Transcript 0 - HomePage Server for UT Psychology

The Frequency Representation on the Cochlea is Preserved in Every Nucleus
of the Central Auditory System, and thus the Auditory System is Tonotopically
Organized
auditory cortex
Auditory
cortex
medial geniculate
Inferior colliculus
cochlear nucleus
Auditory
nerve
Cochlear
nucleus
Medial
geniculate
Medial
geniculate
Inferior
colliculus
medial geniculate
Inferior
colliculus
superior olive
Superior
olive
Superior
olive
Inferior colliculus
Cochlear
nucleus
cochlear nucleus
Auditory
nerve
Each cell type in the cochlear nucleus uniquely transforms
an incoming spike train into an output that is different from the input
cells in cochlear nucleus
Projections form the parallel pathways
in ascending auditory system
to nucleus 1
to nucleus 2
to nucleus 3
to nucleus 4
to nucleus 5
cells in cochlear nucleus
to nucleus 1
to nucleus 2
to nucleus 3
to nucleus 4
to nucleus 5
Projections from each cell group in
the cochlear nucleus are
tontopically organized
to nucleus 1
to nucleus 2
to nucleus 3
to nucleus 4
to nucleus 5
Lateral Superior Olive (LSO) and Medial Superior Olive (MSO)
are both binaural nuclei that process the cues
for sound localization
excitatory
GABAergic
Inferior
Colliculus
glycinergic
dorsal
intermediate
ventral
Cochlear
nucleus
superior olivary complex
LSO
MSO
Cochlea
auditory
nerve
bushy cells
MNTB
Processing of interaural time disparities
for localizing low frequencies
Processing of interaural intensity disparities
for localizing high frequencies
With high frequencies, the ears and head block some
of the sound, making the sound louder in one ear
than the other, which creates
interaural intensity differences (IIDs)
Right
Base
Left
Base
left ear louder
Right
Base
Left
Base
Equally intense at both ears
Right
Base
Left
Base
Right ear louder
Right
Base
Left
Base
With low frequencies, sound waves just bend around
the head and ears so there is no difference in sound
intensity at the two ears
Right
Base
Left
Base
With low frequencies, however, the sound arrives
at one ear earlier than it does at the other ear,
which creates interaural time differences (ITDs)
Right
Base
Left
Base
Sound arrives at left ear first- left leads
Right
Base
Left
Base
Arrives at both ears at the same time
Right
Base
Left
Base
Sound arrives at right ear first- right leads
Right
Base
Left
Base
Medial Superior Olive
MSO
Processing of interaural time disparities
for localizing low frequencies
bushy cell
Spikes
10-20 microsec
ITD
Lateral Superior Olive
LSO
Processing of interaural intensity disparities
for localizing high frequencies
Spikes
bushy cell
IID
Formation of EI Property in LSO
monaural spike count
Normalized Spike
Count
1.0
Inferior
Colliculus
0.5
DNLL
0
Excit ear louder 0 Inhib ear louder
Interaural intensity disparity
IID
Cochlear
nucleus
+ LSO
Cochlea
MNTB
Formation of EI Property in LSO
monaural spike count
Normalized Spike
Count
1.0
X
Inferior
Colliculus
0.5
DNLL
0
Excit ear louder 0 Inhib ear louder
IID
Cochlear
nucleus
Cochlea
+ LSO
+
MNTB
Formation of EI Property in LSO
monaural spike count
Normalized Spike
Count
1.0
0.5
X
Inferior
Colliculus
X
DNLL
0
Excit ear louder 0 Inhib ear louder
IID
Cochlear
nucleus
Cochlea
+ LSO
+
MNTB
Formation of EI Property in LSO
monaural spike count
Normalized Spike
Count
1.0
0.5
X
Inferior
Colliculus
X
DNLL
X
0
Excit ear louder 0 Inhib ear louder
IID
Cochlear
nucleus
Cochlea
+ LSO
+
MNTB
Formation of EI Property in LSO
monaural spike count
Normalized Spike
Count
1.0
0.5
X
Inferior
Colliculus
X
DNLL
X
0
X
Excit ear louder 0 Inhib ear louder
IID
Cochlear
nucleus
Cochlea
+ LSO
+
MNTB
Formation of EI Property in LSO
monaural spike count
IID
Function
Normalized Spike
Count
1.0
0.5
X
Inferior
Colliculus
X
DNLL
X
0
X
X
Excit ear louder 0 Inhib ear louder
IID
Cochlear
nucleus
Cochlea
+ LSO
+
MNTB
Spikes
Spikes
Spikes
Normalized spike count
Spikes
louder in
excitatory ear
+
0
IID
louder in
inhibitory ear
Cochlear
Nucleus
LSO
+
MNTB
Spikes
Spikes
Spikes
Spikes
all cells fire
louder in
excitatory ear
+
0
IID
louder in
inhibitory ear
Cochlear
Nucleus
LSO
+
MNTB
louder in
excitatory ear
+
0
IID
louder in
inhibitory ear
Cochlear
Nucleus
LSO
+
MNTB
Spikes
Spikes
Spikes
Spikes
louder in
excitatory ear
+
0
IID
louder in
inhibitory ear
Cochlear
Nucleus
LSO
+
MNTB
Spikes
Spikes
Spikes
Spikes
louder in
excitatory ear
+
0
IID
louder in
inhibitory ear
Cochlear
Nucleus
LSO
+
MNTB
louder in
excitatory ear
+
0
IID
louder in
inhibitory ear
Cochlear
Nucleus
LSO
+
MNTB
Low frequencies
Frequencies below 1000 Hz
Discharges are phase locked to
every cycle of the sinusoidal
signal
Frequencies from 1000-3000 Hz
Discharges are phase locked but
not to every cycle
High frequencies- above about 3000 Hz
Discharges are not
phase locked
tone burst
Raster display of phase-locked
discharges evoked by 5
presentations of a tone burst
time (ms)
Post-stimulus time(PST) histogram
time (ms)
right ear
phase-locked discharges
left ear
spikes at right ear
ITD
spikes at left ear
Due to phase-locking, the timing of spikes in the auditory
nerve fibers from the two ears accurately represents, and
thereby preserves, the ITD in the auditory pathway
Interaural time disparities have to be processed on
a frequency-by-frequency basis
right
ear
left
ear
. .
constant phase difference between two ears
right
ear
left
ear
ITD
phase difference between two ears would continuously change
right
ear
left
ear
ITD
In 1948 Lloyd Jeffress, a professor in the Psychology
Department at The University of Texas at Austin, proposed a
model could explain how low frequency sounds are localized.
The model includes:
1) structural features, i.e., delay lines resulting from differences in axonal lenghts;
2) The neuronal process of coincidence detection. Specifically, the requirement that
action potentials arrive at a target neuron simultaneously to activate the binaural
neuron.
3) Topographically organized selective features that allows sound location to be
repesented as a place of maximal activity.
4) How all of those features are activated by interaural time disparities, the cues
animals use to localize low frequency sounds.
Medial Superior Olive
MSO
Spikes
MSO neurons are sensitive to Interaural time disparities
of 10-20 µs
-40 0
+40
Interaual time disparity (µsec)
Medial Superior Olive
MSO
Spikes
MSO neurons are sensitive to Interaural time disparities
of 10-20 µs
-40 0
+40
Interaual time disparity (µsec)
Medial Superior Olive
MSO
Spikes
MSO neurons are sensitive to Interaural time disparities
of 10-20 µs
-40 0
+40
Interaual time disparity (µsec)
Medial Superior Olive
MSO
Spikes
Freq 1
0
Freq 2
Spikes
ITD (µsec)
0
Freq 3
Spikes
ITD (µsec)
0
ITD (µsec)
Spikes
Freq 4
0
ITD (µsec)
Jeffress Model
MSO