PATHOGENESIS OF SCHIZOPHRENIC DELUSIONS AND HALLUCINATIONS - A NEURALMODEL

We implement and study a computational model of Stevens' theory of the pathogenesis of schizophrenia. This theory hypothesizes that the onse t of schizophrenia is associated with reactive synaptic regeneration i n brain regions that receive degenerating temporal lobe projections. C oncentrating on one such area, the frontal cortex, we model a frontal module as an associative memory neural network whose input synapses re present incoming temporal projections. Modeling Stevens' hypothesized pathological synaptic changes in this framework results in adverse sid e effects similar to hallucinations and delusions seen in schizophreni a: spontaneous, stimulus-independent retrieval of stored memories focu sed on just a few of the stored patterns. These could account for the delusions and hallucinations that occur in schizophrenia without any a pparent external trigger and for their tendency to concentrate on a fe w central cognitive and perceptual themes. The model explains why the positive symptoms of schizophrenia tend to wane as the disease progres ses, why delayed therapeutic intervention leads to a much slower respo nse, and why delusions and hallucinations may persist for a long time when they do occur.