Coincidence analysis of the effect of cochlear disparities on temporal responses to pure tones SfN 2011

1. Coincidence analysis of the effect of cochlear
disparities on temporal responses to pure tones
Philip X. Joris & Shotaro Karino
Lab. of Auditory Neurophysiology
Univ. of Leuven, Belgium
1. Single pair example 3. Population overview
Methods
Introduction
The convergence of neurons with different
characteristic frequency (CF) on a
postsynaptic target has been explored in
several models (Bonham and Lewis 1999;
Carney 1990; Carney et al. 2002; Schroeder
1977; Shamma 1989). We refer to such
convergence as monaural or binaural
cochlear disparities.
Cochlear disparities create interesting
properties, particularly at initial stages of the
auditory system where temporal coding of
sound waveforms occurs over a wide range
of frequencies. With current in vivo
techniques, it is difficult to simultaneously
measure pre- and postsynaptic physiological
properties, so that there have been few
empirical tests of the effects of cochlear
disparities. We examine the effect of such
disparities on responses to pure tones, using
a simple coincidence analysis.
• cats, barbiturate anesthesia
• auditory nerve fiber recordings with high
impedance micropipettes (sequential)
• closed, calibrated acoustic system
• spike timing at 1 μs
• stimuli: long duration (1000/1500 ms) pure
tones straddling the response area
• analysis: count coincidences across spike
trains of pairs of nerve fibers, for different
delays (cross correlograms)
TOP Coincidence counts (cross-correlograms) at different frequencies
MIDDLE Rate, Sync (vector strength), their product (SyncRate), and Phase for
individual fibers (blue) and for their coincidences (green)
BOTTOM Addition and superposition of coincidences at different frequencies
Effect of adding a pure time delay (1ms) and pure phase delay (0.2 cycle) on
pattern of coincidences. One fiber is compared with itself.
4. CD-CP relationship from cochlear disparities
2. Illustration of CD and CP
TOP Phase-frequency relationships for different ranges of CFs, pooled across
animals and SPLs. Red and green dots show CFs of each pair.
BOTTOM Same curves, with syncrate superimposed in color. Normalized to
maximum syncrate.
Scale of ordinate and abscissa is identical for all plots.
rate sync
phase syncrate
CF1 = 1207 Hz, SR = 1 spks/s
CF2 = 1466 Hz, SR = 2 spks/s
DCF = 0.28 oct, Cochlear distance = 0.79 mm
Conclusions
5. CD-CP relationship in inferior colliculus
4. Comparison
CD-CP relationship measured with linear regression
(weighted for rate), for 1 animal.
Pairs with maximal difference in CF of 0.1 octave.
CD-CP relationship in 4 animals, unsigned.
Maximal difference in CF was 0.3 octave.
CD-CP analysis for a binaural IC neuron (CF 1.9 kHz).
CD-CP relationship in IC. Color indicates best ITD.
Comparison of CD-CP relationship in IC (+)
with that expected from cochlear disparities (o).
• cochlear disparities create phase-
frequency relationships that contain
both group-delay and phase-delay
components
• phase-frequency relationships are
generally curved with a “bump” near CF
• cochlear disparities create and
inverse CD-CP relationship
• this relationship is reminiscent of that
seen in binaural responses in the IC
(Mc Alpine et al., 1996)
Supported by the Fund for Scientific Research – Flanders
(G.0714.09 and G.0961.11), and Research Fund
K.U.Leuven (OT/05/57 and OT/09/50).