A startle response in reaction to a loud acoustic stimulus is measured by placing mice into an animal holder placed on a transducer platform inside an acoustic chamber and recording the magnitude of the animal's 'reaction' to the stimulus. A weak sound preceding the loud acoustic stimulus inhibits the startle reflex; this is called pre-pulse inhibition of startle (PPI). Several psychotomimetic drugs (eg. amphetamine, PCP, ketamine) disrupt PPI and simulate a psychotic-like state in animals which can be antagonized by anti-psychotics. In rodents, acute administration of PCP or MK-801 can disrupt PPI. Antipsychotic agents will increase the PPI response and also reverse the effects of disrupters.