Download Processing in The Superior Olivary Complex

Processing in The Superior Olivary Complex
Alan R. Palmer
Medical Research Council Institute of Hearing Research
University Park
Nottingham NG7 2RD, UK
Binaural cues for Localising Sounds in Space
time
Interaural Time Differences (ITDs)
Interaural Level Differences (ILDs)
Binaural Mechanisms of Sound
Localization
• Interaural time (or phase) difference at low frequency are initially
analysed in the MSO by coincidence detectors connected by a
delay line system.
• Interaural level differences at high frequency are initially
analysed in the LSO by input that is inhibitory from one
ear and excitatory from the other.
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The Auditory Nervous System
Cortex
Cortex
MGB
Excitatory
IC
GABAergic
Glycinergic
Interaural Level Differences
DNLL
PVCN
Cochlea
Inferior Colliculus
Nuclei of the Lateral Lemniscus
Lateral
Lemniscus
Interaural
Time Differences
Cochlear Nucleus
DCN
AVCN
Medial Geniculate Body
MSO
MNTB
Lateral Superior Olive
Medial Superior Olive
Medial Nucleus of the Trapezoid Body
Superior Olive
Binaural Hearing
The ability to extract specific forms of auditory
information using two ears
ears, that would not be
possible using one ear only.
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Advantages of Two Ears
• Improved detection / increased loudness
• Removing interference from echoes
• Improved detection of sounds in
interfering backgrounds
• Spatial localization
• Detection of auditory motion
20 dB
700 μs
Nordlund
Interaural level differences
((high
g frequency)
q
y)
3
PARALLEL PROCESSING OF INFORMATION IN THE COCHLEAR NUCLEUS
To inferior colliculus: information about pinna
sound transformations
To medial superior olive: information about sound
localisation using timing (and possibly time coding of speech)
To lateral superior olive: information about
sound localisation using interaural intensity
Either commisural or to inferior colliculus
information about sound level and voice pitch
To medial nucleus of the trapezoid body: information
about sound localisation using interaural intensity
To inferior colliculus: information about complex sounds
(possibly place coding of speech)
Input from cochlear nerve
Interaural Level Difference Pathway
Excitatory
Inhibitory
+
+
_
+
+
4
Ipsilateral
Contralateral
100
Sound lev
vel (dB SPL)
100
20
0.125
20
32
0.125
Frequency (kHz)
32
Caird and Klinke 1983
5
Caspary and Finlayson (1991)
Irvine (1986)
Interaural time differences
((low frequency)
q
y)
The discharges of cochlear nerve fibres to lowlowfrequency sounds are not random;
they occur at particular times (phase
(phase locking).
locking).
Evans (1975)
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PARALLEL PROCESSING OF INFORMATION IN THE COCHLEAR NUCLEUS
To medial superior olive: information about sound
localisation using timing (and possibly time coding of speech)
To inferior colliculus: information about pinna
sound transformations
To lateral superior olive: information about
sound localisation using interaural intensity
To medial nucleus of the trapezoid body: information
about sound localisation using interaural intensity
Either commisural or to inferior colliculus
information about sound level and voice pitch
To inferior colliculus: information about complex sounds
(possibly place coding of speech)
Input from cochlear nerve
Interaural Time Difference Pathway
Response
The coincidence detection model of Jeffress (1948) is the
widely accepted model for lowlow-frequency sound
localisation
0
Interaural Time Difference
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Response
0
Interaural Time Difference
ALT TAB
Department of Neurophysiology,University of Wisconsin
Ipsilateral
Contralateral
Barn Owl: Konishi et al 1988
8
Pena et al 2001
Matches between the inputs from the two ears
in the Barn Owl Nucleus Laminaris
Fischer and Pena 2009
Pathways for analysing interaural time differences
Excitatory
To inferior colliculus
Left Ear
+
Semicircular
Canals
Cochlear
Nucleus
Cochlear
Nucleus
+
+
Right Ear
+
Window
MSO
Large calyx synaptic ending
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0 μs Time Delay
0 μs
Cochlear
Nucleus
Left Ear
Cochlear
Nucleus
Right Ear
Semicir cular
Can als
Window
MSO
Auditory Nerve Activity
Large calyx synaptic ending
0 μs Time Delay
Arrives at left ear 300 μs
later than at the right
300 μs
Cochlear
Nucleus
Left Ear
Cochlear
Nucleus
Right Ear
Se mi cir cul ar
Canals
Window
MSO
Auditory Nerve Activity
Large calyx synaptic ending
300 μs Time Delay
Coincident spikes
Arrives at left ear 300 μs
later than at the right
0 μs Time Delay
300 μs
0 μs
Cochlear
Nucleus
Left Ear
Cochlear
Nucleus
Right Ear
Se mi cir cul ar
Canals
Window
MSO
Auditory Nerve Activity
Large calyx synaptic ending
300 μs Time Delay
0 μs Time Delay
Coincident spikes
10
-600
-300
0
ITD (μs)
300
600
Interaural Phase Sensitivity in the MSO
Best Delay
1 ms
1 ms
Yin and Chan (1988)
Smith et al 1993
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Bekius et al 1999
Noise
BF tones
Guinea Pig
Palmer et al., 1990
Cat
Yin et al., 1986
Palmer et al 1990
Distribution of peaks of ITD functions in response to
interaurally-delayed noise
Physiological range
Number of Neurrones
80
60
40
20
0
-500
0
500
1000
Interaural Delays (μs)
McAlpine Jiang and Palmer 2001
12
McAlpine, Jiang and Palmer 1996
1/8
1/4
1/2 cycle
1/16
McAlpine Jiang and Palmer 2001
Brand et al 2002
13
Grothe 2003
Brand et al., 2002
325 Hz
Normalised Response
500 Hz
700 Hz
-1000
-500
0
500
1000
ITD (μs)
1.0 kHz
1.4 kHz
-1000
-500
0
ITD (μs)
500
1000
-1000
-500
0
500
1000
McAlpine Jiang and Palmer 2001
ITD (μs)
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Distribution of steepest slopes of ITD functions in response to
interaurally-delayed noise
Physiological range
Number of Neurones
80
60
40
20
0
-500
0
500
1000
Interaural Delays (μs)
McAlpine Jiang and Palmer 2001
0.5
Interaaural Time Difference (μs)
Normalised Response
0.8
0.6
0.4
0.2
0.0
-1000
-500
0
500
1000
Interaural Time Difference (μs)
Interaural Phase Difference (cycles)
600
1.0
500
0.4
400
0.3
300
0.2
200
0.1
100
0
0.0
0.00 0.25 0.50 0.75 1.00 1.25 1.50
Frequency (kHz)
McAlpine Jiang and Palmer 2001
ITD processing is BFBF-dependent.
ITD functions are steepest around midline.
The consequence of this is that:
As ITD increases across the physiological range the activity at
any frequency increases
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Descending pathways
Spangler and Warr 1991
Warr 1978, Warr and Guinan 1979
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Spoendlin 1971
Wiederhold and Kiang 1971
Function of the descending or centrifugal
innervation
•
Protection from acoustic trauma
• Control of the mechanical state of the cochlea
• Involvement in selective attention
• Detection of complex signal in noise
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