Chapter 4

Notes  (19 Aug 2008)

P. 73: The numbers of synapses and hair cells contacted depends on cochlear position and, for OHCs, on the row of OHC. Basal IHCs have numbers of synaptic contacts at the upper end of the range quoted in the text (30), and apical IHCs the lower number (10) (in the cat: Liberman et al., 1988). In contrast, each OHC has fewer synaptic contacts with afferent fibres in the base (5 – 8 depending on row), and more in the middle and apical turns (15 – 19 in middle turn, 9 – 17 in apical turn; cat, Simmons and Liberman, 1988). Each OHC in Row 3 (the row furthest away from the modiolus) receives twice as many afferent endings as each OHC in Row 1 (nearest to the modiolus). Similarly, each apical fibre to OHCs makes synaptic contacts with a greater number of OHCs in the apex than in the base, and with more OHCs in row 3 than in row 1. (16 Aug 2008).

P. 89: The reverse correlation technique, and the first-order Wiener kernel, are only of value if the stimulus frequency is in the range for phase locking. At higher frequencies, the techniques do not work. However, a fibre can of course still show increases in short-term average firing rates, to stimuli with frequencies above the limit for phase locking. An increase in mean firing rate can be thought of as the product of a square-law distortion, in the inner hair cell input-output function, in the synapse, and in the action potential generator. The responses to high frequency stimuli can therefore be extracted from the second order Wiener kernel (Recio-Spinoso et al., 2005). However here, because the method depends on finding increases in the short-term mean firing rate, it cannot be used at medium and high intensities when the firing is saturated.

A further interesting method of using temporal information to measure auditory nerve fibre responses is that of measuring phase locking to the low-frequency beats that occur between the tones of a high frequency multitone complex that is used to stimulate the fibre (van der Heijden and Joris, 2003, J. Neurosci. 23: 9194-9198). This method gives relative amplitudes and phases of the tone response, up to the highest frequencies of stimulation.
(16 Aug 2008).

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