Cell Types and Physiology in the
CANS
Major Components of the Central
Auditory Nervous System (CANS)
•
•
•
•
•
•
•
VIIIth cranial nerve
Cochlear Nucleus
Trapezoid body
Superior Olivary Complex
Lateral Lemniscus
Inferior Colliculus
Medial Geniculate Body
Primary Auditory Cortex
Brainstem
Mid-brain
Thalamus
Temporal Lobe
•
•
•
•
•
•
MedGen Body
Inf Coll
Lat Lemn
SOC
Coch Nuc
VIIIth CN
VIIIth Nerve Afferents
Time (ms)
40
36
32
28
24
20
Sound Off
16
12
8
Sound On
4
35
30
25
20
15
10
5
0
0
– AVCN
– PVCN
– DCN
AP Rate
• Bipolar Neurons
• Primary Response Type
50
45
• Synapse in:
40
Section Thru Brainstem Shows
Cochlear Nucleus
Cochlear Nucleus
•
•
•
•
Wide variety of cell types
AVCN >>to ipsi and contra SOC
PVCN >>to contra Lat. Lemniscus & IC
DCN>>contra to Lat Lemniscus
CN Response Types
• Primary-like cell- spherical (bushy) cells of the
AVCN
• Chopper cell- identification with any particular
cell type is not possible because responses are
found throughout the cochlear nucleus
• Onset- located in octopus cells
• Pauser cell/ Build up cell- located in the fusiform
layer of the DCN
Pauser cell
Primary-like cell
Onset cell
Buildup cell
CN Response Types
Chopper cell
DCN Networking
• Intranuclear connex
– (largely inhibitory)
– Enhancing tuning?
• Outputs rising in lateral
lemniscus
– Predominantly contralateral
The Superior Olivary Complex
Connections To the Superior
Olivary Complex
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)
SOC Physiology
• Lateral SOC (EI and predominantly high freq)
– Max Response to large SPL diffs between ears
– Equal SPLs produce little activation
– Larger in animals with smaller heads
• Medial SOC (predominantly EE and low freq)
– Max Response to specific interaural time diffs
– Larger in man than in animals with smaller heads
Interaural Delay affects MSO
Synchronous Firing Rate
8
Spikes/Cycle
7
6
5
700 Hz
1300 Hz
4
3
2
1
0
-1.6
-1.2
-0.8
-0.6
-0.4
-0.2
0
0.2
Time Diff Between ears (ms)
0.4
0.8
0.35
0.3
Spike %age
0.25
0.2
0.15
Ipsi
0.1
Contra
0.05
0
0
0.3
0.5
0.7
% of Cycle
0.9
Lateral Lemniscus
• Tract of axons from just above SOC to IC
(originating from cell bodies in several
different structures)
• Has a Nucleus (Nucleus of LL)
– Good Temporal Resolution
• Involved in Startle Reflex
– Connection from CN to Pontine Reticular
Formation
– PRF >>motor neurons and spinal interneurons
Dorsal (back) Side of Brainstem
• Thalamus
(medial geniculate)
• Inferior Colliculus
• 4th Ventricle
• Area of Pons
Inferior Colliculus
Inferior Colliculus
• Cells respond to characteristic:
–
–
–
–
Interaural delays
Interaural amplitude differences
Amplitude modulations
Frequency modulations
• Integration of multi-modal sensory inputs
–
–
–
–
Adjacent visual nuclei
Proprioception of head and neck
Outputs include oculomotor nuclei
IC stim modifies activity in brain areas involved
in attention and learning.
Medial Geniculate Body
Thalamus
• Last Sensory Relay Station prior to Cortex
• Complex of nuclei
• MGB is mainly auditory
– But has other inputs as well
– AND
– Some other nuclei respond to aud. stim.
MGB
• Three Sub-divisions:
– Ventral MGB – True Auditory Relay nucleus
– Medial MGB – Auditory with Somatosensory
– Dorsal MGB –Somatosensory
Ventral MGB:
• Relay cells with overlapping dendritic “nests”
• Interneurons inhibit relay cells & other
interneurons
• Tonotopic Lows-lateral, highs-medial.
• Most (90%) Cells are binaural (EE or EI)
• 10% Monaural cells: contralateral excitation
Medial MGB:
• Cells have CF,
– Some show broad tuning
– Some have TWO CFs
• “Characteristic Intensity” in some cells
• EE, EI, IE
• All respond for duration of stim
– Little Adaptation
– But show Habituation
• Influenced by somatosensory inputs
Dorsal MGB
• Inputs
– From IC Both Aud. & Mixed
– From Superior Colliculus
– Somatosensory Afferents
• “Nonspecific” responses
Auditory Radiations Connect
• Medial Geniculate
Body (in purple)
to
• Primary Auditory
Cortex (in blue)
Primary Auditory Cortex (AI):
superior surface of the temporal lobe
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
Cortical Neurons
• Tonotopic
– Lows lateral
– Highs medial
• Spatiotopic
– (best responses from contralateral hemifield)
• Strong Habituation/Learning
• Sensitive to CHANGES in Frequency and
Intensity
Cortical Processing
•
•
•
•
Pattern Recognition
Duration Discrimination
Localization of Sounds
Selective Attention
Cerebral Dominance
• Most right-handed individuals show
distribution of 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