Haim Sohmer

Sources of averaged neural responses recorded in animal and human subjects during cochlear audiometry (Electro-Cochleogram)

SummaryThe five waves comprising the averaged neural response (cochlear audiometry or electrocochleogram) to click acoustic stimuli were recorded with pinna and scalp electrodes in both human and animal subjects. The latencies and waveform of the waves in the cat were similar to those recorded in human subjects. Recordings in the cat with pinna-scalp electrodes simultaneously with intracranial recordings from auditory nuclei in the same animal, lead to the following conclusions concerning the sources of these waves in cats and probably in man also: 1. the first response wave is generated by the first order cochlear nerve fibers; 2. the second wave is generated mainly in the cochlear nucleus; 3. the third wave is generated in the superior olivary complex; 4. the fourth and fifth waves are generated in the inferior colliculus. Thus, this recording system provides a convenient means of measuring the neural activity of the cochlea, the brain stem auditory nuclei and the cerebral cortex in human subjects.ZusammenfassungAbleitungen der gemittelten neuralen Potentiale der menschlichen Cochlea auf “Klick-Reizung” mit Elektroden am Ohrläppchen und Vertex (Electro-Cochleogram oder Cochleare Audiometrie) ergeben einen Wellenkomplex aus 5 Komponenten.Mit der gleichen Elektrodenanordnung konnte auch bei der Katze eine ebenfalls 5wellige Antwort auf Klick-Reizung erhalten werden.Dieselbe Elektrodenanordnung ermöglicht auch die Erfassung der Hirnrinden-Antwort auf akustische Reize (Evoked Response Audiometry).Registriert man die extracraniale Antwort simultan mit der elektrischen Antwort aus intracraniell eingepflanzten Elektroden der Cochlea, von der Fenestra rotunda, so erscheint die erste Welle des Antwortkomplexes gleichzeitig mit dem Aktionspotential der Cochlea (N1), die zweite gleichzeitig mit derjenigen bei direkter Ableitung vom Nucleus cochlearis. Der dritten Welle im Komplex entspricht eine Antwort, die vom Nucleus olivarius superior abzuleiten ist. Gleichzeitig mit der vierten and fünften Welle des Antwortkomplexes erscheint eine Antwort, die wir vom Colliculus inferior ableiten konnten.

Development of hearing in neonatal rats: Air and bone conducted ABR thresholds

While the human full-term neonate can hear at birth, in the rat the onset of auditory function as monitored by recording auditory nerve-brainstem evoked responses (ABR) has been reported to begin on post-natal day (PND) 12-14 and reaches adult thresholds at about 22 days. In order to determine the factors involved in this late onset and then rapid threshold improvement in rats, the ABR to both air conducted (AC) and bone-conducted (BC) auditory stimulation was determined in neonatal rats. ABR to maximal intensity BC stimuli (55 dB above adult rat ABR threshold--55 dB HL*) could be recorded from PND 7-8 while AC responses to 80 dB HL* stimuli, only from PND 11. The air-bone gap (a measure of conductive immaturities only) disappeared on PND 15. This shows that there are both conductive (external and middle ear--Air-bone gap) and sensori-neural (inner ear--BC threshold) immaturities in the neonatal rat; the conductive factors are resolved by PND 15 while the sensori-neural continue after that. With respect to conductive factors, it seems that the state of the ear canal is not important while the chief conductive factors involved probably include mesenchyme resorption and/or ossicular ossification. The chief sensori-neural factor may be the development of the endocochlear potential. It is likely that the human fetus in-utero undergoes similar stages of development.

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

SummaryThe 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.

Sources of electrocochleographic responses as studied in patients with brain damage

Abstract With electrodes on the ear lobe and vertex, the earliest (within 10 msec after the stimulus) average response to click stimuli consists of five successive waves in both cat and man (electrocochleography). It has been conclusively demonstrated that the first wave in both man and cat represents the compound cochlear action potential. Experimental studies on cats in this laboratory have demonstrated that waves 2–5 are generated in the various brain-stem auditory nuclei. The purpose of the present study was to confirm these sites of generation for man by comparing electrocochleographic responses with clinical evidence in patients with various types of brain lesion, e.g. , brain-stem tumours in adults and brain-stem damages in severely retarded infants. The electrocochleograms were compared with attempts to localize the sites of brain lesions by means of neurological examination, skull X-ray, pneumoencephalogram, EEG, surgery or autopsy. In cases in which abnormal electrocochleographic patterns were recorded, clinical evidence either hinted at or confirmed the presence of a brain-stem lesion. Thus, the first electrocochleographic wave represents the response of the auditory nerve and the later four waves are generated in the brain-stem auditory nuclei.

Cochlear and brain stem responses in hearing loss following neonatal hyperbilirubinemia.

The site of lesion in hearing loss following neonatal hyperbilirubinemia is unclear. Histopathological studies have implicated the brain stem auditory nuclei while other investigations have hinted at a lesion in the cochlea. In order to clarify this issue, attempts were made to record responses from the auditory pathway in 13 patients with hearing loss following neonatal hyperbilirubinemia. The neural response from the auditory nerve was absent in 11 of the 13 patients and present only in response to high intensity stimuli in 2 patients. However, the response of the cochlear hair cells (cochlear microphonic potential) was present in 9 of the 13 patients. In most other cases of sensorineural hearing loss, with no history of hyperbilirubinemia, the hair cell response was absent. This is functional evidence for auditory nerve damage in cases of hearing loss following neonatal hyperbilirubinemia while the hair cells are spared.

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.

Auditory nerve and brain-stem evoked responses in normal, autistic, minimal brain dysfunction and psychomotor retarded children

Abstract In several forms of abnormal behavior in infants and children, the cause is either uncertain or an unspecified organic brain lesion is assumed to be present. Evoked averaged auditory nerve and brain-stem responses to click stimuli were recorded from groups of normal, autistic, minimal brain dysfunction (MBD) and psychomotor retarded children in order to search for electrophysiological evidence for a brain lesion. Most of the control children were awake and most of the experimental children were in sedated sleep but records were also made from some children while awake and again in the same children when asleep and no change was seen in the response traces. In several of the autistic children there were no electrophysiological responses (indicating a profound hearing loss). In several of the psychomotor retarded children the responses from the region of the inferior colliculus were absent. In the other children in the experimental group, auditory nerve and brain-stem responses were recorded with normal response thresholds but abnormal in other ways: the latency of the auditory nerve response was longer than in the normal children. Also, brain-stem transmission time, measured as the time interval from the negative peak of the auditory nerve response to the positive trough of the response from the inferior colliculus, was shortest in the control group and longest in the MBD group. These results thus present electrophysiological evidence for the existence of an organic brain lesion in these children, at least in the brain-stem regions concerned with auditory function. Together with evidence from other studies, there is support for the conclusion that most of the abnormal behavior seen in these patients is due to a diffuse brain lesion.

The depression of the auditory nerve-brain-stem evoked response in hypoxaemia — mechanism and site of effect ☆

During severe hypoxaemia in the cat the ABR was depressed in 2 different patterns: if mean arterial blood pressure (MAP) was maintained then all other evoked potentials (EPs--somatosensory and visual) remained. If MAP was not maintained, all of these EPs were depressed. This study sought to document these different patterns of ABR depression and to ascertain their mechanisms. When MAP fell, the ABR loss began with the later waves and progressed to the earlier waves. These are signs of a central brain lesion. The hypoxaemia, detrimental to normal function of the cardiovascular system, leads to depression of MAP, to a fall in cerebral perfusion pressure and blood flow, to cerebral ischaemia and ABR loss. On the other hand, when MAP was maintained, severe hypoxaemia was accompanied by a depression of all of the ABR waves at the same time. The cochlear microphonic potential was also simultaneously depressed. These are signs of a peripheral, cochlear effect similar to the demonstrated depression of the positive endocochlear resting potential of the scala media and of the cochlear microphonic potential during hypoxaemia. This leads to interference with the cochlear transduction mechanism so that all of the auditory evoked potentials, including the ABR, are simultaneously depressed. These results lead to the suggestion that the ABR abnormalities seen in patients who suffered a hypoxic (anoxic) insult or an ischaemic episode (prolonged interpeak latencies, loss of later waves and finally all waves absent or only the first wave remaining) is always due to ischaemia even when the initial insult was hypoxic.

Routine Use Of Electrocochleography (Cochlear Audiometry On Human Subjects

Owing to dissatisfaction with behavioral hearing tests in infants, newer techniques have been developed based on the recording of cochlear action potentials in man. In this laboratory, good results are obtained using and earlobe clip electrode, due to reluctance to use electrode placement procedures in infants as employed by other authors (perforation of tympanic membrane or needle in skin of external meatus). The contribution of various reference electrode locations to the recorded response is also demonstrated. The usefulness of this technique in diagnosis of hearing impairment in 57 infants and children with suspected hearing loss or uncertain diagnosis is shown.

Psychological Profile of Help-seeking and Non-help-seeking Tinnitus Patients

The psychological profile of tinnitus patients who sought treatment (Help-Seeking, HS) was compared with that of patients who did not seek help (non-help-seeking, NHS) and with normal control subjects. Psychological evaluations as well as hearing, tinnitus loudness, and tinnitus pitch were measured. Overall, the psychiatric symptomatology of HS (n = 50) was more severe with poorer effective coping abilities and externalization of locus of control than NHS (n - 50). However, the psychiatric symptomatology of the NHS was remarkably more severe than that in the normals (n = 73) and more like that in the HS even though they did not turn to treatment. Tinnitus loudness was significantly lower in HS than in NHS subjects. The lower the tinnitus loudness, the higher the psychiatric symptomatology. The trend towards subclinical abnormalities in NHS indicates their vulnerability to pathology and this requires the attention of the therapist in order to increase the patients self-awareness and to suggest preventive coping strategies or relaxation techniques.