Abstract
Background
The 22q11.2 deletion syndrome (22q11DS) represents one of the highest genetic risk factors for developing schizophrenia. About 30% of individuals develop symptoms like hallucinations, thought disorders, passivity symptoms or loss of agency. These symptoms could be driven by abnormal sensorimotor predictions associated with the misattribution of self-related events to external sources (Frith, 2005). We developed a robotic device altering sensorimotor processing in healthy subjects and inducing mild to moderate hallucinations (presence hallucinations - PH) and passivity experiences (Blanke et al., 2014). Using this new device and procedure, we tested the sensitivity of individuals with 22q11DS to sensorimotor conflicts provided by the robot and their proneness in experiencing robot-induced PH and related passivity experiences as compared to healthy controls.
Methods
Thirty-eight individuals with 22q11DS and 21 controls moved, with the hand, a robotic device placed in front of them. A second robot placed behind them reproduced their movements, thus delivering tactile feedback on their back either synchronously (0ms between the movement and the touch, sync) or asynchronously (delay of 500ms, async) (Blanke et al., 2014). Participants rated the strength of robot-induced PH, passivity experiences that they felt during robot manipulation, and control items. Occurrence and severity of clinical symptoms were assessed.
Results
Subjective ratings following robot manipulation were analysed, and age was used as covariate. In the asynch condition, participants reported significantly stronger loss of agency over their hand movements and there was a trend towards a significant interaction between group and conditions for loss of agency with control subjects experiencing more loss of agency in the asynchronous condition than 22q11DS participants. A trend for significance was also observed whereby all subjects reported stronger PH in the asynchronous condition than in the synchronous condition. No significant group effect was observed for the subjective ratings associated with the robot manipulation. For the 22q11DS group, severity scores for items of unusual thought content/delusional ideas of the Structured Interview for Prodromal Syndromes positively and significantly correlated with ratings of robot-induced PH and loss of agency in the async condition. Passivity experiences during the async condition (i.e., the subjective impression that someone else was touching their back) significantly correlated with severity scores for perceptual abnormalities/hallucinations items.
Discussion
Experimental induction of sensorimotor conflicts caused mild altered mental states in individuals with 22q11DS as reported for controls. Both 22q11DS and control groups showed more sensitivity to the asynchronous condition during which they perceived loss of agency and passivity over their own actions, suggesting that the robotic stimulations disrupted self-other demarcation. In 22q11DS individuals, induced-PH, passivity experiences and loss of agency felt during the robot manipulation was associated to unusual thought content and abnormal perception. Taken together, our results suggest that 22q11DS is an interesting model to study the development of prodromal signs of psychosis at a very early stage before the onset of schizophrenia.
Childhood cognitive development in 22q11.2 deletion syndrome: Case–control study