Reduced corticocortical connectivity can induce speech perception pathology and hallucinated 'voices'.

Reciprocal interactions between multiple cortical areas are required for higher-order cognitive processes in animals and humans. A growing body of evidence suggests that reduced cortical connectivity is associated with schizophrenia. We have used neural network computer simulations to characterize symptoms and cognitive pathology that could arise from connectivity reductions. When this pathology was reproduced in simulations of speech perception networks, spontaneous percepts analogous to hallucinated speech were induced due to the emergence of 'locked-in' or 'parasitic' states. We propose that these simulations provide a model for hallucinated 'voices' reported by actual schizophrenic patients. The 'hallucinogenic' model of speech perception also demonstrated subtle speech perception impairments. We have demonstrated similar impairments when assessing schizophrenic patients reporting 'voices', but not when assessing similarly diagnosed patients not reporting this symptom. The model also demonstrates how a 'hypodopaminergic' state can reverse cognitive pathology arising from connectivity disturbances.