Distinct forms of prepulse inhibition disruption distinguishable by the associated changes in prepulse-elicited reaction

Prepulse inhibition (PPI) of the acoustic startle reflex has been extensively employed as a test of sensorimotor gating or early attentional control in neuropsychiatric research, because a number of psychiatric conditions, including schizophrenia, exhibit PPI deficiencies. In both human and animal studies, PPI is commonly demonstrated by an attenuation of the acoustic startle reflex when the startle-inducing pulse stimulus is shortly preceded by a weak non-startling prepulse stimulus. This weakening of the startle reaction is attributed to, and therefore also provides an indirect measure of, the inhibition triggered by the perception of the prepulse stimulus. The relative ease in measuring the overt pulse-elicited startle reaction, in comparison with the relatively weak prepulse-elicited reaction (PPER) has led to a near complete neglect of the latter in recent literature. However, the assumption that the prepulse used in PPI is non-startling, does not imply that it is associated with no measurable responses. In fact the feasibility and reliability of obtaining such measures has been confirmed in both rodents and humans, and here we review the key findings derived from the direct evaluation of prepulse-elicited reaction in PPI, including under conditions that lead to PPI deficits. The theoretical implications and potential interpretative values of PPER are discussed. It is concluded that PPER should no longer be ignored; its emphasis may shed light on the kind of inhibition or gating dysfunction relevant to PPI disruption seen in pathological conditions including schizophrenia.