Posterior Parietal Cortex Modulates Perceptual Decisions Depending On Psychotic Phenotype

Abstract

BACKGROUND. Reduced data-gathering and imbalanced sensory precision have been linked to psychotic-like experiences. These patterns arise in decision tasks that typically involve the posterior parietal cortex (PPC). However, a causal link between activity in PPC and the decision patterns associated with the psychotic phenotype has not been established yet. By the use of 1 Hz repetitive transcranial magnetic stimulation (TMS), we tested whether PPC excitability modulate data-gathering and precision encoding differently in high and low psychotic phenotypes. METHODS. We compared performance in both the random dot motion task (RDM; perceptual inference) and the beads task (probabilistic reasoning) in two groups of participants (total, N = 68) undergoing TMS or sham-TMS over the right PPC. Hierarchical drift-diffusion models estimated drift rates (sensory precision proxies) and decision thresholds. We evaluated differences between TMS and sham-TMS groups and tested for interactions of these TMS groups with delusional and hallucinatory phenotypes. RESULTS. In RDM, TMS increased decision thresholds compared to sham-TMS in the low psychotic phenotype group. This decision threshold effect was not present in participants with higher psychotic phenotypes. Drift rates, in contrast, were lowered in participants with higher delusional phenotype. We did not find any significant effect on beads task performance. CONCLUSIONS. Our findings suggest a causal role of PPC in decisions to end data-gathering during perceptual inference. The absence of this effect in the psychotic phenotype yields new hypotheses on the role of PPC excitability in neural mechanisms underlying decision-making patterns in the psychotic phenotype.