Psychosis and Subjective Reality

 

A major hypothesis trying to explain psychosis also focuses on the same fundamental mechanism which seems to be involved in the placebo effect, i.e. on expectations and error processing.  It suggests that weak expectations and/or overly salient input signals allow for an imbalance in the system in favor of the input signal. Possibly an aberrant or overly strong dopamine signal is involved in this mechanism by assigning a different salience to this input. This overly strong signal propagates in the brain to the highest hierarchies. Ultimately, this faulty signals may update the expectation system in an erroneous way and thereby construct delusions and hallucinations. In order to test these models we have started to manipulate expectations in a similar way as has been done in placebo research previously. We have so far been able to show that such expectation manipulation of a visual illusion has a larger impact in psychosis prone individuals than in other subjects, and that there is an interaction between prefrontal areas and higher order visual areas that relates to this effect (Schmack et al Journal of Neuroscience 2013). Another study using a moving rubber hand illusion indicates that psychosis prone subjects assign stronger agency based on external input while controls use their expectations (i.e. called efference copy in this case) to assign stronger agency (Kalckert et al 2013 - under review). We believe that this line of studies will increase the understanding of the mechanisms involved in psychosis.