Human slow auditory evoked potentials during natural and drug-induced sleep.

The alterations of human slow auditory evoked potential (SAEP) were studied during the sleep-waking cycle. Simultaneous recording of the mean square and standard error curves proved helpful in obtaining more information on the EEG samples used for averaging. In both natural and drug-induced sleep the earlier SAEP components decreased or disappeared, while the later components increased. A significant lengthening of all SAEP peak latencies was found in all sleep stages during tone-burst stimulation. With click stimulation the peak latencies of most SAEP components remained constant. Due to the variability of individual SAEPs, the interpretation of averaged SAEPs was commonly more difficult in sleep as compared with wakefulness. The alterations of SAEPs during sleep are considered from the point of view of their exrralemniscal origin. The hypothesis is put forward that the activating (desynchronizing) and depressing (synchronizing) systems participate in the generation of the earlier and later SAEP components, respectively.

Intramodal and interaural interactions of the human slow auditory evoked potential.

It is proved that the human slow auditory evoked potential (SAEP) possess intramodal (frequency) and interaural specific properties. It is shown that tonotopic and bilateral organization of the SAEP generating system is better expressed at lower stimulus intensities. It is concluded that neuron populations of the SAEP generating system which perceive less different tone stimuli overlap each other greater than those which perceive more different stimuli. The data on intramodal and interaural specificity of SAEP are discussed from the point of view of its extralemniscal origin.

The reliability of averaging technique in registration of slow auditory evoked potentials in man.

The authors studied the application of arithmetic averaging in the registration of auditory evoked potentials (AEP). Fourier analyses of averaged potentials show a typical shape of both amplitude and phase spectra in the region of the AEP. The maximum of the amplitude spectra diminishes with lower sound intensities and shifts to lower frequencies. The enhancement of the mean power of the EEG in the region of the AEP demonstrates the suitability of the arithmetic averaging technique in the Electric Response Audiometry. For clinical practice the simultaneous registration of the arithmetic mean and the mean square value along with the standard deviation is useful to detect artifacts or amplitude and latency shifts of the AEP components.

[Problems of the electric response audiometry (ERA) during the natural and artificial sleep (author's transl)]. / Probleme der "Electric Response Audiometry" (ERA) während des natürlichen und künstlichen Schlafs

The investigators carried out threshold determinations on 16 children and 6 adults in wakefulness, under general anaesthesia (we used chloral hydrate anaesthesia) and in sleep (stage II-III and stage REM). Falling asleep (stage I and initial stage of anaesthesia respectively) the latencies of the individual components of the acoustically evoked potentials are prolonged in mean of 30 msec. Simultaneously the amplitude of N1 significantly decreases and N2 becomes a prominent point (Fig. 1). The generation mechanisms of wave N2 are obviously different from those of wave N1. Its input-output curve takes a very steep course (Fig. 5) and the shortening of latencies increases with growing intensity of stimulus too (Fig. 4). Amplitude histogrammes demonstrated the dependency of the form of the acoustically evoked potential on the degree of synchronisation of EEG activity. While in the case of desynchronisation N1 appears more markedly, N2 does in the case of synchronisation. The mean deviation of the ERA threshold totals plus 3.8 +/- 6.9 dB (n = 41) under chloral hydrate anaesthesia, plus 4.9 +/- 6.7 dB (n = 37) in natural sleep in contrast to the wakefulness. With a 99% confidence there occur confidence intervals ranging from + 1 to + 7 dB and from +2 to +8 dB respectively. In identifying the threshold potentials error I (existing potential not recognized) occurred in 15-20%, error II (random wave seen as potential) in 20% of these studies. All these experiments showed significant lower variances for the latencies compared with variancies of amplitudes. The variance of amplitudes is smallest in children (Table 1) under general anaesthesia as well as in adults in wakefulness (Table 2). For the practical performance of ERA chloral hydrate is recommended for studies on children. A uniform EEG-state as well as a uniform depth of sleep are basic conditions for ERA during sleep, sedation or under anaesthesia. These conditions must constantly be controlled by EEG, EOG and EMG.

ERA-stimulation with free-programable frequency and intensity sequence--a method to reduce the examination time.

A new method for ERA-stimulation with free-programable sequence of intensity and frequency will described. We developed to realize this method a Free-Programable ERA-Stimulator, FPERAS/74. The expectation has been confirmed that this way of stimulation which includes a regular change of frequency and intensity of the auditory stimuli decreases effective the development of habituation in its amount and velocity. In our experiment (K- and P-experiment) it will be clarified the efficiency of this method both with regard to the time-saving during the recordings of the AEP and its quality comparee with the conventionally determined AEP. It can be stated a triple shortening of the examination time with a simultaneous improvement of the quality and the reproductibility of the AEP.