According to the authors of Ghosts from the Nursery, excessive shame results in hypoarousal of the brain, the opposite of excitement and playfulness. This can impact the development of empathy. If the synapses in the brain are never built in childhood due to neglect, or if they are destroyed by neurochemicals resulting from chronic stress, the individual may be left with the ability to connect, trust, or experience empathy. Extreme instances may result in the development of sociopathy. This was enlarged upon by the authors of Liars, Lovers, and Heroes, who estimated that sociopaths form about 20% of the prison population while only represented in a small fraction of the general population. Many of these individuals appear insensitive to the threat of punishment. Also, many were abused as children and never learned to empathize with the pain and suffering of others. Brain scans showed an 11% reduction in gray matter volume in the prefrontal area of the brain (compared with a control group).