The family of sensorimotor gating disorders: comorbidities or diagnostic overlaps?

Prepulse inhibition (PPI) of startle is an operational measure of the pre-attentive filtering process known as sensorimotor gating. Originally identified in patients with schizophrenia, PPI deficits have been observed in multiple but not all psychiatric disorders. Thus, as with most signs and symptoms of psychiatric disorders, deficits in PPI cut across diagnostic categories. It remains unclear whether the diversity of disorders exhibiting deficient PPI bespeaks diagnostic overlaps or comorbidities. Given the recent focus on treatments for cognitive deficits of schizophrenia independently of treating psychosis, the relationship of PPI deficits to cognitive deficits becomes of interest. Although PPI cannot be considered to be a cognitive process per se, abnormalities in pre-attentive information processing may be predictive of or lead to complex cognitive deficits. Animal models of PPI deficits produced by dopamine agonists reliably predict existing antipsychotics. Nevertheless, since neither PPI nor cognitive deficits in schizophrenia are ameliorated by standard antipsychotics, current research is exploring the predictive value of non-dopaminergic PPI models in identifying treatments for gating disturbances independently of their relevance to specific disorders. Both PPI and cognitive deficits in schizophrenia patients are not reversed by first generation antipsychotics but may be attenuated by clozapine. Similarly, effects of glutamate antagonists on symptoms in patients and PPI in animals appear to be reduced by clozapine. Hence, treatment-induced reversals of deficits in PPI produced by glutamate antagonists may provide animal, and human, models to aid in the discovery of treatments of cognitive deficits in patients already treated with existing antipsychotics.