Prepulse inhibition

Pre-pulse inhibition (PPI) is a research (animal) model of a part of Schizophrenia, a complex disease. Creating animal models of the whole disease is difficult; therefore, it has been the objective of researchers to model individual parts of the illness.

PPI&mdash;the inhibition of the startle reflex, caused by a preceding weak stimulus&mdash;is comparable to oversensitivity to stimuli seen in schizophrenic patients, and is thought to be a measure of deficit in sensorimotor gating (Braff, Gayer, et al 1990).

The animal is placed in an automated box with a sound source and motion sensor, and the response to the ‘startle’ is measured. The animal is acclimatised to the background noise, and a prepulse of around 7-12db above background levels can be initiated, followed by a more intense stimulus around 30 to 500ms later. The PPI is calculated by measuring the reduction of the startle response in comparison to controls that don’t carry a prepulse. There are four distinct categories of PPI, related to the manipulation used to disrupt it: Glu agonists, 5-HT agonists, DA agonists, and developmental manipulation. These correlate with current theories of schizophrenia especially as current antipsychotics antagonise the effects on PPI (for review see Geyer & Krebs – Homson 2001). In addition to animal models, PPI has also been explored in humans, supporting the validity of these procedures in studying schizophrenia (for review, see Braff et al. 2002).