Brain injury can change your personality - this is common in prisoners. E.g Phineas Gage survived a metal rod through the brain but changed his personality. Some brain diseases have been linked with criminal behaviour. E.g. dementia. Some studies show abnormal PET & EEG readings in psychopathic criminals. Several research studies suggest that damage to the pre-frontal cortex of the brain may cause the individual to act immaturely or lose self-control. Crimes caused by brain injury or disease are rare and abnormal EEG is not necessarily found in all psychopaths.
