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Enhancement of forward suppression begins in the ventral cochlear nucleus.

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Ingham, Neil J 
Itatani, Naoya 
Bleeck, Stefan 
Winter, Ian M 


A neuron׳s response to a sound can be suppressed by the presentation of a preceding sound. It has been suggested that this suppression is a direct correlate of the psychophysical phenomenon of forward masking, however, forward suppression, as measured in the responses of the auditory nerve, was insufficient to account for behavioural performance. In contrast the neural suppression seen in the inferior colliculus and auditory cortex was much closer to psychophysical performance. In anaesthetised guinea-pigs, using a physiological two-interval forced-choice threshold tracking algorithm to estimate suppressed (masked) thresholds, we examine whether the enhancement of suppression can occur at an earlier stage of the auditory pathway, the ventral cochlear nucleus (VCN). We also compare these responses with the responses from the central nucleus of the inferior colliculus (ICc) using the same preparation. In both nuclei, onset-type neurons showed the greatest amounts of suppression (16.9-33.5dB) and, in the VCN, these recovered with the fastest time constants (14.1-19.9ms). Neurons with sustained discharge demonstrated reduced masking (8.9-12.1dB) and recovery time constants of 27.2-55.6ms. In the VCN the decrease in growth of suppression with increasing suppressor level was largest for chopper units and smallest for onset-type units. The threshold elevations recorded for most unit types are insufficient to account for the magnitude of forward masking as measured behaviourally, however, onset responders, in both the cochlear nucleus and inferior colliculus demonstrate a wide dynamic range of suppression, similar to that observed in human psychophysics.



Auditory, Brainstem, Context, Guinea pig, Masking, Acoustic Stimulation, Action Potentials, Algorithms, Animals, Auditory Pathways, Auditory Threshold, Choice Behavior, Cochlear Nerve, Cochlear Nucleus, Guinea Pigs, Inferior Colliculi, Microelectrodes, Neurons, Signal Processing, Computer-Assisted

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Brain Res

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Elsevier BV
This work was supported by Wellcome Trust and BBSRC Project Grants to IMW and first presented in preliminary form by Ingham et al. (2006b). We thank Elinor Gunning and Catherine Slattery for their help and input during pilot experiments and Mark Sayles for help in data collection in later experiments.