Unrecognized errors due to analog filtering of the brain-stem auditory evoked response

Area of Science:

• Neuroscience
• Signal Processing
• Auditory Neuroscience

Background:

• Analog filtering is commonly applied to electrophysiological signals like the brain-stem auditory evoked response (BAER).
• Steeply sloped filters are often used to isolate specific frequency components.
• Potential for filter-induced artifacts in BAER analysis is not fully understood.

Purpose of the Study:

• To investigate the distortion effects of analog filtering on brain-stem auditory evoked responses (BAERs) and synthetic waveforms.
• To identify appropriate bandpass frequencies for accurate BAER analysis in rats.
• To explain cross-laboratory variability in BAER recordings.

Main Methods:

• Analysis of analog filter transfer functions (gain and phase) across frequencies.
• Filtering of synthetic waveforms to demonstrate distortion.
• Spectrum analysis of typical Long-Evans rat BAER waveforms.
• Evaluation of filter effects on peak identification and waveform integrity.

Main Results:

• Steeply sloped analog filters cause significant waveform distortion, even with cut-off frequencies outside the signal spectrum.
• Filter-induced distortion can lead to erroneous peak identification, including potential reversal of peak order.
• Filter artifacts were identified as a primary cause of variability in BAERs recorded across different laboratories.
• High-pass filtering at frequencies as low as 1/4 of the lowest constituent frequency can induce substantial distortion.

Conclusions:

• Analog filter selection critically impacts BAER waveform fidelity and interpretation.
• Careful consideration of filter characteristics is essential to avoid misinterpreting BAER data.
• Understanding filter-induced distortions is crucial for standardizing BAER recordings and reducing inter-laboratory variability.
• Recommendations for appropriate bandpass filtering are provided for rat BAER analysis.