SINGLE-TRIAL LATENCY VARIABILITY DOES NOT CONTRIBUTE TO FAST HABITUATION OF THE LONG-LATENCY AVERAGED AUDITORY-EVOKED POTENTIAL IN THE ALBINO-RAT

Fast habituation (FH) is defined as a general reduction in long-latenc y, vertex-recorded, averaged auditory evoked potential (AEP) amplitude that occurs in response to the second of a pair of acoustic stimuli. Our laboratory has been studying FH in a variety of human populations with different paradigms and has interpreted it to be a measure of neu ral attentional mechanism(s) and/or resource allocation related to the processing of cognitive information. We have also reported an analogo us phenomenon in the rat, In the present investigation, we examined th e relationship between FH (viz., averaged AEP component amplitude decr ement) and the single-trial latency variability of the AEP peaks compr ising that component. Specifically, AEPs were obtained to 60 paired-to ne stimuli from unanesthetized and restrained albino rats previously i mplanted with chronic skull electrodes. Using a template-matching algo rithm similar to that used by Michalewski et al. (Electroenceph. clin. Neurophysiol., 1986, 65: 59-71), the latency variability for each ani mal was computed for the N1 and P2 peaks of the single-trial AEPs that were used to compose the averaged wave form. Findings indicated that (a) there was no difference in single-trial latency variability for th ese peaks either within or across tones, and (b) there was no relation ship between single-trial latency variability for either the N1 or the P2 peaks and the overall peak-to-peak amplitude (N1-P2) of the averag ed wave form in response to the second tone. Thus, FH of the N1-P2 (i. e. Peak 2) amplitude in the rat is not due to an increase in latency v ariability across tones.