The scientists from the Department of Forensic Medicine, of the Medical University of Vienna, surprisingly found that addictive cravings can be detectable even after death.
This is due to a protein known as FosB, which is present in the reward centre of the brain. The protein gets altered in chronically ill people who are suffering from an addictive disorder such as heroin addiction. The protein then is genetically modified, split off and shortened. When under the stimulus of a drug, this type of modification results in the protein being more stable leading it to remain longer in this part of the brain than in its original form. This can be as long as several weeks even after withdrawal of the drug. Thus, craving for this stimulus persists which leads to this addictive craving getting stored in a sort of “memory” function and can still be detected after death.

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https://www.sciencedaily.com/releases/2016/12/161221090114.htm