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At least 181 records · Page 10Linked to original sources
PubMed1999

Descending auditory pathways: projections from the inferior colliculus contact superior olivary cells that project bilaterally to the cochlear nuclei.

Multiple retrograde and anterograde tracers were used to characterize a pathway that extends from the inferior colliculus to both the left and right cochlear nuclei via a synaptic relay in the superior olivary complex. Different fluorescent tracers were injected into the left and right cochlear nuclei to identify cells in the superior olivary complex that project bilaterally. Double-labeled cells were present in almost all periolivary nuclei; the majority were located in the ventral nucleus of the trapezoid body and the anteroventral periolivary nucleus. Because these two nuclei are targets of descending projections from the inferior colliculus, triple-labeling experiments were performed to determine whether collicular axons contact the periolivary cells that project to the cochlear nuclei. The results demonstrate that descending axons from the inferior colliculus contact periolivary cells that project to the cochlear nuclei, including periolivary cells that project bilaterally. This pathway could provide an opportunity for higher levels of the auditory system to influence activity bilaterally in the cochlear nuclei and thus to modulate the initial processing of acoustic information by the brain.

Animals↗
PubMed1983

Ascending projections to the medial geniculate body of the cat: evidence for multiple, parallel auditory pathways through thalamus.

The sources of ascending input to the medial geniculate body (MGB) of the cat were studied using the retrograde transport of horseradish peroxidase (HRP). HRP injections were made iontophoretically through micropipettes which were also used to record physiological properties at the injection sites. This technique produced small injections which appeared to be restricted to single subnuclei. The tectothalamic projection of the auditory system was found to consist of at least four distinct and separate pathways. The ventral division of the MGB receives a topographical projection from the central nucleus of the inferior colliculus (ICC) which preserves tonotopicity and provides short latency, sharply frequency-tuned responses. The medial part of the ICC projects to the deep dorsal nucleus, which contains only units tuned to high frequencies. The major inputs to the caudodorsal nucleus (DC) stem from nucleus sagulum and the pericentral nucleus of the inferior colliculus (ICP). Units in DC and the ventrolateral nucleus, which also receive input from ICP, have very broad tuning properties and late, habituating responses. Injections of HRP into the medial division (MGM) produced labeled cells scattered throughout the external nucleus of the inferior colliculus and the ventral part of ICC. This widespread input is reflected in the wide range of auditory responses found in MGM. Auditory responses in the suprageniculate nucleus were poorly defined and many units did not respond to tonal stimuli; following HRP injections no filled cells were found in the inferior colliculus, but labeled cells were found in the deeper layers of the superior colliculus and in the interstitial nucleus of the brachium of the inferior colliculus. Together with recent findings on the auditory thalamocortical projection, these results provide evidence for multiple parallel auditory pathways through the thalamus.

Afferent Pathways↗
PubMed1981

Phase reversal in brain stem responses: its use in the detection of asymmetry in the auditory pathways.

Electrode placement is an important consideration in the recording of a large-amplitude stable response. In this study, brain stem auditory-evoked potentials (BAEP) were obtained from subjects and patients under two electrode configurations, namely 'vertex-mastoid' and 'mastoid-mastoid'. The BAEP waveforms to ipsilateral, contralateral and binaural stimulation were examined for their phase relation with respect to stimulation. In the mastoid-mastoid recording mode, a complete polarity reversal was shown upon changing stimulation from the ipsilateral (with respect to the active input) to the contralateral ear. On simultaneous binaural stimulation, the response was shown to summate to zero. This observation has led to the objective assessment of asymmetry of hearing. Several patients exhibiting recruitment were tested under the mastoid-mastoid recording configuration with binaural stimulation. The results show that a summated 'null' response only occurs at an intensity level where loudness equality is attained at the two ears and recruitment is complete. Applied in this way the technique has promising application in the determination of the presence or absence of recruitment and hence in the differential diagnosis of cochlear and retrocochlear lesions.

Auditory Pathways↗
PubMed1998

Functional neuroanatomy of auditory pathways in the sound-producing fish Pollimyrus.

We have described the acoustic pathway from the ear to the diencephalon in a sound-producing fish (Pollimyrus) based on simultaneous neurophysiological recordings from single neurons and injections of biotin pathway tracers at the recording sites. Fundamental transformations of auditory information from highly phase-locked and entrained responses in primary eighth nerve afferents and first-order medullary neurons to more weakly phase-locked responses in the auditory midbrain were revealed by physiological recordings. Anatomical pathway tracing uncovered a bilateral array of both first- and second-order medullary nuclei and a perilemniscal nucleus. Interconnections within the medullary auditory areas were extensive. Medullary nuclei projected to the auditory midbrain by means of the lateral lemniscus. Midbrain auditory areas projected to both ipsilateral and contralateral optic tecta and to an array of three nuclei in the auditory thalamus. The significance of these findings to the elucidation of mechanisms for the analysis of communication sounds and spatial hearing in this vertebrate animal is discussed.

Animal Communication↗
PubMed1990

Rate fluctuations and fractional power-law noise recorded from cells in the lower auditory pathway of the cat.

The noise properties of the sequence of action potentials recorded from adult-cat auditory nerve fibers and lateral superior olivary units have been investigated under various stimulus conditions. Large fluctuations exhibited by the spike rate, and spike clusters evident in the pulse-number distribution, both indicate an unusual underlying sequence of neural events. We present results demonstrating that (i) the firing rate calculated with different averaging times can exhibit self-similar behavior; (ii) the pulse-number distribution remains irregular even for large numbers of samples; (iii) the spike-number variance-to-mean ratio increases with the counting time T in fractional power-law fashion for sufficiently large T; and (iv) the exponent in the power law generally depends on the stimulus level. The results obtained in our laboratories support the notion that all auditory-nerve and LSO units exhibit fractal neural firing patterns, as indicated earlier by Teich (IEEE Trans. Biomed. Eng. 36, 150-160, 1989).

Action Potentials↗