Spectra of Auditory Brainstem Responses and Spontaneous EEG

Human auditory brainstem responses (ABR´s) are sensory evoked potentials that can be recorded within a few milliseconds following a transient acoustic stimulus. This paper describes results of a simulation study that evaluated alternative techniques for estimating the spectrum of the ABR signal and of the background EEG. The effects of residual noise in the average signal, the number of responses in the average, and the use of smoothing windows were considered. Spectra of human ABR´s were also obtained. The spectral energy decreases with frequency to 2 kHz and seems to flatten above 2 kHz. The ABR signal spectrum is limited to below approximately 1.5 kHz. There are three main components: a low-frequency component around 100 Hz, a midfrequency component around 500 Hz, and a high-frequency component at 1000 Hz. Narrow-band filtering suggests that the midfrequency component is primarily associated with Jewett wave V, while the high-frequency component is primarily associated with the early Jewett waves. These two components are probably the most important for determining the latencies of waves. The low-frequency component appears to correspond to a slow wave on which the Jewett waves are superimposed.