Article Figures & Data
Figures
- Figure 1.
A, Representative image of a hematoxylin and eosin stained midmodiolar section from a rat cochlea showing the two locations indicated by the dashed lines at which the spiral ganglion neurons (SGNs) were stimulated by the apical and basal bipolar electrode pairs, respectively (20×). B, Representative images of the SGNs in the apical and basal turns for the normal controls and neonatally deafened (ND) animals (40×). C, Mean SGN densities at two different cochlear locations for the normal controls and ND animals. Error bars represent ±1 SD.
- Figure 2.
A, Temporal discharge pattern (dot rasters) of an example neuron for 40-pps pulse trains as a function of the interaural time difference (ITD). B, The mean spike count for the entire stimulus duration of 300 ms as a function of the ITD (dashed line). Error bars indicate ±1 SD. To smooth out noise in ITD tuning curve, both the mean (thick blue line) and the variance (light blue shade) of the spike count were fitted with a cubic spline. C, Standard separation (D) curves for two different reference ITD (blue line for 0 μs and orange line for −100 μs) as a function of ΔITD (difference from a reference ITD). ITD JNDs (arrow) at each reference ITD are where D = 1 (black dashed horizontal line). D, Neural ITD JND curve as a function of a reference ITD within the physiological range of ITD (±160 μs). The smallest value of 202 μs is determined as the ITD JND of an example neuron.
- Figure 3.
A–C, Temporal discharge pattern (dot rasters) to 20-, 40-, and 80-pps pulse trains as a function of the interaural time difference (ITD) for an example apical unit from a neonatal deafened rat. Signal-to-total variance ratio (STVR) values and corresponding p-value from the F test are presented for three different time segments (total responses for 0–300 ms; and sustained responses for 20–300 ms). D, Firing rate of total responses versus ITD curves for a range of pulse rates for the same example neuron.
- Figure 4.
Percentage of apical and basal units with interaural time difference (ITD) sensitivity as a function of the pulse rate in acutely deafened (AD; solid lines) animals and neonatally deafened (ND; dashed lines) animals.
- Figure 5.
Interaural time difference (ITD) signal-to-total variance ratio (STVR) as a function of pulse rates in acutely deafened (AD) animals and neonatally deafened (ND) animals to apical (A) and basal pair stimulations (B). The central black dot inside a white circle indicates the median, and the bottom and top edges of the box present the 25th and 75th percentiles, respectively.
- Figure 6.
Interaural time difference (ITD) signal-to-total variance ratio (STVR) at various pulse rates for apical and basal units based on responses for different time segments, including total (0–300 ms; A) and sustained (20–300 ms; B), in neonatally deafened (ND) rats. The central black dot inside a white circle indicates the median, and the bottom and top edges of the box present the 25th and 75th percentiles, respectively. C, ITD just noticeable difference (JND) versus the pulse rate from individual units for apical and basal stimulations. The area of the circles at the top is proportional to the number of units with unmeasurable (UM) JNDs. The dotted, solid, and dashed lines represent the 12.5th, 25th, and 50th percentiles, respectively. The horizontal black dashed line illustrates the maximum ITD difference in adult rats (320 μs).
- Figure 7.
Distribution of interaural time difference (ITD) tuning types according to the location of stimulation for acutely deafened (AD) and neonatally deafened (ND) animals.
- Figure 8.
Distribution of ITD at the maximum slope (ITDMS) for apical (A, C) and basal (B, D) stimulation in neonatally deafened (ND) and acutely deafened (AD) groups. The vertical dashed lines indicate the physiological ITD range of the rat (±160 μs).
- Figure 9.
Temporal response patterns to 80 pps electrical pulse trains as a function of the interaural time difference (ITD) for one apical unit (A) and one basal unit (B). Both example neurons have a monotonic ITD tuning type and similar ITD signal-to-total variance ratio (STVR) at 80 pps. C, ITD tuning curves at 80 pps for the two example neurons. The arrows indicate the maximum slope position of the ITD tuning curve. The vertical dashed lines illustrate the physiological ITD range (±160 μs). D, Distributions of ITD at the maximum slope (ITDMS) for monotonic type units for apical and basal stimulation in neonatally deafened animals.
Tables
- Table 1
Distribution of ITDMS by the ITD tuning type for apical and basal stimulation in neonatally deafened animals
ITD tuning type Percentage of units (%) Peak Monotonic Trough Unclassified Apical units ITD-sensitive unitsa (n = 52) 40.4% (21/52) 42.3% (22/52) 15.4% (8/52) 1.9% (1/52) |ITDMS| ≤160 μsb (n = 23) 38.1% (8/21) 45.5% (10/22) 62.5% (5/8) N/A ITDMS (μs)c 56 ± 295 (−438 to 688) 34 ± 325 (−703 to 736) −58 ± 308 (−676 to 313) N/A Basal units ITD-sensitive unitsa (n = 28) 25.0% (7/28) 67.9% (19/28) 3.6% (1/28) 3.6% (1/28) |ITDMS| ≤ 160 μsb (n = 6) 28.6% (2/7) 21.1% (4/19) 0% (0/1) N/A ITDMS (μs)c 27 ± 239 (−222 to 332) 78 ± 574 (−801 to 1200) 454 N/A Hancock et al. (2010) Hancock et al. (2013) Thompson et al. (2021) Chung et al. (2019) This work Species Cats Cats Cats Rabbits Rats Deafening procedure Congenitally deaf Congenitally deaf Neonatal deafening (neomycin sulfate) Neonatal deafening (neomycin sulfate) Neonatal deafening (kanamycin) Approaches for implant insertion Round window Round window Round window Round window Cochleostomies Electrodes 8-ring electrode array 8-ring electrode array 8- or 14- ring electrode array 8-ring electrode array 4 independent electrodes Stimulus configuration Wide bipolara Wide bipolara Wide bipolara Wide bipolara Scala tympani and scala vestibuli electrodes pair Pulse rates (pps) 10–80 10–80 40 20–1280 20–1280 Phase duration and interphase gap (μs) 50/0 50/0 100/50 50/0 40/0 Analysis metric of ITD sensitivity STVR
(F test, p < 0.025)STVR
(F test, p < 0.025)STVR
(F test, p < 0.025)STVR
(F test, p < 0.01)STVR
(F test, p < 0.01)Incidence of ITD sensitivity (no. of units) 48% (114) 53% (139) 56% (55) 62% (66) 65% (100)
55% (100)b
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