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PubMed1984

Functional activation in the auditory system of the rat produced by arousing reticular stimulation: a 2-deoxyglucose study.

The 2-deoxyglucose (2-DG) autoradiographic method was used to map the activity in the auditory pathway during behaviorally arousing electrical stimulation of the mesencephalic reticular formation (RET). Uptake of 2-DG during RET stimulation was compared to the effect of a frequency-modulated tone (4-5 kHz, 60 dB SPL) and to controls without stimulation. The major finding was a specific pattern of increased metabolic activation throughout the auditory pathway evoked during RET stimulation. The observed increases in 2-DG uptake were always greater in RET-stimulated rats as compared to sound-stimulated or control rats. The dorsal cochlear nucleus (DCN) showed the largest incorporation of 2-DG among the auditory nuclei of the brainstem in RET-stimulated rats. In the central nucleus of the inferior colliculus a layered pattern made of 3 discrete bands of high 2-DG uptake was visible in RET-stimulated rats. The medial geniculate (MG) and the auditory cortex (AC) also showed highly significant increases in 2-DG uptake induced by RET stimulation. The method provided correlations between classical morphological schemes of parcellation on nuclei and functionally defined areas of increased 2-DG uptake. Our observations represent the first anatomical demonstration of the activating effects of RET stimulation in a sensory system, and they support the concepts of arousing reticular mechanisms for sensory control.

Animals↗
PubMed1988

Influence of envelope rise time on neural responses in the auditory system of anurans.

The influence of envelope rise time on neural responses was investigated in the central auditory pathway of frogs. Single unit and evoked potential recordings were made from the dorsal medullary nucleus (DMN) and thalamus, respectively. It was found that phasic neurons (15% of the population) in the DMN responded preferentially to stimuli with rapid (less than 25 ms) rise times. Acoustically evoked potentials (AEPs) recorded from the thalamus, specifically the Nucleus of Bellonci, also showed more pronounced responses to stimuli with rapid, rather than slower, envelope rise times. Interestingly, the leopard frog mating call, which has a rapid onset, elicited strong neuronal discharge both within the DMN and thalamus. In contrast, the mating call of bullfrogs, a species sympatric with leopard frogs, has a characteristically slow (greater than 100 ms) envelope rise time and elicited little, if any, response. These findings indicate the presence of neural specializations within the frog's auditory pathway for the optimal detection of the conspecific mating call. The relevance of these findings for stimulus coding in the auditory pathway of other vertebrates is discussed.

Animals↗
PubMed1985

Patterns of organization in auditory cortex.

Previous work has described recently developed techniques that are contributing to advances in the study of the auditory system; some of these techniques have been used to make significant progress in this field. This paper includes a discussion of the tonotopic and binaural organizations of the auditory cortex (especially area AI), the neuronal connections between auditory cortical fields, the relationships between the functional maps and the connectivity patterns, the nature of binaural processing within AI, and the techniques used to assess the structural and functional properties of this portion of the central auditory pathway.

Animals↗
PubMed1997

Histological and physiological effects of the central auditory prosthesis: surface versus penetrating electrodes.

To rehabilitate profoundly deaf patients who are not suitable for cochlear implants, central auditory prostheses have been implanted. To compare two possible electrode configurations - penetrating and surface ones - electrical stimulation of the cochlear nucleus with both types of arrays was tested on guinea pigs and cats. Electrophysiological, autoradiographic and histological measures were used to study effects of the central auditory prostheses on the auditory pathway. The results showed that a successful electrically evoked auditory brainstem response could be recorded with both surface and penetrating electrodes in cats and guinea pigs. In guinea pigs the penetrating electrodes had advantages over surface arrays in the sense of lower thresholds and wider dynamic ranges. In cats penetrating electrodes showed lower thresholds than surface ones. In cats and guinea pigs stimulated with either surface or penetrating electrodes, evoked 2-deoxyglucose (2-DG) label was found in the auditory pathway from the cochlear nucleus to the inferior colliculus. No non-auditory tissues were found with evoked 2-DG label. Histological results showed that in subdivisions of the guinea pig cochlear nucleus stimulated with penetrating electrodes the neurone density was decreased, and the mean soma area was increased compared with the control side. In the cat, penetrating electrodes were associated only with increased mean soma area in parts of the stimulated cochlear nucleus. These results suggest that the physiological advantages of penetrating electrodes over surface ones were achieved with some trade-off in safety, especially in the guinea pig.

Animals↗
PubMed1980

Age-related changes in the auditory evoked brainstem potentials of albino and pigmented guinea pigs.

The auditory evoked brainstem responses of guniea pigs in two age groups were recorded and examined for evidence of age-dependent changes at peripheral stations in the auditory pathway. Because pigmented guinea pigs have been found to be less sensitive to sounds than albinos, both groups were included in this study. Old and young animals did not differ in response latency or in the conduction times associated with the individual potentials. By contrast, the amplitudes of the brainstem responses to high-frequency stimuli were distinctly reduced in old guinea pigs, with no difference in the dynamic of the amplitude between the two age groups. Within each age group, albino and pigmented animals resembled one another in all parameters studied. The effect of the aging process at the peripheral stations of the auditory pathway is discussed in the light of these results.

Aging↗
PubMed2002

A sensitive period for the development of the central auditory system in children with cochlear implants: implications for age of implantation.

OBJECTIVE: The aim of the present experiment was to assess the consequences of cochlear implantation at different ages on the development of the human central auditory system. DESIGN: Our measure of the maturity of central auditory pathways was the latency of the P1 cortical auditory evoked potential. Because P1 latencies vary as a function of chronological age, they can be used to infer the maturational status of auditory pathways in congenitally deafened children who regain hearing after being fit with a cochlear implant. We examined the development of P1 response latencies in 104 congenitally deaf children who had been fit with cochlear implants at ages ranging from 1.3 yr to 17.5 yr and three congenitally deaf adults. The independent variable was the duration of deafness before cochlear implantation. The dependent variable was the latency of the P1 cortical auditory evoked potential. RESULTS: A comparison of P1 latencies in implanted children with those of age-matched normal-hearing peers revealed that implanted children with the longest period of auditory deprivation before implantation-7 or more yr-had abnormal cortical response latencies to speech. Implanted children with the shortest period of auditory deprivation-approximately 3.5 yr or less-evidenced age-appropriate latency responses within 6 mo after the onset of electrical stimulation. CONCLUSIONS: Our data suggest that in the absence of normal stimulation there is a sensitive period of about 3.5 yr during which the human central auditory system remains maximally plastic. Plasticity remains in some, but not all children until approximately age 7. After age 7, plasticity is greatly reduced. These data may be relevant to the issue of when best to place a cochlear implant in a congenitally deaf child.

Adolescent↗
PubMed2003

Putative isotocin distributions in sonic fish: relation to vasotocin and vocal-acoustic circuitry.

Recent neurophysiological evidence in the plainfin midshipman fish (Porichthys notatus) demonstrated that isotocin (IT) and arginine vasotocin (AVT) modulate fictive vocalizations divergently between three reproductive morphs. To provide an anatomical framework for the modulation of vocalization by IT and to foster comparisons with the distributions of the IT homologues mesotocin (MT) and oxytocin (OT) in other vertebrate groups, we describe putative IT distributions in the midshipman and the closely related gulf toadfish, Opsanus beta. Double-label fluorescent histochemistry was used for IT and AVT (by using antibodies for MT, OT, and the mammalian AVT homologue, arginine vasopressin [AVP]). MT/OT-like immunoreactive (MT/OT-lir) cell groups were found in the anterior parvocellular, posterior parvocellular, and magnocellular preoptic nuclei. MT/OT-lir fibers and putative terminals densely innervated the ventral telencephalon and numerous areas in the hypothalamus and brainstem. These distributions included all sites of vocal-acoustic integration recently identified for the forebrain and midbrain and diencephalic components of the ascending auditory pathway. Results were qualitatively comparable across morphs, species, and seasons. In contrast to the widespread distribution of MT/OT-lir, AVP-lir somata, fibers, and putative terminals were almost completely restricted to vocal-acoustic regions. These data parallel previous descriptions of AVT immunoreactivity in these species, although the present methods showed a previously undescribed, seasonally variable AVP-lir cell group in the anterior tuberal hypothalamus, a vocally active site and a component of the ascending auditory pathway. These findings provided anatomic support for the role of IT and AVT in the modulation of vocal behavior at multiple levels of the central vocal-acoustic circuitry.

Animals↗
PubMed1997

The columnar region of the ventral nucleus of the lateral lemniscus in the big brown bat (Eptesicus fuscus): synaptic arrangements and structural correlates of feedforward inhibitory function.

Neurons of the columnar region of the ventral nucleus of the lateral lemniscus of Eptesicus fuscus respond with high-precision constant-latency responses to sound onsets and possess remarkably broad tuning. To study the synaptic basis for this specialized monaural auditory processing and to elucidate the excitatory or inhibitory nature of the input and output circuitry, we have used classical transmission electron microscopy, and postembedding immunocytochemistry for gamma aminobutyric acid (GABA) and glycine on serial semithin sections. The dominant putatively excitatory perisomatic input is provided by large calyx-like terminals that possess round synaptic vesicles and asymmetric synaptic contacts. Additionally, calyces contact the dendrites of neighboring neurons. Putatively inhibitory small boutons possess pleomorphic or flattened synaptic vesicles and symmetrical contacts and are sparsely distributed on somata and dendrites. Almost all neurons are glycine-immunoreactive. There is a moderate amount of glycine-immunoreactive puncta; GABA-immunoreactive puncta are rare. This suggests that (1) there is a fast robust excitatory synaptic input via calyx-like perisomatic endings, (2) calyx-like endings distribute frequency-specific excitatory input across isofrequency sheets by virtue of parallel synapses to somata and adjacent dendrites, and thus, dendritic integration may contribute to the broadening of frequency tuning, (3) the columnar region forms an inhibitory glycinergic feedforward relay in the ascending auditory pathway, a relay that is probably involved in creating filters for time-varying signals.

Afferent Pathways↗
PubMed1999

Timing in the auditory system of the bat.

Echolocating bats use audition to guide much of their behavior. As in all vertebrates, their lower brainstem contains a number of parallel auditory pathways that provide excitatory or inhibitory outputs differing in their temporal discharge patterns and latencies. These pathways converge in the auditory midbrain, where many neurons are tuned to biologically important parameters of sound, including signal duration, frequency-modulated sweep direction, and the rate of periodic frequency or amplitude modulations. This tuning to biologically relevant temporal patterns of sound is created through the interplay of the time-delayed excitatory and inhibitory inputs to midbrain neurons. Because the tuning process requires integration over a relatively long time period, the rate at which midbrain auditory neurons respond corresponds to the cadence of sounds rather than their fine structure and may provide an output that is closely matched to the rate at which motor systems operate.

Animals↗
PubMed2003

Functional imaging of pitch analysis.

This work addresses the brain basis for the analysis of pitch and pitch patterns required for normal musical perception. Recent functional imaging experiments are consistent with a hierarchical scheme for the analysis of pitch. Mechanisms in the ascending auditory pathway to the primary auditory cortex allow the representation of the spectral and temporal features of individual notes required for the perception of their pitch. Converging experiments where pitch strength is manipulated in different ways suggest that there may be a "pitch center" in the lateral part of Heschl's gyrus, adjacent to the primary auditory area. The suggestion is that there is a representation in this area that correlates with the perception of pitch rather than a simple mapping of physical stimulus characteristics. The analysis of patterns of pitch such as melodies, as opposed to the pitch of individual notes, involves much more distributed processing in the superior temporal lobes and frontal lobes. Involvement of the frontal lobe in pitch pattern analysis may in part reflect whether subjects analyze the pitch patterns in order to carry out an output task.

Auditory Pathways↗
PubMed1986

Connectional basis for frequency representation in the nuclei of the lateral lemniscus of the bat Eptesicus fuscus.

To study the role of the lateral lemniscus as a link in the ascending auditory pathway, injections of neuronal tracers were placed in the anteroventral cochlear nucleus (AVCN) and in the inferior colliculus of the bat Eptesicus fuscus. To correlate the anatomical results with tonotopic organization, the characteristic frequency of cells at each injection site was determined electrophysiologically. Pathways from AVCN diverge to 3 major targets in the lateral lemniscus, the intermediate nucleus and 2 divisions of the ventral nucleus (VNLL). Projections from these 3 nuclei then converge at the inferior colliculus. One cell group is particularly notable for its cytoarchitectural appearance. It is referred to here as the columnar area of VNLL because its cells are organized as a tightly packed matrix of columns and rows. The connections of the columnar area are organized in sheets that are precisely related to the tonotopic organization of both AVCN and the inferior colliculus. Sheets of cells in the dorsal part of the columnar area receive projections from low-frequency parts of AVCN and project to low-frequency parts of the inferior colliculus. These sheets of connections occupy successively more ventral locations as the tonotopic focus of the injection site increases in frequency. The entire range of frequencies audible to the bat is systematically represented along the dorsal-ventral dimension of the columnar area. Because each column is only 20-30 cells in height, frequency representation must be compressed in this dimension. Within the columnar area there is an overrepresentation of frequencies between 25 and 50 kHz, which corresponds roughly to the range of the FM echo-location call in Eptesicus. The connections of the other nuclei of the lateral lemniscus are not as precisely related to the tonotopic organization of the system as are those of the columnar area.

Afferent Pathways↗
PubMed1996

Connections of the torus semicircularis and oliva superior in the frog, Rana esculenta: a Phaseolus vulgaris leucoagglutinin labeling study.

The afferent and efferent connections of the frog principal nucleus (TP) of torus semicircularis (TOS) and superior olive (SO) were examined by employing the anterograde and retrograde transport patterns of Phaseolus vulgaris leucoagglutinin (PHA-L). After injecting the tracer into these nuclei it was found that the TP projected to the ipsilateral posterior and central thalamic nuclei, all subdivisions of the bilateral TDS and the ipsilateral nucleus isthmi (NI). In the rhombencephalon the projection was restricted mainly to the contralateral SO and the cochlear nucleus (CN). Retrogradely labeled cells were found in most of the areas that contained anterogradely labeled terminals. The termination areas of the SO fibers were similar to the projections of fibers of TP origin in the diencephalic and in the mesencephalic auditory centers. A strong projection was followed into the contralateral SO; the CNs received fibers at both sides. Caudally to the SO the reticular formation, the spinal nucleus of the trigeminal nerve, the solitary nucleus and the dorsal column nuclei were supplied by the fibers of the SO origin. Retrogradely labeled cells were found in the TOS, tegmental nuclei, solitary nucleus, dorsal column nuclei and in the spinal nucleus of the trigeminal nerve. Our results indicate that the frog auditory pathway is more complex at the level of the secondary and tertiary fiber projections than has been previously recognized.

Afferent Pathways↗
PubMed2001

[Central hyperacusis with phonophobia in multiple sclerosis].

Auditory disturbances are a well known symptom in patients with multiple sclerosis (MS). Uni- or bilateral hypacusis or deafness in patients with normal auditory testing is considered to be a result of lesions in the central auditory pathway. Only rarely described is a central phonophobia whereby acoustic stimuli induce unpleasant and painful perceptions, with consecutive avoidance of these factors. Our first patient described acute shooting pain in the right cheek, triggered only through the ringing of a telephone. The second patient had uncomfortable perception of nonverbal noise. For example the wrinkling of paper bags was unbearable for him. The third patient had difficulties localizing the source of sound and disturbing echos while listening to speech or music. Clinically, in all patients symptoms of a brainstem syndrome were found, whereas auditory testing including inspection, audiometry, and stapedius reflex was normal. We found pathological acoustic evoked potentials (AEP) in all three patients with a prolonged latency III-V and T2 lesions in the ipsilateral pons and central auditory pathway. In case one, we suppose a lateral spread between the lateral lemniscus and the central trigeminal pathway. In the other cases, a dysfunction of the central sensory modulation which controls the regulation of sensitivity of incoming acoustic stimuli seems to be the cause of hyperacusis. All our patients developed clinically confirmed MS in the further course after suffering from phonophobia as their first symptom.

Acoustic Stimulation↗
PubMed1979

Bilaterally recorded brain stem auditory evoked responses. Their asymmetric abnormalities and lesions of the brain stem.

Simultaneous bilateral recordings (C3 to A1 and C4 to A2) of brain stem auditory evoked responses have been studied in 67 supratentorial lesions, nine midbrain lesions, 21 intrinsic pontine lesions, and 23 extrinsic compressions of the pons. The responses in supratentorial lesions showed completely normal records. In midbrain lesions, wave V was specifically altered. As wave 1 has been shown to be a far-field seventh nerve potential, and wave V the midbrain potential, waves II to IV can be inferred to originate in the central auditory pathway between the seventh nerve and the midbrain. Alterations of waves II to IV correlated well with localization of pontine lesions, and asymmetric alterations of the bilaterally recorded responses were associated with unilateral lesions of the brain stem auditory pathway and/or lesions of the crossed auditory projections.

Acoustic Stimulation↗
PubMed2004

Central auditory maturation and babbling development in infants with cochlear implants.

OBJECTIVE: To examine the relationship between the maturation of central auditory pathways and the development of canonical (speechlike) babbling in infants with cochlear implants. DESIGN: Comparison of the latencies of the P1 cortical auditory evoked potential and vocalizations produced by subjects before they were fitted with a cochlear implant and at several time points within the first year after implantation. SUBJECTS: Two congenitally deaf children who were implanted with a multichannel cochlear implant at ages 13 and 14 months. INTERVENTIONS: P1 response latencies were recorded in response to a /ba/ stimulus before implantation and at several time points following implantation. Vocalizations produced by the subjects while interacting with their caregiver were audiorecorded twice before implantation and at monthly sessions following implantation. RESULTS: Subjects showed a rapid decrease in P1 latencies resulting in normal P1 latencies within about 3 months after implantation. Before implantation, the vocalizations were primarily of a precanonical nature. After 3 months' experience with the implants, the proportion of canonical vocalizations increased dramatically relative to the number of precanonical utterances. CONCLUSIONS: Results of this study suggest that the development of P1 response latencies and the development of early communicative behaviors may follow a similar developmental trajectory in children implanted early. Although preliminary, these findings indicate that the development of early communicative behaviors following implantation may be positively influenced by the rate of plastic changes in central auditory pathways.

Auditory Pathways↗
PubMed2005

A prospective randomized controlled trial evaluating alcohol on loudness perception in cochlear implant users.

AIM: The aim of this study was to determine the effects of alcohol on the psychophysical responses in patients with cochlear implants. This has not been previously studied. It was also hoped to provide information that could suggest possible sites of action of the known effects of alcohol on the auditory pathway. DESIGN: A prospective randomized placebo-controlled trial, with full ethical approval. PARTICIPANTS: Eight successful cochlear implant users were selected, of whom two had bilateral implants which were tested separately. In total 10 cochlear implants were tested. INTERVENTION: Alcohol was given in the form of vodka (50% alcohol, 1 mL/kg body weight) with 500 mL of orange and cranberry juice. The placebo control was given in the form of 500 mL of orange and cranberry juice alone. OUTCOME MEASUREMENT: The 'comfort level' (C level) was recorded before, and 1 h after alcohol or placebo ingestion for each patient's cochlear implant. Blood alcohol concentration was determined prior to alcohol or placebo consumption and then repeated after 45, 60, 90 and 180 min. RESULTS: The mean blood alcohol concentration 1 h after ingestion was 50 mg/dL. In the 'alcohol' arm the mean electrical unit increase in the C level was 19.9 with a standard deviation of 2.2. In the control arm the mean change in C level was 0.10 with a standard deviation of 0.3. CONCLUSIONS: In this first prospective randomized control study of the effect of alcohol on sound perception in cochlear implant users, alcohol significantly increased the upper end of the dynamic range (C levels) in comparison with placebo (P = <0.0001 using paired t-test analysis). This effect is likely to be the result of change in the auditory pathways proximal to the cochlea.

Adult↗
PubMed2004

Optical mapping of neural responses and their gamma-aminobutyric acid-ergic inhibitory effects in the auditory brainstem of early postnatal mice.

gamma-Aminobutyric acid (GABA)ergic neurons play important tropic and modulatory roles in the auditory pathway, especially in the early stage between postnatal Days 0 and 5. The effects of GABA and GABAa receptor antagonist were observed in this experimental study. Numerous histological and electrophysiological studies have been performed on the contribution of GABA to the auditory pathway; however, the spatio-temporal patterns of excitatory propagation and the relationships between GABA receptor and excitatory propagation have yet to be reported. Using an optical recording technique and a voltage-sensitive dye, the spatio-temporal patterns of excitatory propagation were observed in the auditory brainstem slices of early postnatal mice. A bath containing 50 microM GABA was applied, which largely inhibited the excitatory activities along the vestibulocochlear pathway. Bicuculline methiodide (BMI), a competitive antagonist against GABAa receptor, partially reversed the effects of GABA on the optical signals. Bath application of BMI alone helped to facilitate the depolarization course and its effect was apparent as an enlargement of the depolarized region from the cochlear nucleus and vestibular nucleus to some adjacent brainstem nuclei, as well as enhancing the amplitude of changes in the optical signals. The experimental results seem to suggest that GABAa receptors are widely distributed in an early postnatal auditory brainstem. GABA exhibited a greater modulating effect in the adjacent brainstem nuclei, which are involved in complex information processes, than that observed in the modulating primary auditory pathway. In the present experiment, significant GABAergic contributions to the optical recordings in the auditory brainstem were observed.

Animals↗
PubMedDate not supplied

Binaural stimulation reveals functional differences between midline and temporal components of the middle latency response in guinea pigs.

Two morphologically distinct auditory middle latency response (MLR) wave forms can be recorded from the surface of the guinea pig brain. The temporal response is recorded from the temporal lobe contralateral to the stimulus ear, and the midline response is recorded over the posterior midline. Experimental evidence suggests that different neural generators contribute to the two responses. Furthermore, it appears that the temporal response principally reflects activity of the primary auditory pathway while the midline response reflects non-primary pathways. Although it is known that neurons throughout the auditory pathway exhibit distinct binaural interaction (BI) properties, thus far there have been no systematic attempts to differentiate the MLR wave forms in response to binaural stimulation. The purpose of this study was to determine if binaural click stimulation could functionally differentiate the midline and temporal MLR responses in the guinea pig. Binaural click stimulation caused a significant decrease in temporal MLR peak amplitudes, and a significant increase in midline MLR amplitudes. The fact that different BI patterns were observed suggests that the two MLR components are functionally distinct. The data further support the hypothesis that the midline and temporal MLR in guinea pigs reflect different neural generators and pathways.

Acoustic Stimulation↗