l7 Flashcards
phase locking low vs high frequency
low- neurons phase lock and fire at each phase of cycle
- gives additional information about timing
high- cannot keep up to phase lock instead use tonotopy
how are APs conveyed on a ms time scale
action potential takes longer
- how can we compete faster if input to brain is slower
- because whole population gives informaiton not just 1 neuron
3 cues for sound localization
distance (forward and backward)
elevation (veritcal) most difficult to locate
azimuth *horizontal)
cue 1- direct/reflection ratio
direct- if someone is close by
reflection- if someone is far away sound reflects off surfaces
compare frequencies of direct/reflect to tell how far they are
(must be in enclosed room)
cue 2- loudness
distand sounds hav elower loudness than close ones
cue 3- sound spectrum
high frequencies are more quickly dampened by the air than low
- distant sound source sounds more muffled
cue 4- movement
when listener is moving, sound sources pass by faster than distanct sound sources
cues for horizontal localization
monoaural cues - 1 ear
bilateral cues-
interaural time difference
interaural level difference
vertical cues
pinna viltering
interaural time difference measuring
for sound source infront: ITD = 0
can accurately localize 1 degree
directly to the side: around 600us diff (size of head)
can accurately localize 15 degrees
formula for ITD
time = distance/speed
= .20m/343m/s = 0.00000058 or 600us
jeffress model
coincident input is required for activation: binaural inputs converge
- axonal path length differences cause specific delay
- when neural delay is offset by ITD of the same magnitude the coincidence occurs and cell fires
- only at a ceratin ITD
AVCN axons
nucleus laminers in auditory systtem of owls shows shows evidence for delay lines in neurons on one side and not in the other
medial superior olive
where comparison is thought to happen in mammalian brain- bushy cells synapse from hair cells and sendoinput to MSO
- also have contralateral delay lines from cochlea on oppsoite side
- excited by ipsilateral and contra AVCN
- inhibited by MNTV and LNTB
expermental ITD
placed animal in sound proof room and recorded from auditory brain stem
- change time difference in sound to stimulate positions
neural response vs interaural time difference graph
when ear leads by too much there is no response, as it gets closer you see response
- positive ITD then you see firing
- neurons sensitive to small window time (200us)
interaural phase difference
ONLY LOW FREQUENCEIS- needs to phase lock
transient: difference in time of arrival of first wavelength at two ears
sustained: on going time differences
periodic ITDs in MYSO
vary delays- doesnt like 500ms but like 1100, doesnt like 1500 this is because delay corresponds to certain phase phases and it repeats over and over, get a cyclical characteristic response
varying frequencies at MSO
perodicity oc cycles now varies because each frequency will come in and out of phase at diff times
low freq- longer
high freq- shorter
have same best delay no matter what frequency (if not optimal freq you get lower repsonses)
MSO frequency tuning
lower frequencies mostly
- tonotopically organized emphasizing low frequencies
- dorso-ventral tonotopic gradient
- high freqs ventral
head shadow- localization cue
high frequencies take advantage of second factor - interaural intensity difference due to head shadow
ILD of LSO & MNTB
excited by ipsilateral ear (globular bushy cells)
inhibited by contralateral ear (globular bc)
binaural suppression
calyx of held
largest synapse in brain
lateral superior olive
majority of cells receive excitatory input from VCN, inhibitory input from contra VCN via ipsi MNTB
e and i inputs have identical spectral receptive fields
what is respone determined by
balance between excitation and inhibition
response = excitation - inhibition
MSO vs LSO frequencies
MSO- low
LSO- high
mso outputs
DNLL and ICC (dorsal low frequency)
LSO outputs
bilaterally:
- excitatory projections to DNLL and ventral ICC on contralateral
inhibitory projections to DNLL and ICC on ipsilateral
