Clinical relevance of animal models of schizophrenia

Animal models and endophenotypes of mental disorders are regarded as preclinical heuristic approaches aiming at understanding the etiopathogenesis of these diseases, and at developing drug treatment strategies. A frequently used translational model of sensorimotor gating and its deficits in some neuropsychiatric disorders is prepulse inhibition (PPI) of startle. PPI is reduced in schizophrenia patients, but the exact relationship between symptoms and reduced PPI is still unclear. Recent findings suggest that the levels of PPI in humans and animals may be predictive of certain cognitive functions. Hence, this simple measure of reflex suppression may be of use for clinical research. PPI is the reduction of the acoustic startle response that occurs when a weak prestimulus is presented shortly prior to a startling noise pulse. It is considered a measure of sensorimotor gating and is regulated by a cortico-limbic striato-pallidal circuit. However, PPI does not only occur in the domain of startle. PPI of alpha, gamma, and theta oscillations at frontal and central locations has been found, suggesting a relationship between PPI and cognitive processes. In fact, levels of PPI in healthy subjects and in animals predict their performance in cognitive tasks mainly mediated by the frontal cortex. Taken together, PPI might reflect a more general filtering performance leading to gating of intrusive sensory, motor, and cognitive input, thereby improving cognitive function. Hence, PPI might be used in clinical settings to predict the impact of drugs or psychotherapy on cognitive performance in neuropsychiatric patients.