The effects of digital filtering on feline auditory brain-stem evoked potentials

Abstract

The power spectrum of the feline auditory brain-stem evoked potentials (ABEPs) consists of 3 frequency bands, similar to the human wave form, but differing in range. The frequency bands in the feline spectra were separated by notches at 326 Hz and 732 Hz. Click-evoked ABEP from 15 cats were digitally filtered in 3 passbands: (1) below 326 Hz (‘slow filter’), (2) between 326 and 732 Hz (‘medium filter’); and (3) between 732 and 1790 Hz (‘fast filter’). Filtering in each of these bands differentially affected the ABEP components. The vertex positive components are labeled by their order of appearance, i.e., 1, 2,...5. Peak 1 is subdivided into 2 subcomponents labeled 1a and 1b. The slow filter was associated with the loss of all components leaving a slow potential shift, i.e., the ‘pedestal’ peaking at the latency of peak 4. The medium filter was associated with the loss of components 1a, 1b and 2, sparing 3 and 4. The fast filter was associated with the loss of 1b and a diminution of 2. Comparing cat and human ABEP, feline components 2, 3 and 4 behaved precisely the same as the human II, III and V. In contrast to the human I, the feline first component (1a) was not detected with the medium filter. No feline component, following peak 1 in the unfiltered wave form, disappeared with the slow and medium filters, and reemerged with the fast filter (as human IV does). Thus, based on the effects of digital filters on ABEP wave form, the human peak IV did not have a feline counterpart, and the feline bifid peak 1 differed compared to its human I counterpart. Some of these conclusions run counter to homologues suggested from lesion and depth recording experiments. Factors related to differences in the dimensions, composition, and orientation (relative to the recording electrodes) of the auditory pathway of humans and cats could affect the definition of homologues between the two species using filters as well as lesion and depth recordings.