Perception of infrasound: Difference between revisions

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Infrasound sensitive fibers have very high rates of spontaneous discharge, with a mean of 115imp/s, which is much higher than the spontaneous discharge of other auditory fibers.<ref name="Schermuly 1990a" /> Recordings show that discharge rates do not increase in response to infrasound stimuli but are modulated at levels comparable to the behavioral thresholds.<ref name="Schermuly 1990a" /> Modulation depth is dependent on stimulus frequency and intensity. The modulation is phase locked so that the discharge rate increases during one phase of the stimulus and decreases during the other, leaving the mean discharge rate constant.<ref name="Schermuly 1990a" /> Such pulse-frequency modulation allows the stimulus analysis to be independent of the peripheral tuning of the [[basilar membrane]] or the [[hair cells]], which is already poor at low auditory frequencies.<ref name="Schermuly 1990a" /> Unlike other acoustic fibers, infrasonic fibers do not show any indication of being tuned to a particular characteristic frequency.<ref name="Schermuly 1990a" />

By injecting fibers that were identified to be sensitive to infrasound with HRP (Horseradish Peroxidase), the ___location and morphology of the stained fibers can be observed in sections under a microscope. Infrasound sensitive fibers are found to be simple bipolar cells in the [[auditory ganglion]] with a diameter of 1.6-2.2&nbsp;µmμm at the axon and 0.9-1.2&nbsp;µmμm at the dendrites.<ref name="Schermuly 1990b">{{cite journal |last=Schermuly |first=L. |author2=R. Klinke |title=Origin of infrasound sensitive neurones in the papilla basilaris of the pigeon: an HRP study |journal=Hearing Research |year=1990 |volume=48 |issue=1–2 |pages=69–78 |doi=10.1016/0378-5955(90)90199-y|pmid=1701169 |s2cid=4761698 }}</ref> They originate in the apical end of the cochlea and they are located near fibers that transmit low frequency sounds in the acoustic range. Unlike the ordinary acoustic fibers which terminate on the neural limbus, the infrasonic ones terminate on cells on the free basilar membrane.<ref name="Schermuly 1990b" /> Furthermore, infrasonic fibers terminate on 2-9 hair cells while normal acoustic fibers connect to only one.<ref name="Schermuly 1990b" /> Such characteristics would make these fibers analogous to fibers connecting to the outer hair cells in mammals, except that mammalian outer hair cells are known to have efferent fibers only and no afferents.<ref name="Schermuly 1990b" /> These observations suggest that the infrasound sensitive fibers are in a class separate from ordinary acoustic fibers.

== References ==