Dynamic changeDynamic change

Dynamic change: the range of stimulus levels Dynamic change: the range of stimulus levels over which a change in level produces a over which a change in level produces a change in a neuron’s discharge ratechange in a neuron’s discharge rate

Dynamic range of ANF: <35 dB at CFDynamic range of ANF: <35 dB at CF

DR reduced when embedding in noisy DR reduced when embedding in noisy backgroundbackground

Human can discriminate 100-dB range of stimuHuman can discriminate 100-dB range of stimulus (behavior test)lus (behavior test)

Possible reasons: Possible reasons: Olivocochlear efferent systOlivocochlear efferent systemem

Hypothesis:Hypothesis: sound-evoked efferent activity ma sound-evoked efferent activity may exert an greater influence on DR in y exert an greater influence on DR in awake anawake animalsimals than in anesthetized ones than in anesthetized ones

PSTH from single-unit in PSTH from single-unit in VCNVCN

Pri-Notch

Pri-like

Chopper UnitsOnset Un

it

Dynamic RangeDynamic Range

Comparison of DRComparison of DR (in quiet environment)(in quiet environment)

Noise-inducedNoise-induced shiftshift of CF rate-level function (from VCN chopper of CF rate-level function (from VCN chopper unit)unit)

Noise-induced horizontal shift

Larger shift at awake cats (p< 0.0001)

Noise-inducedNoise-induced shiftshift (cont)(cont)

Chopper < pri-like at lower level

Awake chopper vs awake pri-like vs anesthetized

Noise-induced Noise-induced compressioncompression

Anesthetized cats could not respond at background of >50 dB because of saturation

Less compression in awake cats

Adaptation in noisy Adaptation in noisy environmentenvironment

Adaptation

SR

Noise-induced Noise-induced compressioncompression

Awake chopper vs awake pri-like vs anesthetized

Noise-induced Noise-induced shiftsshifts & & compressioncompression:: AwaAwake vs Behavingke vs Behaving

SummarySummary

Larger shift & less compression: higher DLarger shift & less compression: higher DR in R in VCN units of awake catsVCN units of awake cats than in than in ANANFs in anesthetized catsFs in anesthetized cats or or VCN units in dVCN units in decerebrate catsecerebrate cats

Otherwise most characteristics are similaOtherwise most characteristics are similar (awake vs anesthetized in quite, PST rer (awake vs anesthetized in quite, PST response type)sponse type)

Explanation: the cochlea and auditory nerExplanation: the cochlea and auditory nerve are unaffected by anesthesia. ve are unaffected by anesthesia.

Olivocochlear systemOlivocochlear system (or other descen (or other descending systems) could very well be affected ding systems) could very well be affected by anesthesia by anesthesia

Descending systems are important for intDescending systems are important for intensity coding and detection in backgrounensity coding and detection in background noise. d noise.

COCB effects on ANF of COCB effects on ANF of anesthetized catsanesthetized cats

With COCB stimulation, higher Shift & lower compression higher DRWinslow et al 1987