Impaired top-down processes in schizophrenia: a DCM study of ERPs.

Perception is not simply based on a hierarchical organization of the brain; it arises from an interplay between inputs from the environment and internal predictions of these inputs. It is an active process which involves an interaction between bottom-up information coming from the senses and feedback connections coming from higher-order cortical areas. In our experiment, we use the hollow-mask illusion to investigate the strength of top-down processes in schizophrenic patients and healthy controls. By using dynamic causal modelling (DCM) on functional magnetic resonance tomography (fMRI) data, we have presented evidence to suggest that patients with schizophrenia are less constrained by top-down processes during perception (Dima, D., Roiser, J.P., Dietrich, D.E., Bonnemann, C., Lanfermann, H., Emrich, H.M., Dillo, W., 2009. Understanding why patients with schizophrenia do not perceive the hollow-mask illusion using dynamic causal modeling. Neuroimage 46, 1180-1186). In this study, we re-address this issue by using DCM on event-related potentials (ERPs) data. Our aim was to validate our previous findings by conducting the same connectivity analysis--DCM--on data obtained from a different neuroimaging method. Our results confirm our initial hypothesis that top-down influences are constrained in schizophrenia, especially in perceptual tasks that require top-down control, like the hollow-mask illusion.