Major features The magnitude of PPI is often significant, reaching as much as 65\% in healthy subjects . Maximum inhibition is typically observed at 120 ms interval. Baseline startle response does not affect overall PPI levels – this finding was first discovered in rat studies and later duplicated in the studies of mice. The opposite reaction, Prepulse Facilitation (PPF)-- the tendency for a subject to have an increased startle response following a lower-intensity prepulse stimulus—is typically noted when the interval between stimuli lasts longer than 500 ms. PPF is thought to reflect, at least partially, sustained attention: the prepulse, if not followed within less than half a second by the pulse, will tend to make the subject more likely to have a startle response rather than less. There is noted sex difference in prepulse inhibition and facilitation  , with men having higher PPI (i.e., when a prepulse is quickly followed by a pulse, all subjects tend to experience a reduced startle response, with men often experiencing lesser startle responses compared to women) and women having higher PPF (i.e., when the prepulse occurs more than half a second before the pulse, all subjects tend to experience heightened startle responses, with women tending to experience greater startle responses than men). Monaural PPI is higher than binaural—the startle response is reduced when the stimulus (noise) is only experienced in one ear rather than both ears. Even the very first prepulse of a test session induces inhibition, which indicates that conditioning and learning are not necessary for this effect to occur. However, the lack of conditionality has been questioned. However a thousandth prepulse also induces inhibition; the phenomenon is highly robust  It is thought that the short intervals used in PPI task do not give enough time for the activation of a volitional response: the reaction to pulses and prepulses separated by short time frames is believed to be involuntary. Prepulses could be attended or ignored, and attention affects the outcome. In one study, normal college students were instructed to attend to one of the kind of prepulses, high- or low-pitched, and ignore the other. Attended prepulse caused significantly greater inhibition at the 120 ms interval compared to the ignored one, and significantly greater facilitation at the 2000 ms interval. This reflects the tendency of subjects to expect to hear a particular frequency of pulsed sound, an effect that is highly pronounced when the prepulse occurs two seconds before the pulse and when there are other pulses being heard which are being consciously "ignored". Increased prepulse duration leads to increase in PPI: the longer the prepulse, the greater the reduction in subsequent startle responses. Steady background noise facilitates the startle response, while pulsed background produces inhibition.
Major features The magnitude of PPI is often significant, reaching as much as 65\% in healthy subjects , with maximum inhibition is typically observed at 120 ms interval. The baseline startle response does not affect overall PPI levels – this finding was first discovered in rat studies and later duplicated in the studies of mice. The opposite reaction, Prepulse Facilitation (PPF)-- the tendency for a subject to have an increased startle response following a lower-intensity prepulse stimulus—is typically noted when the interval between stimuli lasts longer than 500 ms. PPF is thought to reflect, at least partially, sustained attention: the prepulse, if not followed within less than half a second by the pulse, will tend to make the subject more likely to have a startle response rather than less. Another moderating variable in prepulse inhibition and facilitation is sex difference , with men having higher PPI (i.e., when a prepulse is quickly followed by a pulse, all subjects tend to experience a reduced startle response, with men often experiencing lesser startle responses compared to women) and women having higher PPF (i.e., when the prepulse occurs more than half a second before the pulse, all subjects tend to experience heightened startle responses, with women tending to experience greater startle responses than men). For acoustic stimuli, monaural PPI is higher than binaural—the startle response is reduced when the stimulus (noise) is only experienced in one ear rather than both ears. Even the very first prepulse of a test session induces inhibition, which indicates that conditioning and learning are not necessary for this effect to occur. However, the lack of conditionality has been questioned. However a thousandth prepulse also induces inhibition; the phenomenon is highly robust Response and reaction are affected by interval duration and attention. It is thought that the short intervals used in PPI task do not give enough time for the activation of a volitional response: the reaction to pulses and prepulses separated by short time frames is believed to be involuntary. Prepulses could be attended or ignored, and attention affects the outcome. In one study, normal college students were instructed to attend to one of the kind of prepulses, high- or low-pitched, and ignore the other. Attended prepulse caused significantly greater inhibition at the 120 ms interval compared to the ignored one, and significantly greater facilitation at the 2000 ms interval. This reflects the tendency of subjects to expect to hear a particular frequency of pulsed sound, an effect that is highly pronounced when the prepulse occurs two seconds before the pulse and when there are other pulses being heard which are being consciously "ignored". Increased prepulse duration leads to increase in PPI: the longer the prepulse, the greater the reduction in subsequent startle responses. Steady background noise facilitates the startle response, while pulsed background produces inhibition.
R
. Maximum
, with maximum
R
Baseline
The baseline
R
There is noted sex difference
Another moderating variable
A
is sex difference
R
Monaural
For acoustic stimuli, monaural
A
Response and reaction are affected by interval duration and attention.