent images. What they found was exactly that: Those who had violent pasts had become desensitized to violent images and therefore had less of a reaction. Neuroscience has been very helpful in trying to understand the brain and its reaction to high levels of constant violence. Beliefs, schemas and knowledge structures are developed and shaped depending on the surrounding environment. Through repeated exposure and acceptance, violence can be seen as something extraordinary and therefore more acceptable and expected in everyday life. Hostile expectancy bias, the expectation that others will be hostile, creates a readily hostile attitude that decreases empathy while increasing consistent aggression. Heightened fear of aggression leads to increased cortisol levels. The effects of constant exposure to violence can change the physical body and lead to desensitization towards violence as such