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Forward masking in the medial nucleus of the trapezoid body of the rat


Perception of acoustic stimuli is modulated by the temporal and spectral relationship between sound components. Forward masking experiments show that the perception threshold for a probe tone is significantly impaired by a preceding masker stimulus. Forward masking has been systematically studied at the level of the auditory nerve, cochlear nucleus, inferior colliculus and auditory cortex, but not yet in the superior olivary complex. The medial nucleus of the trapezoid body (MNTB), a principal cell group of the superior olive, plays an essential role in sound localization. The MNTB receives excitatory input from the contralateral cochlear nucleus via the calyces of Held and innervates the ipsilateral lateral and medial superior olives, as well as the superior paraolivary nucleus. Here, we performed single-unit extracellular recordings in the MNTB of rats. Using a forward masking paradigm previously employed in studies of the inferior colliculus and auditory nerve, we determined response thresholds for a 20-ms characteristic frequency pure tone (the probe), and then presented it in conjunction with another tone (the masker) that was varied in intensity, duration, and frequency; we also systematically varied the masker-to-probe delay. Probe response thresholds increased and response magnitudes decreased when a masker was presented. The forward suppression effects were greater when masker level and masker duration were increased, when the masker frequency approached the MNTB unit’s characteristic frequency, and as the masker-to-probe delay was shortened. Probe threshold shifts showed an exponential decay as the masker-to-probe delay increased.

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The authors wish to thank Dr. Alexandra Kadner for assistance with data analysis and interpretation, and for pre-submission critiques of the manuscript. We also thank Dennis Cole for help with histological localization of recording sites. This work was supported by NIH/National Institute on Deafness and Other Communication Disorders Grant RO1 DC-002266 to A. S. Berrebi. The authors have no conflict of interests to declare.

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Correspondence to Albert S. Berrebi.

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Gao, F., Berrebi, A.S. Forward masking in the medial nucleus of the trapezoid body of the rat. Brain Struct Funct 221, 2303–2317 (2016).

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  • MNTB
  • Auditory scene analysis
  • Context dependence
  • Forward suppression