Neural network simulations, cortical connectivity, and schizophrenic psychosis.

Recent studies have suggested that reduced corticocortical connectivity is associated with schizophrenia. My colleagues and I have used neural network simulations to explore parallel, distributed processing systems with reduced connectivity. These systems often behaved in a "schizophrenic-like" manner. Excessively pruned attractor networks became functionally fragmented, suggesting "loose associations," and produced recurrent, intrusive representations suggestive of delusions. Pruning backpropagation simulations of speech perception networks produced spontaneous output, which provided a model of auditory hallucination or "voices." This model also suggested how dopamine-blocking drugs may reduce positive symptoms, and why negative symptoms arise in the wake of positive symptoms.