If the response evoked by sounds presented to both ears are subtracted from the sum of the responses evoked by sounds presented to the left and the right ear (L + R - B), the binaural interaction component is derived. It seems it is related to spatial localization.
An explanation of this derived BIC is (Pratt, 2011) :
L = activity of left monaural neurons + activity of binaural neurons
R = activity of right monaural neurons + activity of binaural neurons
B = activity of left monaural neurons + activity of right monaural neurons + activity of binaural neurons
L + R = activity of left monaural neurons + activity of right monaural neurons + 2 * activity of binaural neurons
BIC = L + R - B = activity of binaural neurons
[left monaural neuron: neuron that is capable of responding only to left ear stimulation
right monaural neuron: neuron that is capable of responding only to right right stimulation
binaural neuron: neuron that is capable of responding to stimulation at either ear]
I feel this explanation is oversimplified. Is there a more complicated but reasonable model of the BIC? Where and how is binaural interaction produced? Are there monaural neurons and binaural neurons at every level of auditory system (AN, CN, SOC, LL, IC, MGB)?
I don't have a clear answer for the BIC question. However, regarding the latter part of the question about existence of binaural neurons at different levels int he auditory system, have you seen the Jefress Model ?
Regarding the BIC, in the scalp recorded AEP, I have written a manuscript related to it. If you are interested, I can send it to you.
Binaural interaction in many non-mammals begins at the level of the middle ear - see, e.g. Christensen-Dalsgaard, J., Manley, G.A. (2005) Directionality of the lizard ear. J. Exp. Biol. 208, 1209-1217. In the brain of the barn owl a study has revealed some differences that shed light on the underlying mechanism (see Palanca-Castan N, Laumen G, Reed D, Köppl C (2016) The binaural interaction component in barn owl (Tyto alba) presents few differences to mammalian data. JARO 17:577-589 and references therein).
I am not convinced of the value of binaural interaction. When I issued NHS hearing aids many years ago it was standard practice to only issue them to the one (better hearing) ear. I am puzzled that two aids are now the rule. There was never any great pressure from patients to have aids for both ears.
There was one memorable exception. A 75y old man insisted on binaural fitting. When I asked why, he said he needed them for his work, and he was in such demand he could not retire. He had moderate Meniere-type fluctuating hearing loss in both ears of totally different frequency profile plus likely diplacusis, so binaural fusion was implausible. Surely his ears must have been acting as independent units? His job -- Piano Tuner!
As Lutz and Geoff's references pointed out, the binaural neurons might not answer the same to monaural stimuli as compared to the binaural stimulus. Thus a corrected derivation for BIC would be
L = activity of left monaural neurons + activity of binaural neurons (to monaural L stimulus)
R = activity of right monaural neurons + activity of binaural neurons (to monaural R stim)
B = activity of left monaural neurons + activity of right monaural neurons + activity of binaural neurons (to binaural B stim)
L + R = activity of left monaural neurons + activity of right monaural neurons + activity of binaural neurons (L stim) + activity of binaural neurons (R stim)
BIC = L + R - B = activity of binaural neurons (L stim) + activity of binaural neurons (R stim) - activity of binaural neurons (B stim)
Thus BIC (as the name suggests) reveals the binaural interaction of the neurons as compared to the linear prediction from L + R monaural stimuli. Furthermore, BIC is not just the activity of the binaural neurons.
In response to the "Where" part of your question, it is now assumed that the BIC can be produced at different parts of the auditory system from the brain stem to the cortex. for more reading we recommend these two references:
Laumen, G., Ferber, A. T., Klump, G. M., & Tollin, D. J. (2016). The Physiological Basis and Clinical Use of the Binaural Interaction Component of the Auditory Brainstem Response. Ear and hearing, 37(5), e276-e290.
Henkin, Y., Yaar-Soffer, Y., Givon, L., & Hildesheimer, M. (2015). Hearing with two ears: Evidence for cortical binaural interaction during auditory processing. Journal of the American Academy of Audiology, 26(4), 384-392.
Thank all of you very much. Your messages are very helpful for my understanding of the BIC. : )
To expand on the 'where' aspect of your question, the canonical site of binaural integration in the central auditory system of mammals (both anatomically and functionally) is in the superior olivary complex (principally the medial and lateral superior olives and the medial nucleus of the trapezoid). I would recommend the work of Yin and colleagues to get started thinking out this. The following is a link to a good chapter that may help: Article Neural Mechanisms of Encoding Binaural Localization Cues in ...
Hi Xiaochen,
The lead article of a recent special issue of Biological Cybernetics dedicated to animals with ICE (Internally Connected Ears) might be useful to you as well:
Van Hemmen JL, Christensen-Dalsgaard J, Carr CE and Narins PM (2016) Animals and ICE: meaning origin and diversity. Biol Cyber 110: 237–246.
Peter
And one more reference I found interesting:
Grofova I. and Corvaja N. (1972). Commissural projection from the nuclei of termination of the VIIIth cranial nerve in the toad. Brain Res. 42: 189-195.
In this paper they demonstrate that the first binaural interaction in the toad brain occurs at the level of the dorsal medullary nucleus (the equivalent of the cochlear nucleus in the mammal). In mammals, the first neural binaural interactions occur in the superior olivary complex. I have always interpreted this as the importance for toads to extract binaural information as rapidly as possible.
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