Sensory gating of auditory evoked potentials in rats: effects of repetitive stimulation and the interstimulus interval

In the P50 gating or conditioning-testing (C-T) paradigm, the P50 response, a small positive midlatency ( similar to 50 ms after stimulus onset) compo nent of the human auditory evoked potential (AEP), is reduced towards the s econd click (S2) as compared to the response to the first click (S1). This phenomenon is called sensory gating. The putative function of sensory gatin g is thought to protect subjects from being flooded by irrelevant stimuli. Comparative studies have been done in rats in order to elucidate the underl ying neural substrate of sensory gating. However, for a direct comparison o f rat and human AEP components, it is imperative for both components to sho w similar characteristics. The amount of sensory gating in humans is depend ent on repetitive stimulation and the interstimulus interval (ISI). In the present study effects of repetitive stimulation (Experiment 1) and various ISIs (Experiment 2) were determined on rat AEP components. The results demo nstrate that gating is not limited to a restricted cortical area or a singl e midlatency component and that repetitive stimulation and ISI affect gatin g of several rat AEP components. Components such as the vertex P17 and N22 show a decrease in gating within several S1-S2 presentations, mainly due to a decrease in amplitude to S1 (Experiment 1). Gating for vertex components (such as the P17, N22 and N50) is ISI dependent (Experiment 2), but there is no interval in the 200-600 ms range at which optimal gating occurs. The ISI effects on gating are due to an increase of the amplitude to S2. The re sults have implications for the discussion about the rat homologue of the h uman P50. (C) 2001 Elsevier Science B.V. All rights reserved.