Modeling Responses in the Superior Paraolivary Nucleus: Implications for Forward Masking in the Inferior Colliculus

Abstract

A phenomenological model of the responses of neurons in the superior paraolivary nucleus (SPON) of the rodent is presented in this study. Pure tones at the characteristic frequency (CF) and broadband noise stimuli evoke offset-type responses in these neurons. SPON neurons also phase-lock to the envelope of sinusoidally amplitude-modulated (SAM) stimuli for a range of modulation frequencies. Model SPON neuron received inhibitory input that was relayed by the ipsilateral medial nucleus of the trapezoid body from the contralateral model ventral cochlear nucleus neuron. The SPON model response was simulated by detecting the slope of its inhibitory postsynaptic potential. Responses of the proposed model to pure tones at CF and broadband noise were offset-type independent of the duration of the input stimulus. SPON model responses were also synchronized to the envelope of SAM stimuli with precise timing for a range of modulation frequencies. Modulation transfer functions (MTFs) obtained from the model response to SAM stimuli resemble the physiological MTFs. The output of the proposed SPON model provides an input for models of physiological responses at higher levels of the ascending auditory pathway and can also be utilized to infer possible mechanisms underlying gap detection and duration encoding as well as forward masking at the level of the auditory midbrain.

Rate and synchrony at the level of the auditory nerve are not sufficient to account for behaviorally estimated cochlear compression - a modeling study

“…Interestingly, such inhibition at the IC level was shown to be diminished after acoustic trauma resulting in hearing impairment (Wang et al 2002). A similar modeling analysis as presented here including neurons from more central stages (cochlear nucleus (CN), IC, SPON) (Salimi et al 2017) could shed light on the underlying mechanisms of TMCs and forward masking and their potential use to estimate BM compression.…”

Responses of neurons in the rat’s inferior colliculus to a sound are affected by another sound in a space-dependent manner

“…Thus, an inhibitory aftereffect can be generated by a leading contralateral sound through the superior paraolivary nucleus to inhibit the response of an IC neuron to a trailing contralateral sound. This inhibitory aftereffect likely plays a key role in generating forward masking 58–60 . Over a two-tone sequence with both sounds (T L and T H ) presented at c90°, each of the 200 stimuli could have produced an inhibitory effect on an IC neuron through the superior paraolivary nucleus, which could have decreased mean responses elicited by both sounds.…”

Inherent envelope fluctuations in forward masking: Effects of age and hearing loss

“…To date, computational models of the auditory system have not been used to clarify possible physiological mechanisms associated with GN disruption. However, computational models have been used extensively to examine mechanisms associated with forward masking (Dau et al, 1996;Derleth et al, 2001;Meddis and O'Mard, 2005;Nelson and Young, 2010;Gai, 2016;Salimi et al, 2017). The auditory models used thus far have included various properties of the auditory system, including the compressive nonlinearity, filtering of the cochlea, adaptation of the auditory nerve, and modulation filtering within the central auditory system (e.g., Derleth et al, 2001).…”

“…and Salimi et al (2017) attempted to model properties of the IC, only Meddis and O'Mard attempted to predict behavioral performance. In contrast, Salimi and colleagues attempted to model rate-level functions for growth of masking.…”