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1.
Figure 12

Figure 12. Chopper units in tinnitus animals do not show elevated tone-responses. From: Noise over-exposure alters long-term somatosensory-auditory processing in the dorsal cochlear nucleus – possible basis for tinnitus-related hyperactivity?.

(A) Population RLFs and (B) PSTHs. For details see legend of . The elevation of rates for no-tinnitus animals was not significant. Tinnitus: n=3 animals / 15 units, no-tinnitus: n=2 animals / 19 units, control: n=5 animals / 23 units.

Susanne Dehmel, et al. J Neurosci. ;32(5):1660-1671.
2.
Figure 6

Figure 6. Effect of noise exposure on supratheshold tone discharge rates. From: Noise over-exposure alters long-term somatosensory-auditory processing in the dorsal cochlear nucleus – possible basis for tinnitus-related hyperactivity?.

Mean RLFs recorded at unit CF (−0.1 up to 0.0 octaves around CF) and below/above CF. RLFs of units with all CFs pooled. Control animals (black symbols, below CF : n=8 animals / 84 RLFs, at CF: n=8 animals / 50 RLFs, above CF: n=9 animals / 118 RLFs) are compared to noise-exposed animals (white symbols, below CF: n=11 animals / 153 RLFs, at CF: n=11 animals / 109 RLFs, above CF: n=11 animals / 201 RLFs).

Susanne Dehmel, et al. J Neurosci. ;32(5):1660-1671.
3.
Figure 1

Figure 1. Schematic of the gap detection test. From: Noise over-exposure alters long-term somatosensory-auditory processing in the dorsal cochlear nucleus – possible basis for tinnitus-related hyperactivity?.

The startle noise pulse elicits a startle movement of the guinea pig (top row), that is reduced when a gap in the background noise band is preceding the startle noise pulse (middle row). Tinnitus that is spectrally similar to the background noise masks the gap and increases the startle movement (bottom row), as the animals cannot detect the gap ().

Susanne Dehmel, et al. J Neurosci. ;32(5):1660-1671.
4.
Figure 11

Figure 11. Buildup units in tinnitus animals show elevated tone-responses. From: Noise over-exposure alters long-term somatosensory-auditory processing in the dorsal cochlear nucleus – possible basis for tinnitus-related hyperactivity?.

(A) Population rate level functions and (B) PSTHs of buildup units in control animals (black plots) and noise-exposed animals that developed tinnitus (white plots) and those that did not develop tinnitus (gray plots). PSTHs are shown for 10, 50, 80 dB. Tinnitus: n=2 animals / 7 units, no-tinnitus: n=2 animals / 16 units, control: n=5 animals / 11 units.

Susanne Dehmel, et al. J Neurosci. ;32(5):1660-1671.
5.
Figure 5

Figure 5. Suprathreshold discharge rates remain elevated after recovery from temporary threshold shift. From: Noise over-exposure alters long-term somatosensory-auditory processing in the dorsal cochlear nucleus – possible basis for tinnitus-related hyperactivity?.

Rate-level functions (RLFs) of noise exposed animals are steeper and show higher discharge rates across levels. Mean and standard error of rate level functions (10–85 dB, in 5 dB steps) are shown within 2 kHz bins of the characteristic frequency of the unit, included are RLFs recorded below/at/above the CF of the unit. White symbols: noise-exposed animals (n=11 animals / 463 RLFs, black symbols: control animals (n=9 animals / 252 RLFs).

Susanne Dehmel, et al. J Neurosci. ;32(5):1660-1671.
6.
Figure 2

Figure 2. Schematic of the bimodal stimulation paradigm. From: Noise over-exposure alters long-term somatosensory-auditory processing in the dorsal cochlear nucleus – possible basis for tinnitus-related hyperactivity?.

The immediate effect of bimodal stimulation was derived from a tone RLF and an immediately following bimodal RLF (in which the Sp5 stimulus preceded each tone stimulus). The long term effect of the bimodal stimulation is derived from the comparison between the first tone RLF and a second tone RLF recorded later in time after the bimodal RLF. For clarity the stimulus and response are shown only for one tone level of the RLF, which incorporated levels between 0 and 85 in 5 dB steps with 50 repetitions per level.

Susanne Dehmel, et al. J Neurosci. ;32(5):1660-1671.
7.
Figure 14

Figure 14. Chopper units show predominant long-term somatosensory enhancement in tinnitus and no-tinnitus animals. From: Noise over-exposure alters long-term somatosensory-auditory processing in the dorsal cochlear nucleus – possible basis for tinnitus-related hyperactivity?.

(A) Long term rate differences across level, Control: n=5 animals / 23 RLFs, no-tinnitus: n=2 animals / 15 RLFs, tinnitus: n=3 animals / 15 RLFs. All RLFs were recorded at the units‘ CF. (B) number of data points and the summed rate difference (C). Compared are control animals with noise-exposed animals that developed tinnitus or with noise-exposed animals that did not develop tinnitus. Suppression i.e., a reduction of discharge rate is shown as black plots or pies and enhancement i.e., increase of discharge rate as white plots or pies. For a detailed description see legend of .

Susanne Dehmel, et al. J Neurosci. ;32(5):1660-1671.
8.
Figure 9

Figure 9. Predominant temporal response types were buildup and chopper. From: Noise over-exposure alters long-term somatosensory-auditory processing in the dorsal cochlear nucleus – possible basis for tinnitus-related hyperactivity?.

PSTHs were determined from RLFs at the unit CF. Population (mean) PSTHs of the two main response types buildup (left) and chopper (right) are shown in the top panels. Levels between 10 dB and 90 dB are indicated with alternating black and white line plots. Lower panels show single level group PSTHs (mean and standard deviation) at 35 dB for buildup and 85 dB for chopper. The buildup response was most characteristic at lower levels and accompanied by onset components at higher levels (left panels). The precision of the chopping response increased with level (right panels).

Susanne Dehmel, et al. J Neurosci. ;32(5):1660-1671.
9.
Figure 10

Figure 10. Spontaneous rates are increased in buildup units of animals with tinnitus. From: Noise over-exposure alters long-term somatosensory-auditory processing in the dorsal cochlear nucleus – possible basis for tinnitus-related hyperactivity?.

Mean and standard error of SR of control animals (black), noise-exposed tinnitus animals (white) and no-tinnitus animals (gray) are plotted for the main response types. Stars indicate significant differences in ANOVA (p<0.05, adjustment for multiple comparisons: Sidak, details see text). Buildup control: n=5 animals / 12 units, buildup no-tinnitus: n=2 animals / 12 units, buildup tinnitus: n=2 animals / 7 units, chopper control: n=5 animals / 23 units, chopper no-tinnitus: n=2 animals / 17 units, chopper tinnitus: n=3 animals / 15 units, other control: n=6 animals / 16 units, other no-tinnitus: n=3 animals / 3 units, other tinnitus: n=3 animals / 8 units.

Susanne Dehmel, et al. J Neurosci. ;32(5):1660-1671.
10.
Figure 13

Figure 13. Long-term somatosensory (bimodal) effects in buildup units are predominated by enhancement in tinnitus animals. From: Noise over-exposure alters long-term somatosensory-auditory processing in the dorsal cochlear nucleus – possible basis for tinnitus-related hyperactivity?.

Rate differences between the first unimodal tone RLFs and a second tone RLFs repeated later in time, Control: n=5 animals / 11 RLFs, no-tinnitus: n=2 animals / 16 RLFs, tinnitus: n=1 animal / 2 RLFs. All RLFs were recorded at the units‘ CF. The pie charts show the number of data points (B) and the summed rate difference (C). Control animals are compared with noise-exposed animals that developed tinnitus or with noise-exposed animals that did not develop tinnitus. Suppression i.e., a reduction of discharge rate is shown as black plots or pies and enhancement i.e., increase of discharge rate as white plots or pies. For a detailed description see legend of .

Susanne Dehmel, et al. J Neurosci. ;32(5):1660-1671.
11.
Figure 8

Figure 8. Tinnitus is accompanied by a strengthening of bimodal enhancement. From: Noise over-exposure alters long-term somatosensory-auditory processing in the dorsal cochlear nucleus – possible basis for tinnitus-related hyperactivity?.

(A): Rate differences between (i) a RLFs during unimodal tone stimulation and a immediately following RLFs during bimodal tone & somatosensory stimulation ("immediate" change), control: n=8 animals / 50 RLFs, no-tinnitus: n=3 animals / 39 RLFs, tinnitus: n=4 animals / 30 RLFs and (ii) between the first unimodal tone RLFs and a second tone RLFs repeated later in time ("long-term"), control: n=8 animals / 49 RLFs, no-tinnitus: n=3 animals / 33 RLFs, tinnitus: 3 animals / 25 RLFs. All RLFs were recorded at the units‘ CF. The pie charts show the number of data points (B) and the summed immediate and long-term rate difference of the data (C). Compared are control animals with noise-exposed animals that developed tinnitus or with noise-exposed animals that did not develop tinnitus. Stars and arrows mark significant differences (linear mixed model statistics, adjustment for multiple comparisons: Sidak, p< 0.05; see material and methods, data analysis). For a detailed description see legend.

Susanne Dehmel, et al. J Neurosci. ;32(5):1660-1671.
12.
Figure 3

Figure 3. Narrowband noise exposure causes temporary threshold shift but permanently elevated spontaneous rates. From: Noise over-exposure alters long-term somatosensory-auditory processing in the dorsal cochlear nucleus – possible basis for tinnitus-related hyperactivity?.

The exposure-noise spectrum (gray area) is compared to the immediate threshold shift within an hour after the noise exposure (black symbols, mean and standard deviation 6 animals/10 ABRs of 1st and second noise exposures). Due to the considerable length of the noise exposure and ABR recordings, ABRs immediately after the noise exposure could not be recorded for all exposed animals. ABR threshold shift on the day of the DCN recordings (10 to 21 days after the second noise exposure) has recovered towards 0 dB (white circles: left exposed ear, white triangles: right ear; 11 animals), while SR were elevated (red graph; control: 9 animals / 135 units; noise-exposed: 12 animals / 296 units). Black stars indicate significant differences for ABR shifts (p<0.001, for details see text), red crosses indicate significance for SR differences (p<0.05, for details see text). Box around 8–18 kHz labels the tinnitus frequencies (). Red numbers at the x-axis are N for each bin of spontaneous rate differences given for control/noise exposed animals (“n/n”).

Susanne Dehmel, et al. J Neurosci. ;32(5):1660-1671.
13.
Figure 7

Figure 7. Effect of noise exposure on the balance between bimodal enhancement and suppression. From: Noise over-exposure alters long-term somatosensory-auditory processing in the dorsal cochlear nucleus – possible basis for tinnitus-related hyperactivity?.

(A): Left: Immediate rate differences between tone RLFs and immediately following bimodal RLFs (control: n=8 animals / 50 RLFs, noise-exposed: n=11 animals / 108 RLFs). All RLFs were recorded at the units‘ CF. Right: Long-term rate differences between the first tone RLF and a second tone RLF recorded later in time after bimodal stimulation (control: n=8 animals / 49 RLFs, noise-exposed: n=10 animals / 93 RLFs). The mean and standard-error are shown for suppression i.e., reduction of the discharge rate (black dots) and enhancement i.e., increase of discharge rate (white dots). The mean across level is given as a black or white number in the graph. Noise-exposed and control animals are shown in the upper and lower panels, respectively. Star and arrow marks significant difference (linear mixed model statistics, adjustment for multiple comparisons: Sidak, p< 0.05; for details see material and methods, data analysis). Data of (A) is collapsed across sound levels as pie charts in (B) and (C). (B): The number of datapoints with enhancement (white slices) or suppression (black slices) or no change (gray slices). (C): The sum of immediate and long-term rate differences (sum of rate difference from all units at all levels from 10 to 85dB) for noise-exposed and control animals. Colors as in B.

Susanne Dehmel, et al. J Neurosci. ;32(5):1660-1671.
14.
Figure 4

Figure 4. Narrow band noise exposure results in tinnitus in the 8–18 kHz band. From: Noise over-exposure alters long-term somatosensory-auditory processing in the dorsal cochlear nucleus – possible basis for tinnitus-related hyperactivity?.

Animals with noise exposure were divided into two groups: those with no significant gap detection in gap-carrier bands 8 to 18 kHz – “tinnitus group“, and those with significant gap detection at all carrier bands – “no-tinnitus group“. (A & B): Gap-PPI and (C & D): noise pulse-PPI. (A & C): The normalized startle (startle with the gap or noise pulse / startle without the gap or noise pulse) is shown for the two noise-exposure groups and the control group after the noise/sham exposure. The dotted line designates a normalized startle of 1, i.e., the startle amplitude without gap or noise pulse. (B & D): Dot plot of the absolute startle without the gap (black symbols) and with the gap (white symbols). The mean and 95 % confidence intervals are shown as dotted horizontal lines below and above the mean. The mean + 95 % confidence interval of the noise-floor is given for each group as a line plot (black: control, white: tinnitus, gray: no-tinnitus). Black bars, circles: sham exposure control group (n=4 animals), white bars, triangles: tinnitus group (n=4 animals), gray bars, squares: no-tinnitus group (n=3 animals). Normalized startle responses were derived from the mean of all trials over four days of one animal with the gap normalized to the mean of all trials of one animal without the gap. Stars mark significance in two-way repeated measures ANOVA (p<0.05, for details see text).

Susanne Dehmel, et al. J Neurosci. ;32(5):1660-1671.

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