Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Inferior Colliculi”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 595 records · Page 33Linked to original sources
PubMed1983

Effects of age upon auditory evoked potentials from the inferior colliculus and cortex in the guinea pig.

Auditory evoked potentials from the inferior colliculus and cortex were examined for evidence of the effect of aging in central regions of the auditory system of the guinea pig. The threshold was 25 dB higher in the responses from the inferior colliculus and 44 dB higher in the cortical potentials in old animals than in young animals. The latency of the collicular responses in the old group was greater by 1.5 ms and, in the high-frequency range, the amplitudes were smaller at all intensities tested. The latency of responses recorded from the auditory cortex in the old guinea pigs was 3.6 ms greater at threshold and the amplitudes were smaller. With stimuli well above threshold, the latency differences were no longer significant, whereas the amplitudes in old animals became significantly greater than those in the young.

Age Factors↗
PubMed1978

Effect of high-intensity sound on cochlear microphonics and activity of inferior colliculus neurons in the guinea pig.

The input-output functions of cochlear microphonics (recorded from the round window) in guinea pigs exposed briefly to high-intensity sound (2 kHz, 130 dB, 30 min) were shifted toward higher intensities by about 15 dB in comparison with normal animals. 2-4 h after the exposure this shift decreases to 10 dB. The response characteristics of the inferior colliculus neurons were compared under similar conditions. Thresholds at the characteristc frequencies (CF) measured 2-4 h after exposure, were raised by 30-50 dB, a higher threshold increase was observed at frequencies from 5-7 kHz. 48 h after exposure the thresholds approached those obtained in normal animals. There was no pronounced hair cell loss after exposure. It is assumed that in addition to the impairment of sound transduction in hair cells there may be a specific effect of high-intensity sound exposure on neuronal transmission in the auditory pathway.

Animals↗
PubMed1987

The postnatal development of stimulated deoxyglucose uptake into the mouse cochlea and the inferior colliculus.

The effect of acoustic stimulation on the postnatal development of deoxyglucose uptake into the mouse cochlea and the inferior colliculus was evaluated. Animals between postnatal day 4 and 20 were separated into four different groups depending on their age. Tritiated deoxyglucose was injected intraperitoneally into each animal and tracer uptake was quantitated by microdissection of the tissues and scintillation counting. Acoustic stimulation at a noise level of 100 dB (A) resulted in supra-normal levels of deoxyglucose uptake for all auditory tissues during postnatal days 13, 14, and 15. The lateral wall tissues, which are non-sensory and non-neuronal, also increased deoxyglucose uptake following acoustic stimulation in a manner that paralleled the uptake by the sensory structures. Serum radioactivity and glucose levels remained unchanged during postnatal development, with these parameters remaining stable with acoustic stimulation.

Acoustic Stimulation↗
PubMed1995

The role of the inferior colliculus in a genetic model of audiogenic seizures.

Previous studies have shown the functional importance of the inferior colliculus (IC) for the propagation and initiation of audiogenic seizures in several models of epilepsy in rats. A review of the cell types and cytoarchitecture of the IC, including its three major subdivisions, is presented. Significant increases in GABA levels and the number of GABAergic neurons are found in the central nucleus of the IC (ICCN) of genetically epilepsy-prone rats (GEPR-9s) as compared to Sprague-Dawley rats that do not display audiogenic seizures. Two independent anatomical methods were used to determine the number of GABAergic neurons, immunocytochemistry and in situ hybridization. In both types of preparation, the labeled cells in the ICCN appeared to be of different sizes but the number of small cells with diameters less than 15 microns showed the greatest increase. Nissl-stained sections showed that the total number of neurons in the ICCN was increased in GEPR-9s and indicated that the increase in GABAergic neurons was not due to a change in the phenotype of collicular neurons from non-GABAergic to GABAergic. The number of small neurons in Nissl-stained sections of the ICCN was shown to correlate with seizure severity in the offspring of crosses made between Sprague-Dawley rats and GEPR-9s. Furthermore, the GEPR-3s that display moderate seizures showed a significant increase in the number of small neurons in the ICCN, and the magnitude of this increase was predicted from this correlation. Finally, the use of knife cuts through the midbrain indicated that the ICCN sends an important projection to the external nucleus and that this projection plays a vital role in the propagation of seizure activity from the site of seizure initiation in the ICCN. It remains to be resolved how the increase in small GABAergic neurons in the ICCN is responsible for the known pharmacological defects observed at GABAergic synapses.

Acoustic Stimulation↗
PubMed1995

Morphological classification and identification of neurons in the inferior colliculus: a multivariate analysis.

In this paper a modern statistical method is applied to an old cell classification and identification problem in the central nucleus of the inferior colliculus. In a recent computer-based reconstruction study of Golgi-impregnated neurons in the rat, two types of cell with flattened dendritic arbors, flat (F) and less flat (LF), were defined. Both types contributed to the anisotropic and laminar pattern of the nucleus. The classification was based on five morphological features of complete dendritic arbors, two assessed visually and three numerically. With respect to the latter criteria, the two types were classified by preselected cut-off values. The distinction of the two types was supported, among other things, by a prevailing spatial segregation into laminar and interlaminar compartments. The cell sample was too small, however, to validate the classification and segregation definitively. In the present study, the classification is tested by the partial least squares regression method which is independent of the preselected cut-off values, and is able to handle small sample sizes and interdependent variables. In the plots, the F and LF cells are clearly separated into two distinct clusters, strongly supporting the distinction of the two types. The different density of the two clusters shows that the F cells are more homogeneous that the LF cells. The relative importance of the classification criteria is also evaluated. The three-dimensional (3D) inspection and the 3D convex hull-based form factor were found to be the most powerful criteria for identifying the two cell types, while the 2D evaluation of camera lucida drawings, a standard method in neuroanatomy, proved to have the least predictive value.

Animals↗
PubMed1982

Optokinetic, vestibular, and optokinetic-vestibular responses in albino and pigmented rats.

Horizontal eye movements and neuronal activity in the vestibular nuclei and pretectum were recorded in albino and pigmented rats in response to optokinetic, vestibular (VS), combined visual-vestibular (VVS) sinusoidal stimulations. 1. VOR slow phase velocity in VS condition leads head velocity. This phase lead is smaller in albino than in pigmented rats. 2. Presence of vision (VVS) improves the phase angle of the VOR in both strains, especially at low frequencies. In pigmented rats the VOR is perfectly compensatory with respect to phase at all frequencies whereas in albinos the eye velocity still leads the head velocity. 3. There is no difference in the response characteristics of vestibular nuclear neurons (VN) to VS between albino and pigmented rats which could explain the difference in their VORs. 4. In the pigmented rat, there is a strong optokinetic input to VN which provokes a shift of the response peak towards peak head velocity. These visual-vestibular interactions at VN level are in agreement with the changes in the phase angle of the VOR. 5. In albino rat, there are no differences in the response characteristics of VN between VS and VVS, thus the decrease of the VOR phase lead observed in VVS compared to VS is due either to visual-vestibular interactions outside of the vestibular nuclei or to some general arousing effect of light. 6. Recording of responses of pretectal neurons to visual stimulation in albino rats has shown that they are activated in a phasic or tonic way by light on ("On cells") or off ("Off cells"). Contrary to the pigmented rat, pretreated neurons in albino exhibited no detectable direction specific optokinetic responses.

Animals↗
PubMed1989

Ontogenesis of tonotopy in inferior colliculus of a hipposiderid bat reveals postnatal shift in frequency-place code.

The postnatal development of midbrain tonotopy was investigated in the inferior colliculus (IC) of the south Indian CF-FM bat Hipposideros speoris. The developmental progress of the three-dimensional frequency representation was determined by systematic stereotaxic recordings of multiunit clusters from the 1st up to the 7th postnatal week. Additional developmental measures included the tuning characteristics of single units (Figs. 3f; 4f; 5f), the analysis of the vocalised pulse repertoire (Figs. 3e, 4e, 5e), and morphometric reconstructions of the brains of all experimental animals (Fig. 1). The maturation of auditory processing could be divided into two distinct, possibly overlapping developmental periods: First, up to the 5th week, the orderly tonotopy in the IC developed, beginning with the low frequency representation and progressively adding the high frequency representation. With regard to the topology of isofrequency sheets within the IC, maturation progresses from dorsolateral to ventromedial (Figs. 3c, 4c). At the end of this phase the entire IC becomes specialised for narrowly tuned and sensitive frequency processing. This includes the establishment of the 'auditory fovea', i.e. the extensive spatial representation of a narrow band of behaviorally relevant frequencies in the ventromedial part of the IC. In the 5th postnatal week the auditory fovea is concerned with frequencies from 100-118 kHz (Fig. 4c, d). During subsequent development, the frequency tuning of the auditory fovea increases by 20-25 kHz and finally attains the adult range of ca. 125-140 kHz. During this process, neither the bandwidth of the auditory fovea (15-20 kHz) nor the absolute sensitivity of its units (ca. 50 dB SPL) were changed. Further maturation occurred at the single unit level: the sharpness of frequency tuning increased from the 5th to the 7th postnatal weeks (Q-10-dB-values up to 30-60), and upper thresholds emerged (Figs. 4f, 5f). Although in the adult the frequency of the auditory fovea matches that of the vocalised pulses, none of the juvenile bats tested from the 5th to the 7th weeks showed such a frequency match between vocalisation and audition (Figs. 4e, 5e). The results show that postnatal maturation of audition in hipposiderid bats cannot be described by a model based on a single developmental parameter.

Acoustic Stimulation↗
PubMed1987

Coding of sinusoidally amplitude modulated acoustic stimuli in the inferior colliculus of the rufous horseshoe bat, Rhinolophus rouxi.

Single neuron responses to sinusoidally amplitude modulated (SAM) signals were studied in the inferior colliculus of the horseshoe bat, Rhinolophus rouxi. 57% of the neurons responded to SAM stimuli with periodical discharges synchronized to the modulation cycle. The proportion of cells driven by amplitude modulated signals was independent of the best frequency of the neurons. Best modulation frequencies were at or below 100 Hz in about 70% of the neurons. Synchronized activity could be elicited by modulation frequencies up to 400 Hz. Best SAM responses were observed at stimulus intensities 10 dB above threshold. Generally the BMF of a neuron did not change with intensity. The BMF decreased with decreasing modulation depth of the amplitude modulation. A trend for a topographical organization of neurons according to best modulation frequencies was detected. The results did not reveal any significant specialization of the bat's auditory system for coding of amplitude modulations as compared to other mammals.

Animals↗
PubMed1989

Frequency sensitivity and directional hearing in the gleaning bat, Plecotus auritus (Linnaeus 1758).

1. The neural audiogram of the common long-eared bat, Plecotus auritus was recorded from the inferior colliculus (IC). The most sensitive best frequency (BF) thresholds for single neurones are below 0 dB SPL between 7-20 kHz, reaching a best value of -20 dB SPL between 12-20 kHz. The lower and upper limits of hearing occur at 3 kHz and 63 kHz, respectively, based on BF thresholds at 80 dB SPL. BF threshold sensitivities are about 10 dB SPL between 25-50 kHz, corresponding to the energy band of the sonar pulse (26-78 kHz). The tonotopic organization of the central nucleus of the IC (ICC) reveals that neurones with BFs below 20 kHz are disproportionately represented, occupying about 30% of ICC volume, occurring in the more rostral and lateral regions of the nucleus. 2. The acoustical gain of the external ear reaches a peak of about 20 dB between 8-20 kHz. The gain of the pinna increases rapidly above 4 kHz, to a peak of about 15 dB at 7-12 kHz. The pinna gain curve is similar to that of a simple, finite length acoustic horn; expected horn gain is calculated from the average dimensions of the pinna. 3. The directional properties of the external ear are based on sound diffraction by the pinna mouth, which, to a first approximation, is equivalent to an elliptical opening due to the elongated shape of the pinna. The spatial receptive field properties for IC neurones are related to the directional properties of the pinna. The position of the acoustic axis of the pinna and the best position (BP) of spatial receptive fields are both about 25 degrees from the midline between 8-30 kHz but approach the midline to 8 degrees at 45 kHz. In elevation, the acoustic axis and the BP of receptive fields move upwards by 20 degrees between 9-25 kHz, remaining stationary for frequencies up to 60 kHz. 4. The extremely high auditory sensitivity shown by the audiogram and the directionality of hearing are discussed in terms of the adaptation of the auditory system to low frequencies and the role of a large pinna in P. auritus. The functional significance of low frequency hearing in P. auritus is discussed in relation to hunting for prey by listening and is compared to other gleaning species.

Acoustic Stimulation↗
PubMed1986

On the mechanisms of call coding through auditory neurons in the squirrel monkey.

The main goal of the study was to investigate the neural processing of those acoustic signals through auditory neurons whose relevance for communication is either obvious or has been tested by psychoacoustic or behavioral experiments. Thus the activity of cortical, thalamic (MGB) and midbrain (IC) neurons of the auditory pathway were studied with periodically amplitude-modulated (AM) sounds, species-specific AM vocalizations and self-produced vocalizations. With regard to the processing of AM stimuli, there is evidence of a neural correlate to the psychoacoustic phenomenon "fluctuation strength": maximum of the Best Modulation Frequency (BMF) for the cortex was registered at 4 Hz. Furthermore, a relatively large number of units within the IC and the MGB can encode such amplitude changes which have been shown to be of communicative function; here too a neural correlate to the encoding processes of species-specific calls was indicated. Self-produced vocalizations do not seem to underlie a specific processing except that in higher auditory structures, they evoke quantitatively lower responses. In the midbrain, such less active areas are rare and were localized in regions belonging more to secondary auditory structures than primary ones.

Animals↗
PubMed1980

[The origin of the afferent innervation to the inferior colliculus in guinea pig. A horseradish peroxidase study (author's transl)].

The innervation of the inferior colliculus in guinea pig was studied using the method of retrograde axonal transport of horseradish peroxidase (HRP). Following injections of HRP into the central nucleus of the inferior colliculus (IC) HRP labeled cells were found in all auditory nuclei as well as in the temporal cortex. Virtually all neurons of the ventral nucleus of the lateral lemniscus and the medial superior olivary nucleus ipsilateral to the injection side appear to project to the IC. A large number of labeled cells exhibited in the dorsal nucleus of the lateral lemniscus and in the ventral and dorsal cochlear nuclei contralaterally. The lateral superior olivary nucleus was evenly labeled bilaterally while among the periolivary nuclei the dorsomedial periolivary nucleus was heavily labeled ipsilateral to the injection side. Furthermore, labeled neurons occurred in the contralateral IC and in the ventral part of the medial geniculate body on both sides. The pyramidal cells of layer V of the temporal cortex were heavily labeled ipsilaterally.

Animals↗
PubMed1981

[The auditory pathway in guinea pigs. A [14C]2-deoxyglucose study (author's transl)].

The auditory pathway of guinea pigs was labeled with [14C]-deoxyglucose after mon- or binaural stimulation with farfield white noise in a sound-proof chamber. In the autoradiographs, all auditory nuclei were labeled. The highest metabolic effects were seen in the dorsal cochlear nucleus, the lateral superior olivary nucleus, and in the inferior colliculus. No selective labeling was observed in the auditory cortex. Monaural stimulation depressed the metabolic activity contralaterally in the ventral cochlear nucleus and ipsilaterally in the medial nucleus of the trapezoid body, the dorsomedial periolivary nucleus, and in the inferior colliculus.

Acoustic Stimulation↗