Transcript Slide 1

DISTORTION PRODUCT OTOACOUSTIC EMISSIONS PROVIDE CLUES TO HEARING MECHANISMS IN THE FROG
Pantelis N. Vassilakis, Sebastiaan W. F. Meenderink, and Peter M. Narins
Department of Physiological Science University of California at Los Angeles - Los Angeles, CA 90095-1606 USA (Corresponding author: Peter M. Narins: [email protected])
RESULTS
INTRODUCTION - BACKGROUND
Experiment 1: DPOAE I/O curves
f = 600Hz (R. catesbeiana)
f1 == 1500Hz
f1
1500Hz (R.
(R. catesbeiana)
catesbeiana)
35
Noise
Noise
25
25
AP: 2f1-f2
15
BP: 2f1-f2
15
5
Noise
0
-5
-10
1250
1250
750
1750
2250
f 1 (Hz)
50
60
70
80
90
40
b
50
Amphibian Papilla
70
80
90
Basilar Papilla
45
f1 =
= 1800Hz
(R. pipiens)
p. pipiens)
f1
1800Hz (R.
f1 =
(R. p.
pipiens)
f1
= 800Hz
800Hz (R.
pipiens)
f1 =
(R. catesbeiana)
f1
= 600Hz
600Hz (R.
catesbeiana)
35
f1 =
= 1500Hz
(R. catesbeiana)
catesbeiana)
f1
1500Hz (R.
35
-10
Amphibian
papilla
Basilar
papilla
750
1250
1750
2250
2750
f 2 (Hz)
50
c
60
70
80
90
30
40
d
L1 = L2 (dB SPL)
50
60
70
80
90
L1 = L2 (dB SPL)
5
2f2-f1
Noise
0
-5
-10
L2 = 60dB SPL
FIG. 2
10
f1=800Hz (AP)
f1=1500Hz (BP)
f1=1500Hz (BP)
Noise
Noise
5
0
-5
5
0
-5
-10
-10
-15
-15
50
55
60
65
45
50
b
L2 (dB SPL)
10
f1=800Hz (AP)
f1=1500Hz (BP)
Noise
Noise
5
0
-5
-15
50
55
60
0
-5
-10
65
45
L2 (dB SPL)
50
2250
2750
55
60
65
The level of
each DPOAE
depends most
on the level of
its neighboring
(in frequency)
primary
[i.e. (b) & (c)].
L1-L2 = 10dB
= 7.5dB
1100
1600
2100
2600
f 2 (Hz)
2f2-f1
5
Noise
0
-5
-10
600
1100
1100
1600
2100
2600
DP frequency (Hz)
Male
Male
Female
Female
Noise
Noise
5
0
-5
-10
5
0
-5
-10
FIG. 6
750
1250
1750
2250
-15
2750
DP Frequency (Hz)
a
250
750
1250
1750
2250
2750
f 2 (Hz)
b
= 0dB
= -2.5dB
= -5dB
0
= -7.5dB
Male
Male
10
10
Female
= -10dB
Female
Noise
Noise
-15
200
400
600
800
1000
1200
f 1 (Hz)
a
1400
1600
FIG. 3
10
2f 2-f 1 Level (dB SPL)
-10
2f 1-f 2 Level (dB SPL)
Noise
-5
5
0
-5
-10
FIG. 7
= 7.5dB
-15
= 5dB
100
= 2.5dB
5
5
0
-5
-10
L1-L2 = 10dB
600
1100
1600
2100
2600
-15
100
600
1100
1600
2100
2600
= 0dB
= -2.5dB
a
DP Frequency (Hz)
b
f 2 (Hz)
= -5dB
0
= -7.5dB
= -10dB
Noise
-5
-10
-15
200
400
600
800
1000
f 1 (Hz)
1200
1400
1600
1 _ 2f1-f2 I/O curves from the frog AP are similar to
mammalian DPOAE I/O curves (non-monotonic
response with a notch for L1,L2~ 70dB SPL), indicating
that an amplification process may be present in the frog
AP. Since the frog ear lacks OHCs, our results
implicate hair cell bundle movement, which may be
analogous to mammalian OHC somatic motility. BP
DPOAE I/O curves are rather monotonic, suggesting
that no amplification process is present in this papilla.
The difference between AP and BP may be linked to
respective innervation differences, consistent with the
fact that only the AP is tonotopically organized.(Fig. 1)
2 _ Highest DPOAEs (R. p. pipiens, f2/f1 = 1.15) were
generally obtained for L1 L2. Our data are again
similar to mammalian results, consistent with a
similarity in neural tuning curves. Since the frog ear
lacks a BM (thought to be responsible for the shape of
mammalian neural tuning curves), the observed
similarity between frogs and mammals suggests that
some other mechanical structure (possibly the tectorial
membrane) may function analogously to the
mammalian BM. (Figs. 2,3)
3 _ DPOAEs are produced in both papillae. R.
catesbeiana generally produce higher amplitude
emissions than R. p. pipiens. (Figs. 4,5)
4 _ In contrast to mammalian results, generation of the
2f1-f2 DPOAE in the frog appears to occur primarily at
or near the DPOAE frequency place, while the
generation of the 2f2-f1 DPOAE occurs primarily at a
frequency place between the primaries. This difference
may be linked to an anatomical difference that results
in the acoustic energy following opposite paths through
the mammalian and frog inner ears. (Figs 4,5)
5 _ Females from both R. p. pipiens and R. catesbeiana
produce higher level emissions than males in both
papillae. DPOAE-based sexual dimorphism has been
reported in humans and other mammals. It may be
linked to inner ear anatomical differences, middle ear
transfer impedance differences, hormonal differences,
nerve-fiber tuning differences, and/or behavioral and
environmental factors. (Figs, 6,7)
REFERENCES
R. catesbeiana
= 2.5dB
5
2f 1-f2 Level (dB SPL)
600
Basilar
papilla
10
10
= 5dB
2f 2-f1 Level (dB SPL)
Amphibian
papilla
DPOAEs levels from R. p. pipiens (Fig. 4) and R. catesbeiana (Fig. 5) as a function
of: (a) f1, (b) f2, and (c) DP frequency. The dashed vertical line marks the “break” in
the frequency coverage of the AP and the BP. DPOAEs arise from both papillae. For
2f1-f2, the dip in the plot aligns best with the vertical line when DPOAE level is
plotted as a function of DP frequency (c). For 2f2-f1, the alignment is best when
DPOAE level is plotted as a function of f2 (b). Note- there is also near alignment in
the plot of DPOAE level against f1 (a).
250
10
b
-10
c
-15
Results from Fig.
2 in the form of
DPOAE
audiograms,
confirming
maximum
DPOAE levels
for |L1-L2|  0 at
most frequencies
tested and for
both cubic
DPOAEs.
-5
100
DP frequency (Hz)
L1 (dB SPL)
d
0
R. p. pipiens
-15
45
Noise
65
f1=800Hz (AP)
f1=1500Hz (BP)
2f2 -f1 Level (dB SPL)
2f 2-f 1 Level (dB SPL)
60
L2 = 60dB SPL
-10
c
55
1750
L1 (dB SPL)
L1 = 60dB SPL
10
DPOAE levels
versus L2 for
fixed L1 [(a) &
(c)] and versus
L1 for fixed L2
[(b) & (d)].
1250
2f 2-f 1 Level (dB SPL)
f1=800Hz (AP)
750
c
2f 1-f 2 Level (dB SPL)
10
FIG. 5
-15
250
L1 = 60dB SPL
2f2-f1
2f1-f2
-15
Experiment 2: DPOAE vs. |L1-L2| (R. p. pipiens)
2600
10
DP Level (dB SPL)
40
DP Level (dB SPL)
-15
30
2100
2f1-f2
-5
-15
1600
5
b
5
-5
1100
1100
f 1 (Hz)
100
10
5
600
-15
b
15
Noise
-5
250
BP: 2f2-f1
2f2-f1
FIG. 4
-15
AP: 2f2-f1
15
-10
2f1-f2
0
25
25
-5
10
5
Noise
Noise
2f 2-f 1 Level (dB SPL)
60
L1 = L2 (dB SPL)
45
0
2f1-f2
30
L1 = L2 (dB SPL)
Noise
a
DP Level (dB SPL)
40
2f2-f1
5
100
2750
-15
30
2f1-f2
-15
a
DP Level (dB SPL)
-15
5
Data recording / analysis: Signal from
subjects’ ears was fed to an FFT analyzer
(SRS-SR770). The DPOAE level reported
was the max. of 5 adjacent analysis bands
centered at the DPOAE frequency band.
Noise was estimated by averaging the
levels of 18 analysis bands surrounding
the 5 bands used to determine the DPOAE
level (system distortion: ~ 84dB below the
primaries).
2f2-f1
-15
-5
R. catesbeiana
2f1-f2
10
METHODS
Stimuli: Primary-tone parameters: 240 ≤
f2, f1 ≤ 3000Hz (~ 0.1f1Hz steps) and 35 ≤
L1, L2 ≤ 85dB (2.5dB steps). Stimuli
generated by a Real Time Processor (TDTRP2) and fed to a speaker/microphone
assembly (ER10-C).
R. p. pipiens
250
-5
10
5
5
a
Anesthesia: Intramuscular injection,
pentobarbital sodium solution (Nembutal,
50mg/ml: ~0.9-1.0 μl/g body mass)
DP Level (dB SPL)
f1 == 1800Hz
pipiens)
f1
1800Hz (R. p.
pipiens)
f11 = 600Hz (R. catesbeiana)
35
45
Subjects: 10 northern leopard frogs (R. p.
pipiens) and 10 bullfrogs (R. catesbeiana),
5 males and 5 females each - both ears.
10
45
2f 1-f 2 Level (dB SPL)
The present work examines the DPOAE
parameter space in the frog (in terms of
the primary tones’ frequency range as well
as absolute and relative SP levels) and the
relationship among DPOAE levels and the
subjects’ species and sex (f2/f1 = 1.15)
Basilar Papilla
f1 == 800Hz
pipiens)
f1
800Hz (R.
(R. p.
pipiens)
2f 1-f 2 Level (dB SPL)
DPOAEs have been recorded from the
frog (Van Dijk et al, 2002), despite the
fact that the frog inner ear has neither a
BM (Capranica, 1976) nor
morphologically distinct OHCs (Lewis et
al., 1982).
Experiment 3: DPOAE Audiograms (L1, L2 = 60dB SPL)
DP Level (dB SPL)
45
a
Mammalian DPOAEs have been linked to
the inner ear’s (a) outer hair cell (OHC)
motility, (b) cochlear amplifier, and (c)
overlap of the primary tones’ basilar
membrane (BM) disturbances.
FIG. 1
Amphibian Papilla
2f 1-f 2 Level (dB SPL)
Distortion product otoacoustic emissions
(DPOAEs) arise when the ear is
stimulated by two sine signals (primaries)
with appropriate frequency (f1, f2) and
stimulus (L1, L2) levels. Otoacoustic
emissions (OAEs) in general and
DPOAEs in particular have provided
means of examining inner ear mechanisms
in mammals (Shera & Guinan, 2003) and
other vertebrates (Rosowski et al., 1984).
CONCLUSIONS
Comparison between DPOAE audiograms from both ears of 5 male and 5 female R.
p. pipiens (Fig. 6) and R. catesbeiana (Fig. 7).
(a) The level of 2f1-f2 is plotted as a function of DP frequency and (b) the level of
2f2-f1 is plotted as a function of f2 (see Figs. 4,5). Female subjects consistently
exhibit stronger emissions than males, especially from the BP.
Capranica, R. R. (1976). “Morphology and physiology of the
auditory system,” in Frog Neurobiology, edited by R. Llinas, and
W. Precht (Springer Verlag, Berlin), pp. 551-575.
Lewis, E. R., Leverenz, E. L., and Koyama, H. (1982). “The
tonotopic organization of the bullfrog amphibian papilla, an
auditory organ lacking a basilar membrane,” J. Comp. Physiol.,
145: 437-445.
Rosowski, J. J., Peake, W. T., and White, J. R. (1984). “Cochlear
nonlinearities inferred from two-tone distortion products in the
ear canal of the alligator lizard,” Hear. Res., 13: 141-158.
Shera, C. A., and Guinan, J. J. Jr. (2003). “Stimulus-frequencyemission group delay: A test of coherent reflection filtering and a
window on cochlear tuning,” J. Acoust. Soc. Am., 113(5): 27622772.
Van Dijk, P., Mason, M. J., and Narins, P. M. (2002). “Distortion
product otoacoustic emissions in frogs: correlation with middle
and inner ear properties,” Hear. Res., 173: 100-108.