A part of the brain linked to guilt may explain the vicious circle of negative thinking suffered by people with Obsessive Compulsive Disorder (OCD), a study has found.
The findings could lead to new ways of treating the distressing disorder.
A key characteristic of OCD is believing that negative thoughts will become a reality, leading to a spiralling build-up of anxiety and guilt.
The new study looked at brain wave patterns in people with varying degrees of OCD symptoms.
Scientists found that feelings of anxiety and guilt were associated with increased activity in a brain region called the precuneus.
Previous research has linked the precuneus with the processing of self-attribution, responsibility, causal reasoning, and "moral transgression" guilt.
Psychopaths, who lack a sense of guilt, have been shown to possess a small precuneus.
Study leader Professor Joydeep Bhattacharya, from Goldsmiths, University of London, said: "OCD sufferers experience more guilt and anxiety out of the kind of negative thoughts we might all have from time to time.
"For example, they might imagine a loved one dying in a car crash and believe that somehow it increases the chances that it will actually happen.
"Once they have these thoughts, they feel guilty and subsequently make attempts to suppress and neutralise them, but fail, so entering into a vicious circle."
Precuneus activity was found to be greater in individuals with more extreme OCD symptoms. Activity increased when an individual experienced greater "thought-action fusion" - the belief that a negative event will become reality.
Co-author Dr Rhiannon Jones, from the University of Winchester, said: "These findings could possibly prove to be a significant step towards treating OCD.
"Our next step is to use brain stimulation methods to attempt to modify thought-action fusion. That will allow us to confirm the causal role of these neural findings, and hopefully find a way to reduce these harmful thought-cycles."
The research was published in the journal Neuroimage: Clinical.