1

Spontaneous electrical activity from the scalp was first recorded by Berger in 1929, and this activity is now routinely recorded in the electroencephalogram (EEG). In trying to find electrical activity from the inner ear, Wever & Bray (1930) successfully recorded potentials from the round window of a cat in response to sound stimulation. These potentials approximated the acoustic waveform of the sound, and Adrian (1931) suggested that the responses were generated in the cochlea by some form of microphonic action. They have since become known as the cochlear microphonic (CM). In 1935, Fromm et al made recordings from the round window and the promontory in the human ear, and a similar technique during surgery was later referred to by Lempert et al (1947) as electrocochleography.

Studies were also made on alterations in electroencephalographic recordings in response to sound stimuli. Davis et al (1939) noticed consistent changes in the EEG in response to repeated auditory stimulation. These auditory evoked potentials were best recorded from the vertex, and were initially called ‘V’ potentials. However, the responses were very small and difficult to measure against the ongoing electrical activity of the brain. Particular difficulty was experienced when the stimuli were of low intensity, as the voltage of the EEG was much greater than that of the evoked potentials. It was therefore not possible to utilize this method for estimation of hearing thresholds with the technology available at that time.

The development of averaging computers facilitated more accurate analysis of small bio-electrical signals. Dawson (1951) was the first to describe a summation technique for the detection of small evoked potentials from the ongoing EEG, and it has since become possible to utilize evoked potentials generated within the auditory system as clinical audiometric tests. The technique of recording the action potential of the cochlear nerve from the round window in an anaesthetized patient was described by Ruben et al (1962). Later a transtympanic technique was popularized by Portmann & Aran (1971). In this technique, a 0.1 mm, insulated, needle electrode is passed down the ear canal through the tympanum to rest on the bony promontory. This technique is now known as transtympanic electrocochleography. Recordings have been made also from electrodes placed in the external ear canal (Yoshie et al 1967, 1971), and from non-invasive surface electrodes placed on the ear lobe and the vertex. The latter technique was described by Sohmer & Feinmesser (1967), who later showed that in addition to the cochlear potentials there were some later waves representing the neural discharge from the brainstem (Sohmer & Feinmesser 1973). Working on animals and later recording from the scalps of humans, Jewett et al (1970, 1971), independently, described the origins of the so-called ‘far-field’ auditory brainstem potentials recorded from the scalp in response to click stimuli. Middle latency neurogenic responses were described by Mendel & Goldstein (1969). However, in this latency response the potentials were first recorded by Geisler (1958). Other potentials generated along the auditory pathway were also identified. Thousands of research papers and studies on the clinical application of auditory-evoked potentials have been published since that time. Further research in developing stimulation and recording methods is required to optimize EP (evoked potential) techniques for clinical practice.

Stay updated, free articles. Join our Telegram channel

Join