Relationship between PPI and baseline startle response

Abstract

Prepulse inhibition (PPI) of the startle response to a sudden noise is the reduction in startle observed when the noise is preceded shortly by a mild sensory event, which is often a tone. A part of the literature is based on the assumption that PPI is independent of the baseline startle. A simple model is presented and experimental validation provided. The model is based on the commonly accepted observation that the neuronal circuit of PPI differs from that of startle. But, by using a common output, the measures of both phenomena become linked to each other. But, how can we interpret the numerous experimental data showing PPI to be independent of the startle level? It is suggested that in a number of such cases the baseline startle would have been stabilized by a ceiling effect in the startle/PPI neuronal networks. Reducing the startle level, for example in a PPI evaluation procedure, may disclose properties of startle masked by this ceiling effect. Disclosure of habituation to the startle eliciting noise produced an increase of PPI along its initial measurements. Taken together, even if the neuronal process that sustains startle and PPI are distinct, separating them experimentally requires careful parametric methods and caution in the interpretation of the corresponding observations.

On the influence of baseline startle reactivity on the indexation of prepulse inhibition.

“…Moreover, although many studies do not find a significant correlation between startle reactivity and %PPI, there are indeed positive findings for such a dependency, although the correlations explained only a limited proportion of the variance (Blumenthal et al 2004;Ison et al 1997;Yee et al 2005). Nevertheless, based on the data from animal studies Sandner and Canal (2007) suggested a neural network model of sensorimotor gating in which %PPI decreased with increasing startle amplitude, and a similar model has been proposed by Schmajuk and Larrauri (2005).…”

Are DBA/2 mice associated with schizophrenia-like endophenotypes? A behavioural contrast with C57BL/6 mice

“…This is of significant concern because differences in the baseline startle reactivity can seriously complicate or confound the interpretation of the results obtained on PPI (Csomor et al 2006(Csomor et al , 2008Hoffman and Searle 1965;Swerdlow et al 2000;Yee et al 2005). The dependency of PPI magnitude on baseline startle reactivity has been demonstrated in rodents and humans (Csomor et al 2006(Csomor et al , 2008Hince and MartinIverson 2005;Yee et al 2005)-a finding that has been incorporated also by computational models of PPI (Sandner and Canal 2007;Schmajuk and Larrauri 2005). The present study was undertaken to initially address the confounding phenotype on startle reactivity in comparison with C57BL/6 mice using a more stringent parametric design of PPI assessment incorporating multiple pulse intensities (Csomor et al 2006(Csomor et al , 2008Yee et al 2005).…”

Noise benefit in prepulse inhibition of the acoustic startle reflex

“…The noise-PPI response therefore appears to be left-shifted in SH rats compared to Wistar and Sprague-Dawley rats. Because a strain with low baseline ASR will display a higher percentage PPI than a strain with a high baseline ASR, given that the absolute inhibition is similar in both strains (Csomor et al 2008;Sandner and Canal 2007), we decided to rule out the possibility that strain×noise level interaction emerged only as a result of covariance of baseline startle reactivity and PPI. Including the baseline startle reactivity [mean ASR for background noise levels 55-67 dB(A)] as a covariate in the analysis revealed that significant interaction between strain and noise level remained.…”