1. Central Auditory Nervous System
CHAPTER 15
Central Auditory Nervous System

2. Central Nervous System Structures
Nucleus = a group of nerve cell bodies
Fiber Tract = a group of axons

4. Major Components of the Central Auditory Nervous System (CANS)
VIIIth cranial nerve
Cochlear Nucleus
Superior Olivary Complex
Lateral Lemniscus
Inferior Colliculus
Medial Geniculate Body
Primary Auditory Cortex
<Trapezoid Body>
Brainstem
Mid-brain
Thalamus
Temporal Lobe

5. Mid-Saggital View of Brain
4th Ventricle
Corpus Callosum
Cerebellum
Thalamus
Pons

9. MedGen Body
Inf Coll
Lat Lemn
SOC
Coch Nuc
VIIIth CN

10. Neural Web-Sites http://rprcsgi.rprc.washington.edu/
neuronames/hierarchy.html

11. Section Thru Brainstem Shows Cochlear Nucleus

12. The Superior Olivary Complex

13. Connections To the Superior Olivary Complex

14. Superior Olivary Processing Supports Localization
Lateral SO-- Interaural Intensity Differences
Medial SO-- Interaural Time Differences
(These are the two primary acoustic cues for localizing sounds)

15. Dorsal (back) Side of Brainstem
Thalamus
(medial geniculate)
Inferior Colliculus
4th Ventricle
Area of Pons

16. Inferior Colliculus

17. Thalamus in Purple

18. Auditory Radiations Connect
Medial Geniculate Body (in purple) to
Primary Auditory Cortex (in blue)

19. Lateral-Superior view of brain

20. Primary Auditory Cortex (AI): superior surface of the temporal lobe

21. 6 Cortical Layers Thalamic inputs >IV
project to pyramidal cells in layer III
Divergence from III
within AI
other cortical areas
contra AI
V and VI >>thalamus &IC
The auditory cortex, as most other neocortex, has been divided into six layers. Layer IV receives input from the thalamus. Layer I also receives input from MMGB. Cells in layer IV project to pyramidal cells in layer III. From layer III, auditory information diverges to several different locations including other layers of AI, contralateral AI (via corpus callosum), other primary auditory cortex layers I, II, IV and V. Layers V and VI project out of the auditory cortex.

22. Cortical Neurons Tonotopically and Spatiotopically organized
Highly Adaptable
Sensitive to CHANGES in Frequency and Intensity
Coding virtual pitch
demodulating complex signals (e.g. speech)
Tuning: Wide variability, some broad, some sharp w/ multi freq
Maps:
Tonotopic: Iso-frequency Columns.
Binaural/Monaural columns at right angles to tonotopic
columns. (Also referred to as binaural summation and suppression columns).
Callosal connex: in irregular bands.
Response Patterns:
Temporal: On//On-off//Off//Through
Level specificity: very non linear rate-intensity functions.
Responses to FM: either to direction or rate.
Responses to AM: tuning to specific rate.

23. Cortical Processing Pattern Recognition Duration Discrimination
Localization of Sounds
Selective Attention
Difficult to assign specific functional roles.
a) lesion studies provide some info
* lesions affect localization ability in
opposite hemifield.
* lesions affect performance in contralateral
ear in attention studies
i) but man may or may not equal animal performance
ii) and lesions in man are typically diffuse, not
isolated.
b) single cell responses show correlation to functions
i) responses to interaural time differences which show
up at SOC earliest, are preserved in auditory cortex.
ii) Primary Auditory cortex fiber responses show
preferential response to certain transient intervals, but do not show response to fundamental.
:: Q.E.D., pitch info not necessarily disrupted by lesions of primary auditory cortex

24. Cerebral Dominance/Laterality
Language Processing in the left hemisphere.
(Remember the right ear has the strongest connections to the left hemisphere)
Most people show a right-ear advantage in processing linguistic stimuli

25. Neurophysiological Measures
Gross Evoked Potentials-- Voltage changes in response to auditory stimulation recorded from the scalp
Single-Unit Measures-- Voltage (or other) changes recorded within a neuron

26. Auditory Evoked Potentials
Recorded in different time intervals (“epochs”) following a sound
Earlier epochs come from lower in the system
Later epochs come from higher in the system

27. Examples of AEP Epochs Electrocochleography-- within 5 milliseconds
Auditory Brainstem Response-- thru 10 ms
Middle Latency Response-- thru 75 ms
Auditory Late Response-- thru 200 ms

28. Auditory Brainstem ResponseIV V
III II I
Amplitude (V)
Amp V
Wave V Latency
Time (ms) 10

29. GENERATORS of ABR WAVESI II
III IV V
Distal VIIIth nerve
Medial VIIIth nerve
Cochlear Nucleus
Superior Olivary Complex
Lateral Lemniscus & Inferior Colliculus

30. The Acoustic Reflex Afferent: Efferent: VIIIth nerve Cochlear Nucleus
Superior Olivary Complex
Efferent:
VIIth nerve nucleus
VIIth nerve
Stapedius muscle