1. cells in cochlear nucleus
The inferior colliculus is a nexus in the ascending auditory system and has a complexity comparable to VI in the visual system
The principal nuclei in the brainstem auditory pathway.
Each nucleus uniquely transforms an incoming spike train into an output that is different from the input
hair cell
auditory nerve fiber
cells in cochlear nucleus
descending cortico-collicular projections
to thalamus and then to cortex
excitatory
GABAergic
Inferior
Colliculus
glycinergic
dorsal
intermediate
ventral
nuclei of
the lateral lemniscus
Cochlear
nucleus
superior olivary complex
LSO
MSO
Cochlea
auditory
nerve
MNTB

2. cells in cochlear nucleus
The inferior colliculus is a nexus in the ascending auditory system has a complexity comparable to VI in the visual system
The principal nuclei in the brainstem auditory pathway.
Each nucleus uniquely transforms incoming an spike train into an output that is different from the input
hair cell
auditory nerve fiber
cells in cochlear nucleus
descending cortico-collicular projections
to thalamus and then to cortex
excitatory
GABAergic
Inferior
Colliculus
glycinergic
dorsal
intermediate
ventral
nuclei of
the lateral lemniscus
Cochlear
nucleus
MSO
superior olivary complex
LSO
Cochlea
auditory
nerve
MNTB

4. The Frequency Representation on the Cochlea is Preserved in Every Nucleus of the Central Auditory System, and thus the Auditory System is Tonotopically Organized
Inferior
colliculus
Medial geniculate
Superior olive
Cochlear nucleus
Auditory cortex
Cochlea
Auditory nerve
auditory cortex
medial geniculate
Inferior colliculus
cochlear nucleus
superior olive

5. Each cell type in the cochlear nucleus uniquely transforms
an incoming spike train into an output that is different from the input
to nucleus 1
to nucleus 2
to nucleus 3
to nucleus 4
to nucleus 5
Projections form the parallel pathways
in ascending auditory system
cells in cochlear nucleus

6. cells in cochlear nucleus
to nucleus 1
to nucleus 2
to nucleus 3
to nucleus 4
to nucleus 5
cells in cochlear nucleus
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

7. 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
LSO
MSO
MSO
Cochlea
auditory
nerve
MNTB
bushy cells

8. for localizing low frequencies for localizing high frequencies
Processing of interaural time disparities
for localizing low frequencies
Processing of interaural intensity disparities
for localizing high frequencies

9. interaural intensity differences (IIDs)
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)
Base
Right
Left

10. left ear louder
Base
Right
Left

11. Equally intense at both ears
Base
Right
Left

12. Right ear louder
Base
Right
Left

13. With low frequencies, sound waves just bend around the head and ears so there is no difference in sound intensity at the two ears
Base
Right
Left

14. With low frequencies, however, the sound arrives
at one ear earlier than it does at the other ear,
which creates interaural time differences (ITDs)
Base
Right
Left

15. Sound arrives at left ear first- left leads
Base
Right
Left

16. Arrives at both ears at the same time
Base
Right
Left

17. Sound arrives at right ear first- right leads
Base
Right
Left

18. Low frequencies are localized with interaural time disparities (ITDs)
High frequencies are localized with interaural intensity disparities (IIDs)

19. for localizing low frequencies for localizing high frequencies
Processing of interaural time disparities
for localizing low frequencies
Processing of interaural intensity disparities
for localizing high frequencies
ITD
IID
Spikes
10-20 microsec
Medial Superior Olive
MSO
Lateral Superior Olive
LSO
bushy cell
bushy cell

20. Formation of EI Property in LSO
DNLL
Inferior
Colliculus
Cochlear
nucleus
Cochlea
MNTB +
Interaural intensity disparity
IID
Excit ear louder
Inhib ear louder
Normalized Spike Count
1.0
0.5
monaural spike count
Formation of EI Property in LSO

21. Formation of EI Property in LSO
DNLL
Inferior
Colliculus
Cochlear
nucleus
Cochlea
MNTB +
LSO
IID
Excit ear louder
Inhib ear louder
Normalized Spike Count
1.0
0.5
monaural spike count X
Formation of EI Property in LSO

22. Formation of EI Property in LSO
DNLL
Inferior
Colliculus
Cochlear
nucleus
Cochlea
MNTB +
LSO
IID
Excit ear louder
Inhib ear louder
Normalized Spike Count
1.0
0.5
monaural spike count X
Formation of EI Property in LSO

23. Formation of EI Property in LSO
DNLL
Inferior
Colliculus
Cochlear
nucleus
Cochlea
MNTB +
LSO
IID
Excit ear louder
Inhib ear louder
Normalized Spike Count
1.0
0.5
monaural spike count X
Formation of EI Property in LSO

24. Formation of EI Property in LSO
DNLL
Inferior
Colliculus
Cochlear
nucleus
Cochlea
MNTB +
LSO
IID
Excit ear louder
Inhib ear louder
Normalized Spike Count
1.0
0.5
monaural spike count X
Formation of EI Property in LSO

25. Formation of EI Property in LSO
IID
Excit ear louder
Inhib ear louder
Normalized Spike Count
1.0
0.5
monaural spike count X
IID Function
Inferior
Colliculus X X
DNLL X X
Cochlear
nucleus +
LSO
Cochlea +
MNTB

26. + Normalized spike count Spikes Cochlear Nucleus LSO MNTB IID
louder in
excitatory ear
inhibitory ear
Spikes
LSO
MNTB +
Cochlear
Nucleus

27. all cells fire + Spikes Cochlear Nucleus LSO MNTB IID louder in
excitatory ear
inhibitory ear
all cells fire
Spikes

28. + Cochlear Nucleus LSO MNTB IID louder in excitatory ear
inhibitory ear

29. + Spikes Cochlear Nucleus LSO MNTB IID louder in excitatory ear
inhibitory ear
Spikes

30. + Spikes Cochlear Nucleus LSO MNTB IID louder in excitatory ear
inhibitory ear
Spikes

31. + Cochlear Nucleus LSO MNTB IID louder in excitatory ear
inhibitory ear

32. High frequencies- above about 3000 Hz
Low frequencies
High frequencies- above about 3000 Hz
Discharges are phase locked but not to every cycle
Discharges are not
phase locked
Discharges are phase locked to every cycle of the sinusoidal signal
Frequencies below 1000 Hz
Frequencies from Hz

33. Post-stimulus time(PST) histogram
tone burst
Raster display of phase-locked discharges evoked by 5 presentations of a tone burst
tone presentation
time (ms)
spike count
time (ms)
Post-stimulus time(PST) histogram

35. 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

36. Interaural time disparities have to be processed on
a frequency-by-frequency basis
left
ear
right
ear . .
constant phase difference between two ears
ITD
right
ear
left
ITD
right
ear
left
phase difference between two ears would continuously change

37. Medial nucleus of the trapezoid body
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.
MSO
LSO
Medial Superior Olive
Lateral Superior Olive
MNTB
Medial nucleus of the trapezoid body

38. Interaual time disparity (µsec)
MSO neurons are sensitive to Interaural time disparities of µs
Spikes
-40
+40
Interaual time disparity (µsec)
MSO
LSO
Medial Superior Olive
Lateral Superior Olive

39. Interaual time disparity (µsec)
MSO neurons are sensitive to Interaural time disparities of µs
Spikes
-40
+40
Interaual time disparity (µsec)
MSO
LSO
Medial Superior Olive
Lateral Superior Olive
MNTB
Medial nucleus of the trapezoid body

40. Interaual time disparity (µsec)
MSO neurons are sensitive to Interaural time disparities of µs
Spikes
-40
+40
Interaual time disparity (µsec)
MSO
LSO
Medial Superior Olive
Lateral Superior Olive
MNTB
Medial nucleus of the trapezoid body

41. Freq 1 Freq 2 Freq 3 Freq 4 Spikes Spikes ITD (µsec) Spikes ITD (µsec)
Freq 1
Spikes
ITD (µsec)
Spikes
Freq 2
ITD (µsec)
Spikes
Freq 3
Freq 4
ITD (µsec)
Spikes

42. Jeffress Model
MSO