Week 8 (Auditory Processing in the Brain, Deafness, Old Age, Music)

Auditory Processing in the Brain

  • Once auditory information is coded in the cochlea that information goes to the hindbrain

    • First it goes to the ipsilateral (same side) cochlear nucleus

    • Then information goes to the contralateral (opposite side) cochlear nucleus

    • Then information goes to the contralateral superior olive

  • The hindbrain information goes to the inferior colliculus in the midbrain

  • It is then sent to the medial geniculate nucleus of the thalamus

  • The finally to the primary auditory cortex (temporal lobe)

    • Information from the right year go to the left auditory cortex and vise verse

Auditory Cortex

  • The superior temporal gyrus contains the primary auditory cortex

    • Also known as Heshcl’s gyrus or A1

    • Responds to real and imagined sounds

    • Unlike vision damage to A1 does not lead to deafness

Sound Localization

  • Sound localization is the ability to recognize where in space a certain auditory stimulus came from

  • This process relies on comparing the auditory responses from both ears

    • Time of arrival

      • Comparing the time of arrival is useful for localizing sounds with a sudden onset

      • The superior olive helps compare the timing for auditory stimuli in both ears

    • Sound shadow

      • Comparing the difference in sound intensity can help localize sound

      • Especially for high frequency sounds

      • High pitch sounds have shorter wavelengths than the head, so the head creates a sound shadow

    • Phase difference

      • Comparing the difference in sound wave phases can help localize sounds

      • Especially for low frequencies

Deafness

  • Two many categories of hearing loss

    • Conductive deafness (middle ear deafness)

    • Cannot transmit sounds properly to the cochlea

    • Can be corrected by surgery or hearing aids by amplifying the auditory stimulus

      • Damage to ossicles

    • Nerve deafness (inner ear deafness)

      • Damage to the cochlea, hair cells, or auditory nerve

      • Can be inherited

      • Often produces tinnitus

      • More difficult to correct

Cochlea Implants

  • Bypass damaged hair cells by converting sound waves into electrical signals carried by electrodes into cochlea which excites auditory nerve

    • Does not restore normal hearing

    • Difficulty filtering different sounds

Hearing and Old Age

  • Older people often have hearing problems even if they use hearing aids

  • Two main factors play in this

    • Decreased inhibitory neurotransmitters in the auditory system in old age

    • The ability to filter out information becomes increasingly difficult

  • They often even have hearing problems even if they use hearing aids

    • Brain area responsible for language comprehension are less active in old age

    • Could be natural deterioration or a reaction to less auditory input 

Musical Talent

  • Amusia is the impaired ability to detect pitch changes

    • Tone deafness

    • Likely has a genetic component

      • Fewer connections from the right auditory cortex to the frontal lobe

  • Absolute pitch refers to the ability to hear a note and identify it

    • Genetics contribute, but early age musical training is usually necessary

    • Not everyone with musical training develops absolute pitch

    • More common in people who speak tonal language