Inhibitory processes are often studied with a double click paradigm. The amount of inhibition (gating) is determined by a ratio or difference score. In the present experiment the relation between the interstimulus interval (ISI) and the amount of gating was investigated.
Method: Twelve adult male Wistar rats were chronically equipped with a permanent EEG electrodes with an active electrode at the vertex. After habituation to the stimuli, eight blocks of double clicks (96 dB) with different ISI's (range 200 - 5000 msec) were presented in counterbalanced order. Minimally 100 auditory evoked potentials (AEP) were averaged for each ISI.
Results: The AEP consisted of several components, e.g. a P20 and P50. Gating was found for the P20 (F7,63=2.37, p<0.05) and the P50 (F7,63=7.44, p<0.001), not for the negative components. Both components showed only gating at ISI's between 200 and 1000 msec.
Conclusions: Gating in rats occurs but not for all components of the AEP: the positive components show more gating than the negative ones. Furthermore, the ISI seems crucial for gating: it occurs only at ISI's of 1 sec or shorter. In all cases it is rather amazing that a neutral and fully habituated stimulus is able to reduce certain components of a second AEP for a time period as long as one second. Interestingly, this inhibitory process seems to be disturbed in 90% of the schizophrenic population.
Referat in der Gruppe Klinische Psychologie, Dienstag, 30. März 1999, 08:30, HS 14
