Search PubMed⌕ Search

Biomedical subjects

H Sohmer

Publications and source records attributed to H Sohmer.

At least 109 records · Page 6Linked to original sources
PubMed1980

Analysis of auditory nerve-brainstem responses (ABR) in neonates and very young infants.

Auditory nerve-brainstem responses (ABR) to click stimuli were recorded in 26 normal infants when they were neonates and again in the same infants when they were 3 months old. The cochlear microphonic potential was also recorded in several of the neonates. The following response parameters were studied: latency and amplitude of the auditory nerve response, amplitude of the brainstem response elicited from the region of the interior colliculus, the ratio of the amplitudes of these two waves and brainstem transmission time (BTT): the time interval between these two responses. It was found that the auditory nerve response is only slightly prolonged in neonates with respect to adults and shortens by a small amount from birth to the age of 3 months. The latency of the auditory nerve response in neonates is only about 0.3 ms longer than in adults. BTT is longest in neonates and shortens significantly in 3-month-old infants.

Acoustic Stimulation↗
PubMed1980

The source along the basilar membrane of the cochlear microphonic potential recorded by surface electrodes in man.

In order to determine the region along the basilar membrane which contributes to the recorded CM, an attempt was made to record CM responses in subjects with normal hearing and in subjects with high frequency cochlear hearing losses (e.g. acoustic trauma). In such cases of high frequency hearing loss, one may assume that damage has occurred to the hair cells in the basal turn of the cochlea. The CM, elicited by one cycle sinusoidal stimuli of various frequencies, intensities, phases, etc., was recorded by means of earlobe and scalp vertex electrodes. The CM recorded in subjects with normal hearing to high frequency sounds showed (besides the previously reported properties of the CM) large amplitudes and short latencies in response to low frequency stimuli. On the other hand, the CM recorded in subjects with high frequency hearing loss were either prolonged in latency and small in amplitude or completely absent. A plot of the relationship between CM lastency to high intensity 500 HZ stimuli stimuli and audiometric hearing loss in 66 ears shows clearly that in those cases in which hearing was normal at frequencies up to about 8 kHZ, CM latency was very short. On the other hand, in those cases in which the high frequency hearing loss progressed to include more and more lower frequencies, CM latency was more prolonged and smaller in amplitude until CM could no longer be observed. These results indicate that the CM recorded in normally hearing subjects from skin electrodes in response to low frequency (500 HZ) stimuli is generated in the basal turn of the cochlea. This finding is probably a consequence of the form of the mechanical response of the basilar membrane (travelling wave) to low frequency stimuli.

Acoustic Stimulation↗
PubMed1979

A functional measure of brain activity: brain stem transmission time.

Surface-recorded auditory nerve and brain stem responses are being used routinely for diagnostic purposes in man. When interest is in auditory diagnosis, the electric response threshold is of primary importance. However, when used in neurological diagnosis, the wave form of the response is important. As a measure of one aspect of response wave form, this paper suggests the use of brain stem transmission time (BTT), defined as the time interval between the first earlobe-negative wave (response of the auditory nerve--the 'input' to the brain stem) and the earlobe-positive wave from the region of the inferior colliculus (the 'output' of the brain stem). The paper shows that BTT is longest in neonates, approaches adult values at the age of about 3 years, is relatively independent of click intensity, conductive hearing loss (middle ear lesion), click rate (except for high rates) and click frequency (filtered clicks). The finding that in a given age group, BTT is generally independent of most stimulus conditions, makes it a useful functional test of brain stem activity.

Adolescent↗
PubMed1978

Auditory nerve and brain stem responses. Comparison in awake and unconscious subjects.

The recording of auditory nerve and brain stem responses to click stimuli is being used for the diagnosis of several conditions such as suspected hearing loss and suspected neurological disorders. The responses obtained in the patient group (often infants and children) are compared with those obtained in normal subjects of similar age who, for ethical reasons, are not sedated. In this study, recordings were made in normal subjects while they were awake and when they were unconscious in drug-induced sleep (being prepared for dental surgery). No significant difference could be observed between the recordings obtained in the awake state and when unconscious in the same subjects. Therefore, one is justified in using recordings made in awake subjects as controls for recordings made in other unconscious patients.

Brain Stem↗
PubMed1978

Evidence from auditory nerve and brainstem evoked responses for an organic brain lesion in children with autistic traits.

In an attempt to resolve the question as to whether children with autistic traits have an organic nervous system lesion, auditory nerve and brainstem evoked responses were recorded in a group of 15 children with autistic traits. The most obvious results included a longer response latency of the auditory nerve and a longer brainstem transmission time, compared to normal children. Five of the autistic children were found to be profoundly deaf. These results strengthen the theory that an organic lesion of the nervous system can give rise to autistic traits.

Autistic Disorder↗
PubMed1978

Brain lesion diagnosis by recording cochlear and brainstem responses to sound stimuli.

A technique has been developed for the recording of the cochlear action potential (electrocochleography) and the brainstem evoked responses to click stimuli by means of earlobe and scalp electrodes with an average response computer. This technique has already proved its usefulness in diagnosis of hearing loss. Since the brainstem responses are generated in the successive brainstem auditory nuclei and since the auditory nuclei and pathways constitute a relatively large volume of brainstem tissue, there is reason to believe that this same technique can also contribute to the diagnosis of brain stem lesions and their localization. When these recordings were made in patients with clinical signs of brain stem involvement, one (or more) of the usual response waves was smaller in amplitude, prolonged in latency, or completely absent. Recording of the cochlear and brainstem evoked potentials thus seems to be a new, simple and rapid tool for the diagnosis of brainstem lesions.

Acoustic Stimulation↗
PubMed1977

Usher's syndrome: electrophysiological tests of the visual and auditory systems.

The symptoms of Usher's syndrome - congenital hearing impairment and tapetoretinal dystrophy - are difficult to detect in young children. The electroretinogram (ERG), visual evoked potential (VEP), auditory nerve and brain-stem responses as well as the cochlear microphonic potentials were used to evaluate the defects of the visual and auditory systems in 20 patients, 3-45 years of age. This study demonstrates the usefulness, reliability and convenience of the electrophysiological tests for early diagnosis and functional evaluation of Usher's syndrome.

Adolescent↗
PubMed1977

Correlations between psychophysical magnitude estimates and simultaneously obtained auditory nerve, brain stem and cortical responses to click stimuli in man.

Responses from the auditory nerve, brain stem auditory nuclei and cortex, as well as subjective responses to click stimuli at 10 intensities, were recorded simultaneously in the same human subjects. For various measures of the responses, the power-law exponents of their intensity functions were calculated, along with their statistical significances. The electrophysiological and psycho-physical functions were compared for similarity. On average, the exponents of the intensity functions of amplitudes of the auditory nerve and earlier brain stem responses were highly significant, showing similarity across subjects and similarity with the exponents of the subjective estimates. However, a closer examination proved this similarity to be superficial, since magnitude estimates showed an appreciable intersubject and intersession variability while the auditory nerve and brain stem responses were approximately constant. All other electric response measures either had exponents which were not significant or showed even poorer correlation with the subjective response. It is proposed that the type of electrical activity recorded in this study may not be the proper set of neural parameters which give rise to the loudness estimate.

Acoustic Stimulation↗
PubMed1977

Identification and separation of acoustic frequency following responses (FFRS) in man.

Frequency following responses (FFRs) to monaural tone bursts were recorded in normal and hearing impaired subjects as the potential difference between an ipsilateral earlobe electrode and a scalp vertex electrode. Whenn the rubber tube coupler between the earphone and the subject's ear was clamped, a stimulus artefact FFR was occasionally recorded. The "biological" FFR had a latency of about 1 msec and an irregular wave form which was made more sinusoidal by the addition of white noise. When the responses to tone bursts of opposite onset phases were added together, a "double frequency" FFR was obtained which had a latency of about 6 msec and whose amplitude was appreciably reduced by white noise. In some hearing impaired subjects (with no neural responses to clicks), this longer latency double frequency component could not be recorded, while in those cases in which the cochlear microphonic potential could be recorded, the shorter latency FFR was also present. It is concluded that the FFR in normally hearing subjects is made up of a short latency cochlear microphonic component and a longer latency neural component.

Adolescent↗
PubMed1977

Sources of frequency following responses (FFR) in man.

In order to study the sources and pathways which are responsible for the frequency following response (FFR), records were made in control subjects and in patients with special types of lesion and response. It has already been shown that the FFR in normal subjects to tone bursts with single onset phases is made up of a short latency cochlear microphonic potential (CM) and a longer latency neural component (neural FFR). No neural FFR could be recorded in patients with upper brain-stem lesions (absence of click-evoked responses from the inferior colliculus along with clinical signs of such a lesion). Their FFR was exclusively a cochlear microphonic potential, thus demonstrating that the neural FFR with a latency of 6 msec is generated in the region of the inferior colliculus. Also in subjects with large post-auricular muscle (PAM) responses, the PAM can contribute to the FFR, with a latency of 10 msec. In patients with high-tone hearing loss due to acoustic trauma, no CM could be recorded while a neural FFR with a latency of 6 msec was present. This indicates that the CM recorded by this technique may be generated in the basal turn. It also demonstrates that the pathway of the neural FFR begins in the apical turn of the cochlea.

Adult↗
PubMed1976

Intensity and rate functions of cochlear and brainstem evoked responses to click stimuli in man.

The complex of five waves, which are the responses to click stimuli of the auditory nerve and the brainstem auditory nuclei, were recorded in ten human subjects by means of earlobe and scalp electrodes. The rate of the stimuli was varied from 5/s to 80/s and their intensity was varied over a 70 dB intensity range in order to study the rate and intensity functions of each of the response components. With increasing click intensity, the amplitude of the first wave (generated by the auditory nerve) increased proportionally while the amplitudes of the later waves (generated by the brainstem auditory nuclei) reached their maximum amplitudes at intermediate click levels (saturation), and at high intensities occasionally even decreased in amplitude. The latency of each of the waves decreased by similar amounts as the intensity was increased. With increasing click rates, the amplitude of the first wave decreased the most, while there were smaller effects on the amplitude of the later waves. There was no effect of click rate on the latency of the first wave, but the latency of the later waves increased with click rate, the effect being greater on the later waves. In the rate functions, the latency change of a wave was greater than that of the waves preceding it (accumulative effect). These results are explained by overlapping convergence and divergence in the ascending auditory pathway. These results support the notion that the principal component of each wave is activated by the principal component of the previous wave. These results may explain the relative ease with which several workers record the fourth wave of the complex, and their preference for this response.

Auditory Pathways↗
PubMed1976

Recording of the cochlear microphonic potential with surface electrodes.

The cochlear microphonic potential was recorded in human subjects with surface electrodes (earlobe clip and scalp vertex disc) and an averaging procedure. Special precautions were taken to identify and separate artefactual, neural and microphonic components. These included shielding of the earphone, a rubber tube to introduce a time delay between artefact and biological response and white noise to mask the neural component. The cochlear microphonic potential was larger in amplitude in response to low frequency sounds and had a high threshold. Two clinical cases of cochlear hearing loss are presented, both lacking neural responses. The cochlear microphonic potential was present in one of them (i.e., neural hearing loss) and absent in the other (i.e., sensory hearing loss).

Adult↗