Leah Suissa-Rochelau

Simulating Thought Insertion Using Deception

Background: Delusions of being controlled by an outside source are a prominent concern for those suffering with psychotic disorders. One example of these sorts of delusions is called thought insertion, the belief that a thought is inserted into one’s mind from another source.

Methods: In order to study these kinds of delusions more closely, we used suggestion to mimic the appearance of these symptoms in healthy participants. More specifically, we made participants believe that we were inserting thoughts into their heads by using a new kind of neuroimaging technology. Through our simulated thought insertion paradigm, we were able to manipulate healthy participants’ feelings of volition in making decisions. Participants (N=27) completed two tasks inside a mock brain scanner: the Mind- Reading Task and the Mind-Influencing Task. In the Mind-Reading Task, participants were led to believe that the machine, by scanning their brain activity, could guess a number they previously chose. In the Mind-Influencing Task, the scanner ostensibly influenced the participant’s choice of number. This paradigm used mentalism magic in order to match the machine’s (bogus) output to the participant’s choice.

Discussion: Results showed that participants made slower and less voluntary decisions in the Mind-Influencing Task, indicating that their sense of acting according to their free will was reduced. We replicated this pattern of results in a subsequent study (N=23). Through interviews, we found that participants’ phenomenological experience varied. Many expressed a more reasoned thought process in the Mind-Reading Task than in the Mind-Influencing Task. People in the Mind-Influencing Task reported that the decision did not feel like their own, that they were not able to change it, or that the thought came from an uncontrollable source. These unusual experiences were sometimes accompanied with odd bodily sensations like pulsations or heat around the head. This novel research paradigm may be useful to model symptoms of psychotic disorders. Modeling these symptoms may in turn aid understanding and guide future research studying the mechanisms sustaining these delusions in individuals suffering from psychosis.