Auditory Cortex Flashcards
1
Q
Outline the pathway for auditory processing
A
- first central synapse is in the cochlear nuclei of the medulla
- complex synaptic network in brainstem
- projection to primary auditory cortex via thalamus(medial geniculate nucleus MGN also called medial geniculate body MBG. or complex)
◦ lateral geniculate nucleus for vision
2
Q
What mediates the sound source localisation?
A
Network of brainstem nuclei
- organisation of brainstem auditory nuclei suggests complex processing
- ascending projections of auditory brainstem (above cochlear nuclei) show high degree of bilateral connectivity
- best understood function is sound localisation
3
Q
What does spatial localisation depend on?
A
◦ interaural time differences
◦ interaural intensity differences
‣ requires comparison of sounds from the two ears
4
Q
Describe the interaural time differences for sound source localisation
A
Jeffries Model
- medial superior olivary (MSO) receives inputs from left and right AV cochlear nucleus
- longest interaural time differences around 700 microseconds
- psychophysics indicates differences can be detected as short as 10 microseconds
- time differences used for computing location for sound frequencies up to 3kHz
- assume there is a delay in transmission to the medial superior olivary upon arrival time of sound
- neurons will be tonotopically arranged but are selective to diff interaural time delays
- sound reaches left ear first and activate cochlear then reaches dorsal cochlear nucleus
- same thing happens from other ear, but reaches ear slightly later (if sound further away from the right ear)
- post synaptic neurons are coincidence detectors
◦ generate spike when presynaptic AP arrive simultaneously from left and right ear - AP will reach neuron A via neuron 1 of left ear before neuron 5 of right ear
◦ results in matchpoint
5
Q
What does interaural time difference require?
A
Precise spike timing
- AN afferents can phase lock in low-mid frequency range
- class of cells in anteroventral cochlear nucleus (bushy cell) show even stronger phase locking
- AVCN orjects to MSO potentially providing precise timing information
