28b. brain mechanisms

Question 1

What is the first structure in the auditory pathway after the auditory nerve?

Answer 1

cochlear nucleus

Question 2

Auditory nerve fibers carry signals from each ear to the ____ cochlear nucleus.

a. ipsilateral
b. contralateral

Answer 2

a. ipsilateral

Question 3

What are the 3 places that the MAIN pathways go after the cochlear nucleus? Are they ipsilateral or contralateral?

Answer 3

1. inferior colliculus
2. superior olivary complex
3. trapezoid body –> SOP^

Question 4

After the auditory nerve, what are the 5 steps for the main pathway(s)?

Note when it becomes contralateral

Answer 4

1. Cochlear nucleus (ipsilateral)
2. Superior olivary complex (CL)
3. Inferior colliculus (CL)
4. Medial geniculate body (CL)
5. Auditory cortex (CL)

• sometimes its trapezoid body –> SOP

Question 5

What are descending pathways? Why do we know less about them?

Answer 5

• pathways that carry signals from the primary auditory cortex (A1), to subcortical structures, to the ears
• we know less because they’re rather inactive when the animal is under anesthesia, as is usually the case during these studies

Question 6

3 examples of things descending pathways do?

Answer 6

1. inhibitory signals reduce the motile response in outer hair cells
2. acoustic reflex
   - prevent damage to ears
   - contract muscles around ossicles to limit their movement
   - this reduces the amplification, prevents overstimulation of cochlea
3. involved in attention
   - block auditory signals that are irrelevant to the task / attention
   - allow signals that are relevant

Question 7

Where is the auditory cortex?

Answer 7

• on top of the temporal lobe

Question 8

• What structure is the auditory core region located within?
• What 2 (paired ish) structures surround it?

Answer 8

• situated within the transverse temporal gyrus (AKA Heschl’s gyrus)
• surrounded by the belt and parabelt

Question 9

What 3 areas make up the auditory core region?

Answer 9

• Primary auditory cortex (A1)
• rostral core
• rostrotemporal core

Question 10

Auditory cortex:
Part of___, on top of ___, consists of…?

Answer 10

• part of cerebral cortex
• on top of temporal lobe
• consists of auditory core region, belt, and parabelt

Question 11

Neurons in the auditory core region are organized in a ____

Answer 11

• tonotopic map

Question 12

Tonotopic map def? Similar to…

Answer 12

• arrangement of neurons such that the characteristic frequencies of the neurons gradually shift from LOW (at one end of the region) TO HIGH (at the other end)
• similar to how visual cells were organized in columns by orientation

Question 13

Where does the process of discrimination and recognition of sounds happen?

Analogous to what visual structures?

Answer 13

• in the belt and parabelt
• areas BEYOND V1
  –> V4, MT, inferotemporal cortex

Question 14

Broader tuned neurons are thought to be helpful for…?

Answer 14

• discriminating and recognizing component frequencies of COMPLEX sounds

Question 15

“What” pathway?

Answer 15

• ventral
  (everything’s front)
• anterior auditory core region –> anterior temporal cortex –> prefrontal cortex

Question 16

“Where” pathway?

Answer 16

• dorsal
  (everything’s back)
• posterior auditory core region –> posterior temporal cortex –> Parietal cortex