First, dysregulated fear, i.e. excessive and/or poorly controlled fear responses mediated by fronto-limbic circuitry, has been proposed as a key mechanism in OCD [37] (Table 2 gives a full explanation of neurocognitive functions and their associated neurocircuits, as well as examples of experimental tasks and instruments that have been used to measure these functions). Clinically, some patients report that their symptoms are triggered or maintained by feelings of fear. For example, in Case vignette 1 (Table 1), what seemed to trigger or perpetuate the patient’s obsessive belief that she was pregnant was the physiological fear response to the thought that she could be pregnant (I must be pregnant, or I wouldn’t be feeling like this). Thus, in some patients, dysregulated fear responses to intrusive thoughts mediated by fronto-limbic circuitry could be the starting point that turns ordinary thoughts into obsessions. In support, previous studies investigating the content of patients’ descriptions of their OCD symptoms have revealed that physiological changes associated with fear and anxiety, such as a racing heart, play a key role in triggering a variety of obsessions and
