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PubMed2007

Protein kinases regulate glycine receptor binding in brain stem auditory nuclei after unilateral cochlear ablation.

Glycinergic synaptic inhibition is part of acoustic information processing in brain stem auditory pathways and contributes to the regulation of neuronal excitation. We found previously that unilateral cochlear ablation (UCA) in young adult guinea pigs decreased [3H]strychnine binding activity in several brain stem auditory nuclei. This study determined if the UCA-induced deficit could be regulated by protein kinase C (PKC), protein kinase A (PKA) or Ca2+/calmodulin-dependent protein kinase II (CaMKII). The specific binding of [3H]strychnine was measured in slices of the dorsal (DCN), posteroventral (PVCN) and anteroventral (AVCN) cochlear nucleus (CN), the lateral (LSO) and medial (MSO) superior olive, and the inferior colliculus (IC) 145 days after UCA. Tissues from age-matched unlesioned animals served as controls. UCA induced deficits in specific binding in the AVCN, PVCN, and LSO on the ablated side and in the MSO bilaterally. These deficits were reversed by 3 microM phorbol 1,2-dibutyrate, a PKC activator, or 0.2 mM dibutyryl-cAMP, a PKA activator. However, 50 nM Ro31-8220, a PKC inhibitor, and 2 microM H-89, a PKA inhibitor, had no effect in unlesioned controls and after UCA. In contrast, 4 microM KN-93, a CaMKII inhibitor, relieved or reversed the UCA-induced binding deficits and elevated binding in the IC. These findings suggest that a UCA-induced down-regulation of glycine receptor synthesis may have occurred via reduced phosphorylation of proteins that control receptor synthesis; this effect was reversed by diminishing CaMKII activity or increasing PKC and PKA activity.

Animals↗
PubMed1999

Penetrating injury to the brainstem after a nailgun accident: a case study.

Nonfatal penetrating injuries to the brainstem offer a unique opportunity to assess subcortical auditory pathway function. A case study of a patient suffering a severe nailgun accident is presented. Hearing sensitivity and acoustic reflexes were normal bilaterally, but word recognition was reduced for one ear. Auditory brainstem response results indicated waves I-IV were present bilaterally, but wave V was absent bilaterally. Results of vestibular findings indicated central pathology also. Results of audiologic, vestibular, radiologic, neurologic, and physical medicine examinations are discussed.

Adult↗
PubMed2003

Mild carbon monoxide exposure and auditory function in the developing rat.

We have examined the influence of chronic mild exposure to carbon monoxide (CO) on cognitive (learning) and auditory function in the developing rat. We have demonstrated that the auditory pathway is compromised at exposures less than 50 ppm, whereas learning was not influenced at 100 ppm. Artificially reared rat pups were exposed to CO during the brain growth spurt and onset of myelination. Spatial learning was assessed using the Morris Water Maze and three tests of auditory function: (1) auditory brainstem conduction times; (2) the amplitude of the eighth nerve's action potential; and (3) otoacoustic emissions carried out on rat pups (age 22- 24 days). The pups were gastrostomy-reared on a rat milk substitute and chronically exposed to CO at discrete concentrations in the range of 12-100 ppm from 6 days of age to post-weaning at 21-23 days of age. We found no difference in auditory brainstem conduction times at all CO concentrations in comparison to non-exposed controls. There was a difference in otoacoustic emissions for test and controls at CO concentrations of 50 ppm but not at lower concentrations. There was a consistent attenuation of the amplitude of the eighth nerve's action potential, even at the lowest CO exposure examined. The attenuation of the amplitude of the action potential of the eighth nerve at 50 ppm carbon monoxide exposure did not completely recover by 73 days of age. We conclude that prolonged mild exposure to carbon monoxide during development causes measurable functional changes at the level of the eighth cranial nerve.

Acoustic Stimulation↗
PubMed1983

Interpretation of brainstem auditory evoked potentials: results from intracranial recordings in humans.

The results of recording intracranially from the auditory nerve, lower brainstem nuclei, and the inferior colliculus in more than 40 patients operated upon for hemifacial spasm and trigeminal neuralgia are presented. Recordings from the auditory nerve have shown that the auditory nerve is the neural generator of the first two peaks in the human ABR. Recordings from the entrance of the eighth nerve into the brainstem and locations close to that reveal potentials; the latencies of the peaks in these potentials match those of peaks III and IV. These peaks are therefore assumed to have their source in second-and third-order neurons of the ascending auditory pathway. Recordings from the inferior colliculus show a surface-positive deflection followed by a slow negative wave usually with several undulations. The latency of the positive peak matches that of wave V of the scalp-recorded ABR. It is assumed that the neural generator of this component of the potential recorded from the inferior colliculus is the lateral lemniscus and that the slow, surface-negative potential originates in the inferior colliculus. The latency of this slow potential is too long to explain that nucleus as the neural generator of peak V, as was assumed previously.

Auditory Pathways↗
PubMed1990

Auditory ear extinction in lacunar syndromes.

A dichotic listening test was administered to 28 patients with lacunar syndromes in order to contribute to the investigation of the subcortical route of interhemispheric auditory pathways. Topographic study showed that lesions in the external capsule or in the anterior limb of the internal capsule in both hemispheres produced left ear extinction. The possibility that some of the auditory fibres travel through the external capsule, as well as the anterior limb of the internal capsule, before crossing the contralateral cerebral lobe is suggested.

Adult↗
PubMed1993

[Effect of myelography on the curve of the auditory evoked early brain stem potentials].

In 50 patients auditory threshold and brain stem evoked potential studies were carried out before and after myelography. Due to the analysis of amplitudes and latencies of auditory brain stem measurements, significant functional disorders of the hearing organ and the auditory pathway could be demonstrated. In most of the patients these functional disorders were found to be subclinical, whereas 12 patients showed alterations extending from a subjectively slight hearing loss to an audiometrically objectified acute hearing loss depending on its intensity in each case. The reasons of these functional disorders could not be clarified. An open cochlear aqueduct through which perilymph enters the subarachnoidal space leading to a secondary endolymphatic hydrops can be considered as the cause in cases where manifest symptoms develop. The changes in brain stem audiometry can be additionally explained by changes in osmolality of the inner ear fluids which may lead to the development of an endolymphatic hydrops.

Auditory Pathways↗
PubMed2000

Induction of visual orientation modules in auditory cortex.

Modules of neurons sharing a common property are a basic organizational feature of mammalian sensory cortex. Primary visual cortex (V1) is characterized by orientation modules--groups of cells that share a preferred stimulus orientation--which are organized into a highly ordered orientation map. Here we show that in ferrets in which retinal projections are routed into the auditory pathway, visually responsive neurons in 'rewired' primary auditory cortex are also organized into orientation modules. The orientation tuning of neurons within these modules is comparable to the tuning of cells in V1 but the orientation map is less orderly. Horizontal connections in rewired cortex are more patchy and periodic than connections in normal auditory cortex, but less so than connections in V1. These data show that afferent activity has a profound influence on diverse components of cortical circuitry, including thalamocortical and local intracortical connections, which are involved in the generation of orientation tuning, and long-range horizontal connections, which are important in creating an orientation map.

Animals↗
PubMed1980

Vector analysis of auditory brain stem responses (BSR) in human beings.

The purpose of the present study is to clarify the origins of BSRs. We recorded BSR by three ortho-diagonal leads (X-axis: right ear canal to left ear canal, Y-axis: vertex to submental position, Z-axis; forehead to inion). We studied the waveforms on each of the three planes: frontal, sagittal, and horizontal and analysed their vectors on the basis of Lissajous'figures. Lissajous'figures revealed the following: (1) The vector of wave I is almost horizontal and is directed towards the non-stimulated side. (2) Wave II seems to be derived from the cochlear nuclei and double firings of the auditory nerves. (3) Wave III represents the activities of the circuits of the auditory pathways in the brain stem. (4) The vector of Wave V is the largest of the five responses, and is directed towards the fronto-parietal region, tilting slightly to the non-stimulated side.

Adolescent↗
PubMed1996

Topography of auditory evoked cortical potentials in children with severe language impairment.

Development of normal speech and language functions is closely related to normal hearing. However, most children with delayed or disturbed speech development show normal tone thresholds and here the investigation has to include higher levels in the auditory system. There is evidence for a connection between language impairment and a central auditory processing disorder, but the underlying mechanisms are not well understood. There is also a need for objective diagnostic methods of central auditory function. In the present study, a computerised method of mapping the scalp topography of long-latency (cortical) auditory evoked potentials (LAEP) was used for assessment of the function in central auditory pathways. Topographic mapping of the LAEP component N1, in adults and normal children, showed reproducible and valid results. In adults, a focal negativity, focus of NI (FNI), with a frontocentral position and contralateral to the stimulated ear was observed. The N1 maps in normal children showed a pattern similar to that in adults, but with some age-related changes. The N1 latencies declined significantly with age in normal children and reached adult values at the ages of 14-16 years. The topography of the LAEP components N1, P2, N2 and the T complex was investigated in 20 children with severe language impairment (LI). The study also included auditory brainstem responses (ABR), electroencephalography (EEG), quantitative EEG (qEEG) and magnetic resonance imaging (MRI). Twenty normal children served as controls (C). A similar topographic pattern was found in the LI and the C children, but with a higher proportion of deviating and non-focal maps in the LI group. The latencies of all components were significantly longer in the LI than in the C children. The diagnostic value of LAEP topography, latency and amplitude was estimated with a scoring system, whereby significantly higher scores were found in the LI group than in the C group. With all three parameters together the sensitivity was 65%, with a specificity of 90%. There was a high degree of pathological EEGs in the LI group. ABR abnormalities were seen in some LI subjects. MRI was normal in all but two LI children. There was no significant correlation between the results of EEG, ABR, MRI and the total score of LAEP, but some LI children showed a wide pathological pattern. In 17 of the 20 LI subjects a pathological result was obtained in one or more of the investigations. In conclusion, our results may indicate that language impairment has a dual pathophysiology, a specific auditory disorder (LAEP, ABR) and a non-specific general cerebral disturbance (EEG, MRI). The highly varying results among the present LI children, with specific and/or non-specific deviations, may be due to heterogeneity of the group with different aetiologies of their language impairment, or to a general developmental disturbance with a varying distribution and penetrance. The scoring system of LAEP proved to be the most sensitive method in separating the LI children from the controls. This may be a promising model for individual diagnostic criteria and for classification of language impairment.

Adolescent↗
PubMed1992

Giant neurons in the caudal pontine reticular formation receive short latency acoustic input: an intracellular recording and HRP-study in the rat.

The reticular formation is composed of heterogeneous cell populations with multiple functions. Among these multiple functions is the processing of sensory information in the context of behavior. The purpose of the present study was to identify and characterize neurons in the reticular formation of the rat that receive auditory input. In order to do so, we combined intracellular electrophysiology in vivo with intracellular injection of horseradish peroxidase, enabling us to correlate electrophysiology unequivocally with anatomy at the single cell level. We found that many neurons in the caudal pontine reticular nucleus (PnC), which we analyzed intracellularly, responded to acoustic stimuli and were excited at short latency (mean EPSP latency: 2.6 ms; mean spike latency: 5.2 ms). This short latency suggests a direct input from the cochlear nucleus, the first central nucleus of the auditory pathway. The morphology revealed that the acoustically driven PnC neurons have very large somata (mean diameter: 44.0 microns). They can therefore be referred to as "giant PnC neurons." Complex dendritic arbors extended from these neurons into the reticular formation and thus formed a large membrane surface for the integration of multimodal inputs. Most of the giant PnC neurons sent their axons caudally into the medial longitudinal fasciculus and can therefore be regarded as reticulospinal neurons. The results demonstrate that the giant reticulospinal PnC neurons are in a position to transmit acoustic information very quickly to spinal cord neurons and to receive converging input from other parts of the brain. They are thus good candidates for participation in the mediation and modulation of acoustically elicited behaviors, such as the short latency acoustic startle response.

Acoustic Stimulation↗
PubMed1988

[Pontine deafness--a new disease picture?].

The clinical features of pontine deafness are demonstrated in six patients with typical findings in pure-tone audiogram and speech audiometry, in stapedial reflex recordings, in brainstem-evoked potentials and cortical evoked potentials. The results of positron emission tomography (PET), magnetic response tomography (MRT), electrocochleography and the promontory test are presented. Results of cerebral spinal fluid and antibody titres in the serum are given. Pontine deafness is characterised by an interruption of the central auditory pathway cranial to the olive. This deafness should be differentiated from other forms of sensorineural hearing loss. The pathogenesis of pontine deafness is still unknown. However we should take it into consideration in the diagnosis of sudden unilateral deafness. No medical treatment method is known to date.

Adolescent↗
PubMed1989

Anatomical bases of binaural interaction in auditory brain-stem responses from guinea pig.

There is a non-linear interaction of binaural stimulation on auditory brain-stem potentials in both human and animals. The interaction takes the form of the binaurally evoked ABR being of smaller amplitude than the sum of the monaurally evoked ABRs. In the guinea pig this interaction occurs at the time of components P4, N4 and P5. In order to investigate the generator sites of binaural interaction in the ABR, various lesions were made in the brain-stem auditory system in 29 guinea pigs. The effects of those lesions on binaural interaction were as follows: (1) unilateral lesion of lateral lemniscus or bilateral lesions of the inferior colliculi had no significant effect on binaural interaction; (2) transection of the lateral lemnisci bilaterally was associated with a loss of the component of binaural interaction associated in time with N4; (3) a lesion just lateral to the lateral superior olivary complex resulted in an attenuation of the component of binaural interaction associated in time with P4; (4) complete section of the decussating fibers of the trapezoid body or a complete unilateral lesion of the superior olivary complex led to a loss of all components of binaural interaction. These results suggest that binaural interaction in the guinea pig ABR requires the integrity of several distinct portions of the brain-stem auditory pathway, i.e., both lateral lemnisci are required for the interaction occurring at the time of N4; the brain-stem just lateral to the lateral superior olive participates in the interaction at the time of P4. The trapezoid body and superior olivary nucleus are required for binaural interaction at P4, N4 and P5.

Animals↗
PubMed1997

Neuronal and transneuronal degeneration of auditory axons in the brainstem after cochlear lesions in the chinchilla: cochleotopic and non-cochleotopic patterns.

Terminal axonal degeneration in the brain following cochlear lesions was studied with the Nauta-Rasmussen method. Losses of hair cells and myelinated cochlear fibers were assessed. The cochleotopic map projected, from apex to base, on the ventral-to-dorsal axes of the cochlear nuclei. The cochleotopic correspondence was better for loss of cochlear nerve fibers and inner hair cells, than for outer hair cells. Cochlear fibers were traced to all parts of the cochlear nucleus, including the small-cell shell, also to cell-group Y and the flocculus. Terminal axonal degeneration in nuclei of the superior olivary complex, lateral lemniscus, and inferior colliculus was interpreted as transynaptic, since degenerated axons could not be traced to these locations from the cochlear nerve or trapezoid body. Moreover, biotinylated dextran amine injection in the basal turn of scala media of a normal cochlea labeled cochlear nerve fibers projecting to the high-frequency regions of the cochlear nuclei and to the flocculus, but not to more central auditory nuclei. This is the first detailed account of transynaptic degeneration in the ascending auditory pathway resulting from cochlear damage in an adult mammal. These findings are consistent with a dystrophic process depending on hair-cell loss and/or direct damage to cochlear nerve fibers.

Animals↗
PubMed1981

Physiological mechanisms in auditory brainstem-evoked response.

A critical review is presented of the physiological background for the interpretation of ABR auditory brainstem response). The importance of the transformation of the monophasic click stimulus to a dampled oscillation on the basilar membrane, the travelling wave velocity and the synchronization of high frequency units in the auditory nerve are emphasized. The ABR is an expression of the wave front of the leading volley of synchronized action potentials generated in nerve cell bodies in the relay stations of ascending auditory pathway. It is concluded that the physiological evidence for IC as sole, or main generator of wave V is very incomplete. The possibility of multiple generators in the SOC-complex is emphasized.

Acoustic Stimulation↗
PubMed2006

Responses of neurons in the ventral nucleus of the lateral lemniscus to sinusoidally amplitude modulated tones.

Fluctuations in the amplitude of a sound play an important role in our perception of pitch and acoustic space, but their neural analysis has not been fully elucidated. The ventral nucleus of the lateral lemniscus (VNLL) has been implicated in the processing of such temporal features of a sound. This study examines responses of neurons in the VNLL of unanesthetized rabbits to sinusoidally amplitude modulated tones, a type of stimulus that has often been used to investigate encoding of temporal information. Modulation transfer functions of responses were calculated in two ways: based on discharge rates (rMTFs) and on synchronization to the envelope (tMTFs). Among the variety of rMTFs, two types were readily identifiable: flat and band-pass. The responses of neurons exhibiting these types of rMTF differed in several ways. Neurons with flat rMTFs typically had moderate rates of spontaneous activity, sustained responses to short tone bursts, and low-pass or band-pass tMTFs. Neurons with band-pass rMTFs typically had low spontaneous activity, onset responses to short tone bursts, and flat tMTFs. The vast majority synchronized strongly to the modulation envelope. The best modulation frequencies of neurons with band-pass rMTFs extended from 14 to 283 Hz. The presence of neurons with band-pass rMTFs in the VNLL suggests that this nucleus plays a role in converting the temporal code for modulation frequency used in lower structures into a rate-based code for use higher in the auditory pathway. The substantial number of neurons with more complex modulation transfer functions indicates that the VNLL has other functions.

Acoustic Stimulation↗
PubMedDate not supplied

Hearing loss of a central type secondary to carbon monoxide poisoning.

The effect of carbon monoxide poisoning on the threshold sensitivity of the responses from the auditory cortex, inferior colliculus, and cochlea to acoustic stimuli in guinea pigs was studied. The toxicity of carbon monoxide is believed to be secondary to tissue hypoxia and is partially reversible. Loss of auditory threshold sensitivity in carbon monoxide poisoning is most prominent at the auditory cortex. The loss of sensitivity at the inferior colliculus is the next most severe. There is no loss of sensitivity at the cochlea. The relative vulnerability of the central auditory pathway to carbon monoxide poisoning as compared with the end organ is demonstrated.

Animals↗
PubMed1989

Correlations between various measures of head size and auditory brainstem response latencies.

The literature is mixed concerning the degree to which between-subject variance in the latencies of the auditory brainstem response (ABR) relates to differences in the length of the auditory pathway. Most investigations have used one of several measures of head size to indirectly index brain size and neural pathway length. While some studies have found a positive correlation between head size and the latencies of the ABR, others have reported little or no relationship. We hypothesized that the differences between studies result from differences in the head dimensions measured, the precision of measurement technique, and issues of sampling. We therefore decided to use the International 10-20 system of electrode placement to provide reproducible skull benchmarks on which to base head size measures, to obtain measures of head size via two procedures, and to control external variables that might influence the ABR. The results show that head size has a moderate positive influence on the latencies of the ABR given precise head size measures.

Adult↗