It is well known that schizophrenic patients often report that their own actions are controlled by others or some outside forces. These actions can be trivial such as opening a door or writing letters. There are also more complicated types, such as "They inserted a computer in my brain. It makes me turn to the left". It is obvious that patients have a kind of delusion of control.
On the other hand, there is a similar neurological disorder which is known as 'alien hand' or 'anarchic hand' syndrome. It is associated with damage to the supplementary motor area in the cortex. The hand contralateral to the lesion performs goal-directed actions which are not intended by the patient. Sometimes the 'alien' hand interferes with the actions which the 'good' hand is trying to do.
[see Feinberg, T. E. (2001) Altered Egos: How the Brain Creates the Self, Oxford U. P.]
Frith et al. compare these symptoms and point out the important difference between them as follows;
[T]he patient with an anarchic hand recognizes that his hand is performing actions that he has not intended....But he does not conclude that his hand is being controlled by alien forces. In contrast, the patient with delusions of control carries out the actions he intends....and yet, at the same time, he experiences these actions as being made for him by alien forces.
[Frith, C. D. et al. (2000). Explaining the symptoms of schizophrenia: Abnormalities in the awareness of action. Brain Research Reviews 31: 357-363]
The difference is interesting enough. The patient with an alien hand don't have the sense of control of his 'alien' hand, but he still has the normal sense of ownership of it. Instead, the patient with schizophrenic delusion can control his movements but he doesn't have the normal sense of body ownership.
This suggests a lot of things to think about our sense of body ownership and our sense of agency for action.
