Lecture 11 - Auditory System (Part 2) - Central Processing and Perception

Question 1

Once and electrical signal is transduced via the cochlear nerve how many synaptic pit stops are there? leading to the auditory cortex or A1

Answer 1

-four obligatory pit stops and one optional pitstop

1. cochlear nucleus (brainstem)
2. superior olive (optional)
3. inferior colliculus (midbrain)
   4.Medial Geniculate Body (thalamus)
4. Primary auditory cortex (temporal lobe)
   (after reaching A1 there are association areas surrounding Heschl’s gyrus where A1 is found where further auditory processing occurs)

Question 2

In the first obligatory synapse the cochlear nucleus where is it located and how many divisions does it have?

Answer 2

-located between the medulla and pons
-two divisions - dorsal cochlear nucleus and the anterior ventral cochlear nucleus

Question 3

What does the DCN or the dorsal cochlear nucleus division do?

Answer 3

primary auditory processing and projects directly to the inferior colliculus in the midbrain (skips the superior olive)

Question 4

What does the AVCN or the anterior ventral cochlear nucleus do?

Answer 4

responsible for sound localization and binaural processing which includes Bushy cells which project to the medial and lateral superior olive
-these cells also receive direct input from the cochlear nerve via unique synaptic terminal known as the end bulb of held

Question 5

AVCN fibers project to the superior olive which is the second overall synaptic pit stop first optional pit stop and what are the two response types and two divisions of the superior olive?

Answer 5

Response Types - EE and EI
Divisions - Medial Superior Olive MSO and Lateral Superior Olive LSO
-EE is a subset of neurons which respond to auditory stimuli from both ears
-EI subset of neurons which respond to auditory stimuli from contralateral ear
-MSO - send outgoing efferent fibers to the OHCs in the cochlea to adjust the tension of the tectorial membrane
-LSO - receive incoming afferent fibers from the IHCs in the cochlea

overall - MSO OHCs
LSO - IHCs

Question 6

Where is the inferior colliculus synaptic pitstop found and how many divisions does it have?

Answer 6

-found in midbrain
-divisions: central nucleus, dorsal cortex, lateral cortex

Question 7

What does the inferior colliculus do?

Answer 7

sound localization and has a tonotopic map from the cochlea

Question 8

What does the central nucleus of the inferior colliculus do?

Answer 8

-it is tonotopically organized and it serves as the core nucleus of the inferior colliculus

Question 9

What does the dorsal cortex of the inferior colliculus do and how many layers does it have?

Answer 9

-it has four cortical layers and it is polymodal meaning it receives info from the spinal cord to participate in auditory and somatosensory processing

Question 10

What does the lateral cortex of the inferior colliculus do and how many cortical layers does it have?

Answer 10

three layers; involved in visual and auditory processing by receiving info from the superior colliculus

Question 11

What does the medial geniculate body or MGB form and how many independent divisions does it have?

Answer 11

-forms the auditory thalamus
-has four independent divisions - ventral MGB, dorsal MGB, medial MGB, and suprageniculate MGB

Question 12

What is the ventral MGB involved in?

Answer 12

tonotopically organized and involved in only auditory processing

Question 13

What is the dorsal MGB involved in?

Answer 13

involved in auditory and somatosensory processing

Question 14

What is the medial MGB involved in?

Answer 14

auditory and limbic processing because it is close to the amygdala

Question 15

What is the suprageniculate MGB involved in?

Answer 15

auditory and higher cognitive processing

Question 16

Where is the primary auditory cortex found?

Answer 16

in Heschl’s gyrus of the temporal lobes

Question 17

Where do the efferent projections of the primary auditory cortex target?

Answer 17

they target the secondary auditory cortex or A2

Question 18

What is the tonotopic representation of A1?

Answer 18

high frequencies are caudal
low frequencies are rostral

Question 19

What is the columnar organization of the primary auditory cortex?

Answer 19

each row represent binaural preference and each column represents frequency preference

Question 20

Where and what do the higher order association areas that receive auditory information are and do?

Answer 20

-they are beyond the primary and secondary cortex and they receive auditory information

Question 21

What are some if the association cortical targets from A1 and A2?

Answer 21

the limbic cortex - parietal lobes, amygdala, insula, cingulate cortex
language network - broca’s and wernicke’s area
-hippocampus - auditory memory
-motor cortex - responding to auditory stimuli through motor movement

Question 22

What are the two mechanisms used by the superior olive for sound processing?

Answer 22

ITD - interaural time difference
ILD - interaural Intersity Level Difference

Question 23

In what type of animals is ITD more effective?

Answer 23

-animals with larger heads meaning greater distance between ears

Question 24

What do delay lines do?

Answer 24

they extend from bushy cells in the AVC and they must travel different distances to reach each ear creating a time difference between the ears

Question 25

What part of the superior olive is involved in ILD?

Answer 25

lateral superior olive and in bats the medial nucleus of the trapezoid body

Question 26

What type of sound is ILD most effective with and why?

Answer 26

high frequency sounds since they are affected by an acoustic shadow in which the ipsilateral ear experiences a greater intensity of sound that the contralateral ear

Question 27

What is a cochlear implant?

Answer 27

replaces the organ of corti and has a tonotopic map