Contralateral single neuron receptive fields in the mammalian cochlear nucleus

Ingam, Neil, Bleeck, Stefan and Winter, Ian (2005) Contralateral single neuron receptive fields in the mammalian cochlear nucleus. ARO Meeting, New Orleans, USA. 19 - 24 Feb 2005. p. 133 .

Abstract

Wideband inhibition can improve the detection of signals in amplitude-modulated noise [eg Neuert et al 2004 J Neurosci 24: 589-9] when both signal and noise are presented ipsilaterally. Improvements in ipsilateral signal detection have been demonstrated psychophysically when noise is presented contralaterally. Here, we measure the effect of changing the frequency and level of a contralateral tone on single neurons in the guinea-pig cochlear nucleus. Pure tone receptive fields were recorded (n=58) using combinations of monaural and binaural stimuli. Many neurons showed no evidence of neural responses originating from the contralateral ear (n=25). However, 2 neurons responded with activity patterns that were suggestive of contralateral inhibitory input. In several cases (n=10), the inhibition was evident at relatively high contralateral stimulus levels and at frequencies below the ipsilateral best frequency (BF); "off-BF inhibition". For the remainder (n=1), the contralateral tone evoked an inhibitory pattern which produced a "negative" of the ipsilateral excitatory receptive field. In many cases, this inhibition extended to low stimulus levels, close to the threshold stimulus level for an ipsilateral tone; "on-BF inhibition". A few neurons (n=6) exhibited responses consistent with excitatory input from the contralateral ear. Our results are in agreement with previously published studies of the cochlear nucleus [Mast 190 J Neurophys 33: 108-15; Mast 193 Br Res 62: 61-0; Joris & Smith 1998 J Neurosci 18: 1015-0; Shore et al 2003 Exp Brain Res 153: 42-35]. We have extended these studies into the domain of the pure tone receptive field, where the relative inhibitory/excitatory strength as a function of both frequency and level can be assessed. These preliminary data suggest that the improvement of signal detection in noise at the level of the cochlear nucleus may be reduced if the noise is presented to the contralateral ear. Supported by the Wellcome Trust.

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Contributors

Author: Stefan Bleeck

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