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PubMed2000

Coil design for real and sham transcranial magnetic stimulation.

Transcranial magnetic stimulation (TMS) can be used to excite the human cortex noninvasively. TMS also activates scalp muscles and sensory receptors; additionally, the loud sound from the stimulating coil activates auditory pathways. These side effects complicate the interpretation of the results of TMS studies. For control experiments, we have designed a coil that can produce both real and sham stimulation without moving the coil. The sham TMS is similar to the real TMS, except for the different relative direction of the currents in the two loops of the figure-of-eight coil. While the real TMS elicited activation of hand muscles, sham TMS had no such effect; however, the auditory-evoked potentials were similar.

Electroencephalography↗
PubMed1992

The effect of olivocochlear bundle transection on tuning curves and acoustic distortion products.

A growing body of research suggests that the efferent innervation to the cochlea, the olivocochlear bundle (OCB), may modulate the mechanical function of the cochlea. However, the role of tonic OCB input in cochlear function remains poorly understood. The purpose of this study was to determine the influence of tonic efferent input on cochlear mechanics, by transecting the entire OCB in guinea pigs, and observing changes in tuning curves and acoustic distortion products. The OCB was transected by avulsing the inferior vestibular nerve as it enters the internal auditory canal of the right bulla. Auditory brainstem response (ABR) thresholds, ABR tuning curves, and acoustic distortion products were measured before and after surgery. Successful transection of the OCB was verified histochemically. Results revealed no consistent changes in tuning curves or in the growth functions of the distortion products. To the extent that these measures reflect cochlear mechanical nonlinearities, it is concluded that tonic OCB input is not necessary for grossly normal cochlear mechanical function in the 10-kHz region of the guinea pig cochlea. It thus seems unlikely that the efferents are involved in establishing a "set point" for cochlear operation.

Animals↗
PubMed2001

"What" and "where" in the human auditory system.

The extent to which sound identification and sound localization depend on specialized auditory pathways was examined by using functional magnetic resonance imaging and event-related brain potentials. Participants performed an S1-S2 match-to-sample task in which S1 differed from S2 in its pitch and/or location. In the pitch task, participants indicated whether S2 was lower, identical, or higher in pitch than S1. In the location task, participants were asked to localize S2 relative to S1 (i.e., leftward, same, or rightward). Relative to location, pitch processing generated greater activation in auditory cortex and the inferior frontal gyrus. Conversely, identifying the location of S2 relative to S1 generated greater activation in posterior temporal cortex, parietal cortex, and the superior frontal sulcus. Differential task-related effects on event-related brain potentials (ERPs) were seen in anterior and posterior brain regions beginning at 300 ms poststimulus and lasting for several hundred milliseconds. The converging evidence from two independent measurements of dissociable brain activity during identification and localization of identical stimuli provides strong support for specialized auditory streams in the human brain. These findings are analogous to the "what" and "where" segregation of visual information processing, and suggest that a similar functional organization exists for processing information from the auditory modality.

Acoustic Stimulation↗
PubMed1996

Slowing of central conduction in X-linked Charcot-Marie-Tooth neuropathy shown by brain stem auditory evoked responses.

BACKGROUND: The most common form of CMT with slow nerve conduction velocities (CMT type I) is CMT1A, caused by a submicroscopic duplication of a region of DNA on chromosome 17 including the PMP22 gene. This gene is expressed in peripheral nerve but not in the CNS. The second most common form is CMTX, caused by mutations in the connexin32 gene in the X chromosome. Connexin32 is expressed both in brain and in peripheral nerve. These molecular variants are difficult to distinguish clinically. METHODS: Brain stem auditory evoked responses (BAERs) were measured in patients with CTMX and CMT1A. RESULTS: BAERs showed central conduction slowing in male patients with CMTX which did not overlap the normal range. Patients with CMT1A had a delay in wave I latency but otherwise normal responses. These results are consistent with the pattern of expression of PMP22 in the peripheral portion of the eighth nerve (myelinated by Schwann cells) and of connexin32 in the central portion in the brainstem auditory pathways (myelinated by oligodendrocytes). This is the first evidence for central involvement in CMTX. CONCLUSION: BAERs are useful to distinguish CMTX from CMT1A and may assist selection of appropriate patients for connexin32 mutation analysis.

Adolescent↗
PubMed1999

[Auditory brain stem response and child attention deficit hyperactivity disorder].

Diagnostic audiological test performed in two children showed remarkable differences between the results of behavioral audiometry and those of auditory evoked response audiometry. The results of neuropsychological evaluation showed attention disorders. It is possible that a response desynchronisation in the auditory pathway may exist in these disorders. Interpretation of ABR findings can be problematic in children with learning disabilities or minimal cerebral dysfunction.

Attention Deficit Disorder with Hyperactivity↗
PubMed1986

Three-channel Lissajous' trajectory of human auditory brain-stem evoked potentials. III. Effects of click rate.

Three-channel Lissajous' trajectories (3-CLT) of the human auditory brain-stem evoked potentials (ABEPs) were recorded from 14 adult subjects using click rates of 10, 55 and 80/sec. The 3-CLTs were analysed and described in terms of their constituent planar segments and their trajectory amplitudes at each stimulus rate. Increasing stimulus rate resulted in an increase of planar segment duration which was more pronounced for segments 'a' and 'e', an increase in apex latency which was more pronounced the later the component and a decrease in planar segment size and peak trajectory amplitude which was more pronounced the earlier the component. These findings support the involvement of synaptic efficacy changes in the effects of stimulus rate on ABEP. The results are explained by overlapping convergence and divergence in the ascending auditory pathway. These results support the notion that the principal generator of each component is activated by the principal generator of the previous component, with some temporal overlap of their activities. Such temporal overlap may be minimized by using low intensity high rate stimuli.

Brain Stem↗
PubMed1979

Selective adaptation to frequency-modulated tones: evidence for an information-processing channel selectively sensitive to frequency changes.

Exposure to an FM tone elevates FM threshold but not AM threshold. This holds for a wide range of frequency deviations (delta F = +/- 0.4 Hz- +/- 30 Hz at least) provided that modulation frequency is low (fm = 2 Hz), but if fm is somewhat higher (e.g., 8 Hz) the finding only holds for small frequency deviations. FM threshold can rise with time up to an adapting duration of at least 1200 s, through this buildup depends on frequency deviation. Exposure to an AM tone elevates AM threshold, but not FM threshold, over a wide range of modulation depths (at least m = 5%--50%). Quasi-FM (QFM) adapting tones resemble FM adapting tones in their effects upon FM and AM sensitivities, even though QFM and AM adapting tones have identical power spectra. Exposure to a pure tone produces no difference between FM and AM threshold elevations. These data can be explained if the human auditory pathway contains separate information-processing channels for AM and FM signals whose sensitivities do not overlap even with suprathreshold stimuli. We suppose that the FM channel (but not the AM channel) is sensitive to changing differences (or ratios) between signals from different sites along the basilar membrane.

Adaptation, Psychological↗
PubMed2002

Electrophysiological findings in two bilateral cochlear implant cases: does the duration of deafness affect electrically evoked auditory brain stem responses?

Bilateral cochlear implantation provides an interesting model for in vivo study of the effect of long-term profound deafness on neural transmission. We present electrophysiological observations on 2 patients implanted with the MXM Binaural Digisonic Convex system. This uncommon design consists of 2 electrode arrays placed bilaterally into the scala tympani and controlled by a single speech processor. In both patients, the duration of deafness before cochlear implantation clearly differed from one ear to the other. Electrically evoked auditory brain stem responses (EABRs) were measured and the EABRs from the ear with the longer deafness duration showed a lengthening of wave V latency. In I patient, recordings from this ear also showed a lack of reproducibility of wave III. The data suggest that neural responsiveness in the peripheral and intermediate auditory pathways is adversely affected by deafness duration. Poor EABRs on one ear possibly result from the total duration of deafness in this ear and/or compensation by the other ear.

Adult↗
PubMed1980

The progress of adrenoleukodystrophy as revealed by auditory brainstem evoked responses and brainstem histology.

Serial studies of auditory brainstem evoked responses (ABR) and slow vertex responses (SVR) were obtained during the progress of adrenoleukodystrophy in a 6-year-old boy. This child was normal until 5 years of age. His illness began with a gait disturbance, dysarthria, and hearing difficulty. Later, spastic paralysis, serious deafness, and blindness appeared. He died of respiratory failure 2 years after the onset. The ABR was normal at onset but changed to an abnormal pattern. Initially, there was lengthening of the wave V-I interpeak interval. This was followed by the disappearance of the later components as his general condition deteriorated. At the terminal stage, only a prolonged wave I was recordable. The postmortem pathology revealed demyelination of auditory nerves and remarkable neuronal loss in the auditory pathways of the brainstem; in addition, there was a variety of extensive degeneration throughout the cerebrum, in particular the complete degeneration of the white matter with secondarily occurring ganglionic cell changes. These date suggest that degeneration of the brainstem from rostral to caudal levels occurred.

Adrenal Gland Diseases↗
PubMed1987

The maturation of the central auditory conduction in preterm infants until three months post term. II. The auditory brainstem responses (ABRs).

Auditory evoked brainstem responses (ABRs) were recorded in 65 preterm infants (serially in 55 of them), divided into 5 groups, according to their gestational age (GA). The recording sessions were performed at 8 conceptional age levels (CA = GA + chronological age), of which the last two were about 40 and 52 weeks CA. The number of recording sessions varied from one to seven. A full set of ABR latency and amplitude parameters was analyzed including peaks I, II, IIN, III, V and IIc, IIINc and Vc as well as some interpeak latency differences (IPLDs), and the amplitude ratios. The detectability of the different components in the ABR tests at 70 dB reached 80-100% at about 32 weeks CA. The side of stimulation nor the state of vigilance influences the detectability. The degree of prematurity in the 5 GA groups did not influence the development of the parameters. Neither the side of stimulation nor generally the state of vigilance give rise to different parameter values. The thresholds show an age dependent decrease, which is also determined by central maturation. The differential development of the latency decrease of the ABR parameters with increasing conceptional age can be associated with morphological maturational processes and may add weight to the arguments in the delineation of the sources of the ABR. The ipsi- and contralateral central conduction V-II and Vc-IIc do not show latency differences at any CA level. The components IIc and Vc, however, lagged behind in absolute latency compared with II and V. It is concluded that the ABR is a powerful instrument for the study of the maturation of the human auditory pathway in the brainstem. In view of the variability, the detectability and the complex changes within the ABR during the preterm period, its application for clinical purposes during this period has a limited value.

Analysis of Variance↗
PubMed1981

[Diagnostic value of brainstem auditory evoked potentials (author's transl)].

The present work is an evaluation of brainstem auditory evoked potentials (BAEP) as a tool for neurological diagnosis. Filtered alternate clicks with monaural stimulation and ipsilateral recording between the vertex and the ipsilateral mastoid have been used. Normative data of the laboratory established in 50 normal subjects, mean age 35 years, and criteria for interpretation are given. 155 patients had or were suspected of having multiple sclerosis. In definite multiple sclerosis (33 patients), BAEP were abnormal in 67 p. 100 of the cases, among them the 4 patients with an internuclear ophtalmoplegia. In probable multiple sclerosis (54 patients) BAEP were abnormal in 41 p. 100 of the cases and in possible multiple sclerosis (68 patients) there were 19 p. 100 with abnormalities. Results show that BAEP are clearly a useful tool for diagnosis in progressive paraplegia, in optic neuritis, and in cases in which symptoms and signs lead to discuss posterior fossa tumours. In 66 patients with suspected or proved tumours (acoustic neurinomas excluded) and in 25 patients with vascular disease, the contribution of BAEP to neurological diagnosis is of unequal interest. In some cases BAEP only confirmed the data of the clinical examination. When tumours were diagnosed with the CT scan, BAEP could help in pointing out the accurate relation of the tumour with the brainstem and the auditory pathways. In 36 patients the contribution of BAEP was important in establishing the rostral extension of bulbocervical tumours or, mainly, in indicating the presence or absence of infiltrating brainstem tumours which were not clearly apparent on the CT scan.

Adult↗
PubMed2001

Auditory brainstem response and temporal bone pathology findings in a brain-dead infant.

The criteria for assessing adult brain death have been already established, but those for infant brain death have not been yet established in Japan. We report auditory brainstem response (ABR) and postmortem pathology of the temporal bone and brain of a brain-dead 9-month-old female. During the comatose state, her ABR showed only waves I and II bilaterally. Autopsy revealed the presence of a left cerebellar astrocytoma, herniation and anoxic encephalopathy. The pathological examination of the temporal bone revealed the destruction of the inner ear particularly on the left side. In the auditory pathway of brain-dead patients, degeneration occurs first in the cerebrum, followed by the cochlear nerve. Thus, ABR is one of the useful means to assess brain death even in infants.

Astrocytoma↗
PubMed1993

Hearing impairment resulting from a pineal region meningioma.

Because of extensive interconnections within the auditory pathways, hearing impairment from a central origin is rare. We describe a patient with a large pineal region meningioma in whom hearing loss was the predominant symptom. The patient promptly recovered hearing after the surgical removal of the tumor. The mechanism of this phenomenon is discussed.

Evoked Potentials, Auditory, Brain Stem↗
PubMed1987

Low-frequency sensorineural hearing loss: a syndrome.

Eleven patients were found to have a pattern of bilateral, predominantly low-frequency sensorineural hearing loss and disproportionate speech discrimination scores. These patients were submitted to pure-tone audiometry, Arabic speech audiometry, immittance, auditory brainstem response, middle-latency response, Arabic central auditory tests, EEG and computerised tomographic (CT) scan. Results pointed to a lesion in the central auditory pathway. Two possible etiological factors were considered: infection and epilepsy of the temporal lobe. This disease pattern should raise the audiologist-otologist's index of suspicion necessary for its identification and planning of further investigations. This will help determine the etiology and true nature of the syndrome.

Adolescent↗
PubMed1996

Studies of multimodal evoked potentials in treated phenylketonuria: the pattern of vulnerability.

We performed studies of multimodal evoked potentials and peripheral sensory and motor nerve conductions in 33 early and 6 late treated patients with phenylketonuria. The studies revealed the following picture: 1. In 27% of early treated patients latencies of visual evoked potentials were increased. The cause for these changes in unknown. 2. Nerve conduction studies showed the presence of a minor sensory neuropathy which in rare cases may also affect peripheral motor nerves. This neuropathy did not have features of a central-peripheral distal axonopathy which argues against a toxic/nutritional causation. 3. Deficits in the central sensory, motor, and auditory pathways were present, but rare in early treated patients. If the results of electrophysiological studies reported by different groups are compared, the emerging picture is very similar and the majority of the-minor-differences is likely to be explained by technical aspects.

Adolescent↗
PubMed2004

Electrophysiologic and objective monitoring of the cochlear implant during surgery: implementation, audit and outcomes.

Electrophysiologic and objective measures are reviewed with respect to their implementation as monitoring tools for cochlear implants in the operating room and their value in the management of children. The current intraoperative test protocol in Nottingham consists of back-telemetry (BT) diagnostic testing of implant function, including impedance telemetry (ImpT), integrity testing (IT), electrical stapedius reflex response (ESR), electrical auditory brainstem response (EABR) and Neural Response Telemetry (NRT). Of 427 cases of implantation in the period 1990-2003, 303 (71%) were completely normal for all components of the protocol. In the remaining cases, some results were either simply anomalous, with no direct impact on management during surgery, and some were more significant, resulting in actions such as the use of the back-up device or repositioning of the electrode array. Normal intraoperative findings provided immediate reassurance to the implant team and parents of young children that the implant was fully functioning and that electrical stimulation was activating the auditory pathways These objective measures also identified potentially challenging cases, such as those with low levels of sensitivity to electrical stimulation and susceptibility to facial nerve stimulation. An audit showed that intraoperative measures provided valuable assistance in the initial fitting of the device.

Action Potentials↗