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Prepulse Inhibition

When chatting at a party, we are able to concentrate on our own conversation, and block out what is happening around us. This ability is impaired in people with schizophrenia. By measuring the blink reflex we can record how people react to stimuli.

Our reaction to startling stimuli - termed the startle response - is well documented and has been observed in different species for over 50 years. The stimulus is usually a loud noise, but can be something tactile, like a controlled gush of air on the body. It has been noted that our startle response to a stimulus is decreased if it is preceded by just milliseconds by a weak signal called a prepulse (shown below). Prepulse inhibition (PPI) - the diminished startle response when the startling stimulus is preceded by a weak prepulse - is believed to be an indication of our ability to filter and process information. An important model for studying brain function, PPI has been measured by researchers in SCP to investigate the effects of smoking and drugs on the brain. Still not much is known about the pharmacology of PPI but studies on humans and animals show that nicotine enhances PPI. Researchers in SCP are now looking at brain function during fMRI to find out more about the neural substrates of PPI.

What is PPI?

In humans, the response to stimulus, for example a loud noise, can be measured from the blink reflex, by measuring the movement of a muscle by the eye. When a single stimulus is given, the response is larger than when that stimulus is preceded by a weaker prepulse. This phenomenon is PPI.

PPI in schizophrenia

PPI is an important model for examining brain function in schizophrenia; PPI neither increases nor decreases with practice it is exhibited by most other mammals. In animals, PPI can be altered by pharmacological, developmental or genetic means and this has provided a meaningful model for studying schizophrenia and for predicting the effectiveness of potential therapies. PPI is believed to reflect our ability to screen out irrelevant information. In support of this belief, people with difficulties in filtering sensory information, such as those with schizophrenia, often show decreased prepulse inhibition. Animal studies have shown certain areas in the brain - the limbic system and basal ganglia - are implicated in PPI. PPI deficits found in schizophrenia correlate with deficits in neuropsychological tests.