Download The Auditory Nervous System

The Auditory Nervous System
Processing in The Superior Olivary Complex
Cortex
Cortex
MGB
Alan R. Palmer
Medical Research Council Institute of Hearing Research
University Park
Nottingham NG7 2RD, UK
Excitatory
IC
GABAergic
Glycinergic
Interaural Level Differences
DNLL
PVCN
Cochlea
AVCN
Inferior Colliculus
Nuclei of the Lateral Lemniscus
Lateral
Lemniscus
Interaural
Time Differences
Cochlear Nucleus
DCN
MSO
MNTB
Advantages of Two Ears
Medial Geniculate Body
• Improved detection / increased loudness
• Removing interference from echoes
• Improved detection of sounds in
interfering backgrounds
• Spatial localization
• Detection of auditory motion
Lateral Superior Olive
Medial Superior Olive
Medial Nucleus of the Trapezoid Body
Superior Olive
Binaural cues for Localising Sounds in Space
20 dB
time
700 μs
Interaural Time Differences (ITDs)
Interaural Level Differences (ILDs)
Nordlund
Binaural Mechanisms of Sound
Localization
• Interaural time (or phase) difference at low frequency are initially
Binaural Hearing
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.
The ability to extract specific forms of auditory
information using two ears,
ears that would not be
possible using one ear only.
Interaural level differences
((high
g frequency)
q
y)
1
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
Caspary and Finlayson (1991)
Excitatory
Inhibitory
+
_
+
Interaural time differences
((low frequency)
q
y)
+
Ipsilateral
Contralateral
100
The discharges of cochlear nerve fibres to lowlowfrequency sounds are not random;
they occur at particular times (phase
(phase locking).
locking).
100
Sound levvel (dB SPL)
+
Irvine (1986)
20
0.125
20
32
0.125
32
Frequency (kHz)
Caird and Klinke 1983
Evans (1975)
2
Response
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
0
Interaural Time Difference
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
Pena et al 2001
The coincidence detection model of Jeffress (1948) is the
widely accepted model for lowlow-frequency sound
localisation
Matches between the inputs from the two ears
in the Barn Owl Nucleus Laminaris
ALT TAB
Department of Neurophysiology,University of Wisconsin
Fischer and Pena 2009
Response
Pathways for analysing interaural time differences
Ipsilateral
Excitatory
To inferior colliculus
0
Interaural Time Difference
Left Ear
+
Semicircular
Canals
Cochlear
Nucleus
Cochlear
Nucleus
+
+
Right Ear
+
Window
MSO
Contralateral
Large calyx synaptic ending
Barn Owl: Konishi et al 1988
3
0 μs Time Delay
0 μs
-600
Cochlear
Nucleus
Left Ear
Cochlear
Nucleus
-300
0
ITD (μs)
300
600
Right Ear
Se micir cul ar
Can als
W in d ow
MSO
Auditory Nerve Activity
Large calyx synaptic ending
0 μs Time Delay
Bekius et al 1999
Interaural Phase Sensitivity in the MSO
Arrives at left ear 300 μs
later than at the right
Best Delay
Noise
BF tones
300 μs
Cochlear
Nucleus
Left Ear
Cochlear
Nucleus
Right Ear
Se micircular
Can als
1 ms
1 ms
Guinea Pig
Palmer et al., 1990
Win dow
MSO
Cat
Yin et al., 1986
Auditory Nerve Activity
Large calyx synaptic ending
300 μs Time Delay
Coincident spikes
Yin and Chan (1988)
Arrives at left ear 300 μs
later than at the right
0 μs Time Delay
Palmer et al 1990
Smith et al 1993
Distribution of peaks of ITD functions in response to
interaurally-delayed noise
300 μs
0 μs
Physiological range
Left Ear
Cochlear
Nucleus
80
Right Ear
Se micircula r
Can als
Win dow
MSO
Auditory Nerve Activity
Number of Neurrones
Cochlear
Nucleus
60
40
20
Large calyx synaptic ending
300 μs Time Delay
0 μs Time Delay
0
-500
0
500
1000
Interaural Delays (μs)
Coincident spikes
McAlpine Jiang and Palmer 2001
4
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)
Grothe 2003
McAlpine, Jiang and Palmer 1996
1/8
1/4
McAlpine Jiang and Palmer 2001
1/2 cycle
0.5
Interaaural Time Difference (μs)
Noormalised Response
1/16
0.8
0.6
0.4
0.2
0.0
-1000
-500
0
500
1000
Interaural Time Difference (μs)
McAlpine Jiang and Palmer 2001
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
Brand et al., 2002
325 Hz
ITD processing is BFBF-dependent.
500 Hz
Normalised Response
ITD functions are steepest around midline.
700 Hz
-1000
-500
0
500
The consequence of this is that:
1000
ITD (μs)
1.0 kHz
As ITD increases across the physiological range the activity at
any frequency increases
1.4 kHz
Brand et al 2002
-1000
-500
0
ITD (μs)
500
1000
-1000
-500
0
500
1000
McAlpine Jiang and Palmer 2001
ITD (μs)
5
Descending pathways
Spoendlin 1971
Spangler and Warr 1991
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
Warr 1978, Warr and Guinan 1979
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