2 - Identifying auditory cortical areas

Question 1

What is a tonotopy?

Answer 1

The spatial arrangement of where sounds of different frequency are processed in the brain

Question 2

How can you do an fMRI study focused on tonotopy without the scanner noise interfering?

Answer 2

By utilizing sparse sampling. By changing up the time interval between the stimulus and the scan that way you collect information at different points of the BOLD response curve. This is only possible thanks to the metabolic delay.

Question 3

Where is the auditory core located?

Answer 3

It is located at the Heschl’s gyrus.

Question 4

What is a best frequency map?

Answer 4

A map of the brain on which the frequency that evoked the highest BOLD response is indicated in color.

Question 5

Give convincing evidence for an auditory hierarchy

Answer 5

The sensitivity of the core and belt differs. The core is activated by single-frequency tones and the belt is activated by noise bursts aka complex sounds. Therefore the belt is involved in higher-order auditory processing.

Question 6

What is the lemniscal classical auditory pathway?

Answer 6

This pathway is tonotopically organized throughout. This includes the central nucleus of inferior colliculus and ventral division of medial geniculate body. It projects to the core.

Question 7

What is the extralemniscal non-classical pathway?

Answer 7

It has diffuse frequency organization and provides aspecific sensory information. It includes the inferior colliculus and dorsal and magnocellular subdivisions of medial geniculate body. It projects to the belt.

Question 8

What are the 3 approaches to deal with sound intensity?

Answer 8

• Adjust sound intensity levels to a fixed level above subjects’ behaviorally measured hearing thresholds, per frequency
• Adjust intensity levels according to standard equal loudness curves
• Let subjects behaviorally match the loudness of each test frequency used