Habituation of Auditory Evoked Potentials: The Dynamics of Waveform Morphology

Habituation of auditory evoked potentials is central to our understanding of the processes of attention within the auditory neuronal pathways and clinical applications in audiological diagnosis. This study presents a unique methodology to elaborate on auditory habituation over time with the acquisition of evoked potentials. Subjects were presented with clicks at a rate of 1 per second for 90 min. Each subject listened to a total of 5400 click stimuli (trials). A time epoch of 500 ms was used and each trial was digitised at a sample rate of 12,800 samples per second. The trials were individually saved and 4401 evoked potentials were obtained offline using a moving average of 1000 trials (1-1000; 2-1001, and so on). A unique paradigm was developed, which allowed the early, middle and late components of the auditory evoked potential to be acquired simultaneously and also permitted the study of amplitude and latency interdifferences between the evoked potentials in order to observe the progression of habituation. Amplitude changes occurred as the subject progressed through various states of alertness and attentiveness. The results of the study indicated that the habituation process modulates the waveform at different response latencies over a 90 minute time period. Similar patterns were found for all subjects in the sample. The habituation was found to be the greatest for the late evoked potentials, in agreement with the involvement of higher order functioning related to structures such as the frontal cortex and auditory regions of the hippocampus. The middle latency components were also found to be affected by the process of habituation, with visible amplitude and latency changes, while only modest changes were observed in the auditory brainstem response components over the 90 minute time period. This implies that within the auditory pathway and the entire auditory evoked potential there is a follow on or cumulative effect of habituation that increases within the sampled time epoch during auditory habituation and attention fluctuations.