P_b(P₁) resonance at 40 Hz: Effects of high stimulus rate on auditory middle latency responses (MLRs) explored using deconvolution

Objective: In this study, the effects of high stimulus rate on middle latency response (MLR) components P_a and P_b (P₁ or P50) were studied using high rate clicks in normal hearing awake subjects were investigated. Methods: Five jittered click sequences at different mean rates (24.4, 39.1, 58.6, 78.1, 97.7 Hz) were presented to 10 subjects. Overlapping MLRs were deconvolved using the frequency domain continuous loop averaging deconvolution (CLAD) [Özdamar Ö., Bohórquez, J., Signal to noise ratio and frequency analysis of continuous loop averaging deconvolution (CLAD) of overlapping evoked potentials. J. Acoust. Soc. Am., 119:429-438, 2006]. In addition conventional auditory transient MLRs at 4.88 Hz were obtained using conventional averaging. Results: P_a amplitude, latency and waveshape remained fairly constant up to 78.1 Hz. P_b component, however, showed a variable waveshape with latencies covering a wide range (50-70 ms) and N_b-P_b amplitudes increasing at 39.1 and 58.6 Hz and decreasing at other rates. Conclusions: Recordings show that both P_a and P_b MLR components can be consistently recorded at all rates up to 100 Hz. P_b amplitude shows an increase at around 40 Hz showing a resonance at that frequency. Significance: The dramatic increase of the P_b component at around 40 Hz may account for the high amplitude of the 40 Hz ASSR.