Hi Daniel,

There two type of nerve cell in auditory nerve. Type I are connected to inner hair cells (IHC) and type II to outer hair cells (OHCs). Nerve cells can be divided in categories according to different characteristics: saturation rates, sensitivity... These characteristics may determined a best frequency answer all along the cochlea.

Phase locking could be defined as the ability for a nerve cell to phase locked hair cell synaptic activity to its APs firing rate. Best regards, Julien

Daniel

There are two ways the frequency of a sound can be coded in the auditory nerve: by place or by time. Place refers to the fact that the individual hair cells along the basilar membrane are stimulated differently, depending on the frequency of the sound. This is due to the changing biomechanical properties of the basilar membrane (stiffness and width being most important) and electrical tuning of the individual hair cells. This results in individual fibers in the auditory nerve carrying information about energy at specific frequencies, reflecting the position of the hair cell the nerve fibre has contact with. Inner hair cells, which are the receptor cells have connections to many fibres, but each fiber only innervate one hair cell. Outer hair cells have a role in sharpening the mechanical tuning of the basilar membrane and are not directly involved in coding of the sound into neural signals..

Time coding refers to phase locking. For low frequencies, the hair cells may fire preferentially at the peaks of the signal, making them fire with a rate equal to the frequency of the signal, if it is a sine wave, i.e. one spike (or one group of spikes) for each period of the sine wave. This only works up to frequencies up to 1-2 kHz at the very most, as the nerves are not capable of firing at higher rates. Ensemble coding has been proposed as a mechanism at higher frequencies, where each fiber would only fire to say on average every 5th period of the signal but given enough independent fibres, the sum of the activity would still carry phase information. Difficult to see how it can be decoded, though, as the neurons in the auditory centres of the brain have the same (or even poorer) capability to fire at high rates.

Jakob

Thanks a lot, was explained a bit confusing to me in lecture script...

Sounds very interesting. Maybe I can include this somewhere in my master thesis. I'd like to take a look at your poster, please contact me.

Maybe it's just been to much text, but what do you want to know?

The only thing I found is the influence of radii ratio: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2299218/

It's really interesting, but as human's cochlear doesn't vary in radii ratio that much, this should be neglectable.