AUDITORY PATHWAYS

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AUDITORY PATHWAYS HEARING
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Auditory Projections
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Tonotopic Organization of A1
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Medial Geniculate Nucleus
Auditory Cortex
Inferior Colliculus
Cochlear Nucleus
Left Auditory Nerve
Superior Olive
Right Auditory Nerve
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Auditory Pathways
Medial Geniculate Nucleus
Auditory Cortex
Inferior Colliculus
Cochlear Nucleus
Superior Olive
Left Auditory Nerve
Right Auditory Nerve
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Auditory Pathways

• Auditory Nerve - Axons from hair cells
• Cochlear Nucleus - Sends information from the
  auditory nerve to the Superior Olive and to the
  Inferior Colliculus
• Superior Olive - Analogous to the Optic Chiasm -
  information from both ears crosses over to be
  sent to both hemispheres
• Inferior Colliculus - Analogous to the Superior
  Colliculus for vision - Orienting and reflexive
  localization -- recent studies show multimodal
  neurons in the colliculus which share visual and
  auditory information for orientation movements
• Medial Geniculate Nucleus (MGN) Relays
  information from the SO to A1

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Range of Hearing
20 50 100 200 500
1000 2000 5000 10000 Frequency (Hz)
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Range of Hearing
Range of speech sounds
20 50 100 200 500
1000 2000 5000 10000 Frequency (Hz)
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Audiogram
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Audiogram
critical for certain consonants
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Hearing Loss

• Conduction Deafness - any damage to the middle
  ear which impairs hearing
• Nerve Deafness or Presbicusis- Effects High
  Frequencies - Less elasticity in the Basilar
  membrane - Loss of nutrients to cochlea -
  Cumulative effects of noise
• Noise Exposure - Effects High Frequencies - Both
  Sudden and prolonged exposure
• When high Frequency hearing is impaired speech
  perception becomes increasingly difficult

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Auditory Impairments, Sensory Substitution
Treatments
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Types of Impairment

• Conduction Deafness
• Nerve Deafness
• Cortical Deafness

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Conduction Deafness

• Anything up to but not including the cochlea
• Obstructions
• Damage

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Treating Conduction Deafness

• Remove Obstruction
• Repair Eardrum
• Repair Ossicles
• Open Eustacian Tube

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Nerve Deafness

• Damage to the Cochlea, Or Path to Cortex
• Cilia or Hair Cells
• Basilar Membrane
• Auditory Nerve
• Olive
• Auditory Tract
• Inferior Colliculus
• MGN of Thalamus
• Auditory Projections

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Causes of Type I Nerve Deafness

• Presbycusis Old Ear -- High Frequency hearing
  loss
• Noise Induced Hearing Loss Also effects high
  frequencies Damage to cilia or Bassilar
  membrane -- Tinitus
• Infection of Cochlea Damage to cilia
• Meniers Disease Excessive fluid pressure in
  Cochlea damages Organ of Corti.

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Treating Type I Nerve Deafness

• Cochlear Implant

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Cochlear Implant Internal
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Cochlear Implant

• Recall that the cochlea is coiledAnd that the
  basillar membrane selects frequencies
• The electrode has multiple stimulation points
  that selectively activate nerves at the
  appropriate places

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Nerve Deafness

• Damage to the Cochlea, Or Path to Cortex
• Cilia or Hair Cells
• Basilar Membrane
• Auditory Nerve
• Olive
• Auditory Tract
• Inferior Colliculus
• MGN of Thalamus
• Auditory Projections

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Causes of Type II Nerve Deafness

• Degenerative nerve disease
• Congenital disorder
• Infection
• Stroke
• Trauma

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Treating Type II Nerve Deafness

• No cure at present
• Stem cells research is designed to allow new
  nerve growth in damaged areas.
• Has already worked with Parkinsons and
  Tourrettes
• Should work for vision, audition, Alzheimers,
  Epilepsy, stroke, etc.

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Summary of Nerve Deafness

• Caused by damage between cochlea and cortex
• Cochlear Implants
• Stem Cell Research

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Sensory Substitution

• ASL
• Closed Captioning Foundation