Which of the following is a symptom indicating psychosis?

The presence of symptoms indicating psychosis often involves delusions or hallucinations that disrupt an individual’s perception of reality. In this case, the feeling that "people are putting thoughts into his brain" is a classic example of a delusion, specifically a delusion of control, where an individual believes that external forces are manipulating their thoughts or actions. This reflects a significant distortion in thinking and perception, which is characteristic of psychotic disorders.

The other symptoms described in the options involve different experiences. For instance, an increased heart rate pertains more to anxiety or panic reactions rather than psychosis. Feeling unable to stop eating could be related to binge eating disorders or other behavioral issues but doesn't inherently signify a break from reality. Finally, the inability to pay attention could suggest ADHD or other cognitive issues but does not directly indicate psychosis either. Thus, the sensation of others controlling thoughts is the hallmark symptom signifying psychosis, distinguishing it from the other options provided.