Evidence that aetiological risk factors for psychiatric disorders cause distinct patterns of cognitive deficits

Schizophrenia and bipolar disorder are associated with neurocognitive symptoms including deficits in attentional set shifting (changing attentional focus from one perceptual dimension to another) and reversal learning (learning a reversed stimulus/outcome contingency). Maternal infection during gestation and chronically flattened glucocorticoid rhythm are aetiological risk factors for schizophrenia and bipolar disorder. We hypothesised that these factors are causative in the neurocognitive deficits observed in schizophrenia and bipolar disorder. Here we used maternal immune activation (MIA) as a rat model of maternal infection, and sub-chronic low dose corticosterone treatment as a rat model of flattened glucocorticoid rhythm. For comparison we examined the effects of sub-chronic phencyclidine - a widely used rodent model of schizophrenia pathology. The effects of these three treatments on neurocognition were explored using the attentional set shifting task - a multistage test of executive functions. As expected, phencyclidine treatment selectively impaired set shifting ability. In contrast, MIA caused a marked and selective impairment of reversal learning. Corticosterone treatment impaired reversal learning but in addition also impaired rule abstraction and prevented the animals from forming an attentional set. The reversal learning deficits induced by MIA and corticosterone treatment were due to increases in non-perseverative rather than perseverative errors. Our data indicate that the cognitive deficits of schizophrenia and bipolar disorder may be explained by aetiological factors including maternal infection and glucocorticoid abnormalities and moreover suggest that the particular spectrum of cognitive deficits in individual patients may depend on the specific underlying aetiology of the disorder.