Alternative hypotheses concerning the sources of the human brain stem auditory evoked potentials.
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Evoked Potentials, Auditory↗
Biomedical subjects
D K Prasher
Publications and source records attributed to D K Prasher.
Effect of interaural intensity differences on binaural summation of brainstem auditory-evoked potentials.
With binaural stimulation the two specific parameters that can modify the neural responses substantially are the intensity differences and the time of arrival of the stimulus at the two ears; these events on electrophysiological evidence, being mediated at the superior olivary complex and at the inferior colliculus, the origins of Waves III and V respectively. Comparison of the brainstem auditory-evoked potentials to monaural stimulation with that due to binaural stimulation reveals a significant increase only in the amplitude of Wave V. The amount of increase is reduced from 68.7% with equal intensities at the two ears to 44% with a 10-dB interaural intensity difference. With a 20-dB interaural intensity difference the amplitude of Wave V reverts to that due to monaural stimulation. The 68.7% greater amplitude for Wave V was not due to effective increase in loudness sensation on binaural stimulation (which is equivalent to a monaural increase in intensity of 3 dB) but to binaural summation. In contrast to Wave V, Wave III decreased in amplitude below that resulting from monaural stimulation with intensity differences of 10 and 20 dB at the two ears. This supports the suggestion of inhibitory processes at that level of the brainstem. As only Wave V shows binaural summation the region of inferior colliculus is suggested as the site for the occurrence of this phenomenon. Binaural interaction can also be demonstrated within a limited range with intensity differences at the two ears.
Brain Stem↗
Brain stem auditory evoked potentials: significant latency differences between ipsilateral and contralateral stimulation.
A number of electrical potentials can be recorded from the human scalp following acoustic stimulation. The potentials which occur within 10 msec of the stimulus onset have been termed the brain stem auditory evoked potentials (BAEPs). Latency appears to be the most stable measure and in consequence knowledge of the exact limits of normal latency of each wave is important. In this study the effects of ipsilateral and contralateral stimulation on BAEP latencies have been investigated in 23 normal subjects. The exact limits of normal latency of each wave have been established. It has been shown that significant latency differences exist between ipsilateral and contralateral stimulation. Possible hypotheses are put forward to explain the findings which demonstrate that different neural pathways are followed by ipsilateral and contralateral stimuli and that their respective responses can be investigated separately in man using BAEP recordings.
Brain Stem↗
Brain stem auditory evoked potentials: a comparative study of monaural versus binaural stimulation in the detection of multiple sclerosis.
As the latency of these responses is the most stable measure in normal subjects, the present study examines the latency of the BAEP wave forms in multiple sclerosis (MS) with a view to comparing a monaural stimulation with binaural. In previous studies binaural stimulation has been used to detect MS in clinically 'definite' cases. In this study both clinically definite and possible MS cases were examined and it was shown that in the clinically definite MS category the detection rate improved from 70% to 90% with ipsilateral/contralateral stimulation. In the possible multiple sclerosis group the detection rate was negligible with binaural stimulation compared to 67% with monaural stimulation. Both inter-wave latency and the repeatability of the response in the different groups are discussed in detail.
Acoustic Stimulation↗
The influence of stimulus spectral content on rise time effects in cortical-evoked responses.
A tone burst with a fast rise time elicits a large-amplitude cortical response which reduces markedly as rise time is increased. This effect is not observed with white-noise bursts. It is suggested that where changes in rise time affect the spectral content of the stimulus, a change in response amplitude is encountered. The increase in the latency of the response with increase in rise time is found to be the same for both tone and noise bursts, hence independent of spectral composition.
Acoustic Stimulation↗
A microprocessor controlled multi-channel evoked potential data acquisition system.
A stored program control system is described for the acquisition of evoked potential (EP) data. It is a small, portable and flexible system with a variety of input and output possibilities. The system presents a low cost solution to the problem of acquisition of evoked potential data. A novel method of converting and reducing sixteen channels of EEG analogue data to their digital equivalent is shown. It is adaptable for the inter active control of experiments and is sophisticated enough to deal with the complexities of experimental control as well as data manipulation. One of the major advantages of the system is that both the sequencing of the functions and their detailed make-up can be readily altered by programming to meet the individual requirements of any given situation.
Analog-Digital Conversion↗
Presence of tinnitus indicated by variable spontaneous otoacoustic emissions.
Spontaneous otoacoustic emissions (SOAE) have been widely studied in normal subjects, and there is evidence of their high frequency stability in repeated recordings. A study to determine the frequency stability of SOAE in 53 of 100 consecutive patients, who presented with tinnitus and in whom SOAE were recordable, was undertaken. Patients were divided into five aetiologically homogeneous subgroups: (i) those with normal hearing and no identified pathology, (ii) those with sensorineural hearing loss of unknown origin, (iii) those with normal hearing, but complaining of tinnitus related to head injury, (iv) those with endolymphatic hydrops, and (v) those with noise exposure. The control group consisted of 20 subjects, selected on the basis of recordable SOAE from 38 volunteers with normal hearing and no tinnitus. The prevalence of SOAE and their inter-session frequency stability (reproducibility and relative frequency shift) were analysed. In contrast to the controls, the tinnitus group had significantly increased frequency variability of SOAE (lower reproducibility and increased relative frequency shift). The prevalence of subjects with SOAE was not notably different between the controls and subjects with tinnitus, if the tinnitus group was considered in toto, but a striking 100% prevalence of bilaterally present SOAE was observed in the tinnitus subgroup with head injury.
Adolescent↗
Diagnostic significance of transtympanic electrocochleography in Menière's disease.
Transtympanic electrocochleography (ECoG) was performed on 32 normal ears, 40 ears affected by hair cell damage without any evidence of endolymphatic hydrops (sensory damage) and 44 ears affected by established Menière's disease. The amplitude of the summating potential (SP) and the amplitude of the action potential (AP) were measured at a click stimulus intensity level of 100 dB HL. The SP amplitude was expressed as a percentage of the AP amplitude. In normal ears, the mean SP/AP ratio was 25% (range 10%-63%). In sensory damage, the SP/AP ratio was 13% (range 0%-29%), and in Menière's ears, the SP/AP ratio was 51% (range 29%-89%). In this series, an SP/AP ratio of 29% provided a diagnostic dividing mark between the sensory damage and Menière's-affected ears. Although this precise division was probably fortuitous, it does suggest that ECoG is a useful tool in the differential diagnosis of these two types of cochlear disorders.
Action Potentials↗
Auditory function in hereditary motor and sensory neuropathy (Charcot-Marie-Tooth disease).
Fourteen patients with hereditary motor and sensory neuropathy (HMSN), 12 of Type I and 2 of Type II, were assessed for auditory dysfunction. Five patients complained of hearing loss and all had pure-tone audiograms outside the normal range, while one patient who did not complain of hearing impairment also had an abnormal pure-tone audiogram. Assessment of loudness function, speech audiometry and brainstem auditory evoked potentials (BAEP) suggested that the hearing loss was the result of VIII nerve dysfunction, a conclusion supported by the abnormality of the electrocochleogram (ECochG) in one patient.
Adolescent↗