Functional movement disorders (FMD) are part of the spectrum of functional neurological disorders (FND), which are common and disabling. Nowadays, it is widely accepted that key aspects of the underlying pathophysiology include the tendency to form abnormal beliefs about symptoms, disturbance of attentional control and disruption of mechanisms regulating sense of agency.1

‘Jumping to conclusions’ bias (JTC) is a probabilistic reasoning style characterised by making firm decisions based on insufficient evidence. This cognitive bias has been studied to assess erroneous belief formation in delusions by using the classical paradigm of ‘the bead task’.2 In 2012, we explored the JTC bias for the first time in patients with FMD. We found that they required less evidence to reach a decision than healthy controls.3

Here, we aimed to confirm the presence of the JTC bias in a new and larger cohort of patients with FMD and compare the results with a control group of patients diagnosed with major depressive disorder (MDD). Additionally, we evaluated whether changing uncertainty by manipulating the initial information in the bead task might impact participants’ behaviour.

We recruited 23 consecutive patients with FMD from the Neurology and 26 patients with MDD from the Psychiatry Department of the Ramón y Cajal Hospital, Madrid, Spain. Participants ≥18 years with a clinically established/documented FMD were included. A Mini-mental State Examination (MMSE) score ≤26 was an exclusion criterion.

The reasoning task was like previous designs.2 3 In the ‘draws to decision’ methodology, participants were presented with 2 jars each containing 100 beads. In condition 1, jar A contained 85 red and 15 blue beads and jar B contained 85 blue and 15 red beads. …