Multisensory causal inference in cortical hierarchies and its alterations in schizophrenia

• Applicant: Professor Tim Rohe, Ph.D.
• Subject Area: Clinical Psychiatry, Psychotherapy, Child and Adolescent Psychiatry ; Biological Psychiatry ; Human Cognitive and Systems Neuroscience
• Term: from 2017 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 390070110

Humans integrate signals from multiple senses to obtain a coherent and more reliable multisensory representation of their environment. The brain integrates the signals, weighted by their relative sensory reliability, only if a small signal disparity suggests a common source. Otherwise the signals are segregated. The brain infers the signals´ causal structure from the signals´ spatiotemporal and structural disparity. Our previous and current work suggests that dorsolateral prefrontal cortex (dlPFC) first decides on the signals´ causal structure basing on their disparity before anterior intraparietal sulcus (aIPS) integrates the signals weighted by their reliability in case of a common source. However, this model of multisensory causal inferences in cortical hierarchies is not yet empirically tested. Further, multisensory causal inference might be affected in schizophrenia leading to symptoms such as hallucinations. Hence, in three studies we aim at investigating three open questions: In study 1, we will investigate where, when and how the cortical hierarchies make a causal decision and integrate or segregate audiovisual numeric signals. In a simultaneous EEG-fMRI study, 15 healthy participants will complete an audiovisual numerosity paradigm presenting a sequence of flashes and beeps. Basing on the signals´ numeric disparity, we expect that dlPFC first decides on the signals´ causal structure. Depending on the causal decision, aIPS subsequently integrates the signals weighted by their reliability or segregates the task-irrelevant signal. In study 2, we will investigate whether dlPFC and aIPS are causally involved in the causal decision and integration process, respectively. 15 healthy participants will complete the audiovisual numerosity paradigm while we apply online TMS pulses at different time points during stimulus processing. Because the causal decision should precede the integration process, we expect that earlier TMS pulses to dlPFC will disturb the causal decisions. Later TMS pulses to aIPS will disturb the integration process. In study 3, we will investigate whether, when and in which regions schizophrenia alters multisensory causal inference. During simultaneous EEG-fNIRS measurements, 25 schizophrenia patients and 25 matched healthy participants will complete a variant of the audiovisual numerosity paradigm presenting a number of faces and voices. We assume that the cortical hierarchies of schizophrenia patients more generally integrate multisensory signals irrespective of the signals´ causal structure, thus potentially leading to hallucinatory percepts. Overall, the studies will provide a deeper understanding of how cortical hierarchies implement multisensory causal inference and potentially disclose new neuropathological mechanisms of schizophrenia symptoms.

• DFG Programme: Research Grants