Auditory system: Processing

temporal coding/frequency theory

The basilar membrane vibrates at the frequency of sound, and hair cells drive APs at the same rate

• goes up to 1000Hz

• 1ms refractory period

Volley principle

groups of neurons that fire in alternation on different cycles when a sound is too high for the refractory period

• This works up until 4000 Hz

Place coding

Each hair area in the basilar membrane corresponds and resonates with a certain frequency

• similar to labeled line strategy

• base for thin/high frequencies

• apex for low/floppy frequencies

Auditory pathway

1. cochlea

2. vestibular nerve (cranial nerve VIII)

3. Cochlear Nucleus (in the brain stem)

4. travel contralaterally to the superior olivary nucleus (SON)

5. inferior colliculus

6. Medial Geniculate Nucleus (MGN)

7. to cortical regions needed for audio processing

Superoir Olivary Nucleas (SON)

located in the Pons, processing input from both ears to locaize sound in space

Inferoir colliculus

plays a role in sound localization

Medial Ganiculate Nucleus (MGN)

audiotory relay nucleus in the thalamus

Primary Audio Cortex (A1)

Located in the superior region of the temporal lobe; discriminates and interprets complex sounds (most sounds)

• One in each hemisphere; processes contralateral information

streams of audio processing

1. dorsal path

2. ventral path

Dorsal path

projects to the parietal complex; focuses on spatial localization and head movements (movement and positioning)

Ventral path

projects to temporal lobe; interprets what complex sounds are (most things)