Long-latency auditory evoked potentials were recorded from two groups of patients, with and without dementia, and were compared with those from a population of normal subjects ranging in age from 15 to 76 years. A sequence of tones of two different frequencies (1000 Hz and 2000 Hz) was presented and each patient was asked to count the occurrences of the rare (P = 0.15) tones in the sequence. Evoked potential waveforms were averaged separately for the rare and frequent tone. Of the various evoked potential components elicited by the tones, the P3 component (latency 300-500 ms) was found to be the most sensitive to aging in normal subjects. It was also the only component which could be used to differentiate between the demented patients and the normal subjects or non-demented patients. The non-demented patients did not differ from normal in any waveform measure. The magnitude of the latency change of the P3 component in dementia relative to normal was sufficiently large that it may provide a practical and objective measure of dementia in a clinical setting.

The P3 component of the auditory evoked potential has been shown to reflect "endogenous" processes related to cognition. This component was measured serially in seven patients who had confusional states or dementing illnesses that fluctuated in severity over time. The latency of P3 component reflected the clinical impression of changes in mental function for each of the patients. These results suggest that the P3 component of the auditory evoked potential provides an objective serial measure of cognitive state that may be useful in following patients with dementing illnesses and in evaluating the effectiveness of any specific therapy.

This chapter discusses variations in visual evoked potentials under anesthesia. Even though the brain is the target organ of anesthetics, relatively little is known about brain function under anesthesia, and the means of monitoring it are meager. In contrast, abundant research on the heart and lungs, which are secondarily affected by anesthetics, has provided the basis for aggressive, invasive monitoring of circulation, and ventilation. The electroencephalography (EEG) and power spectrum analysis of the EEG have been used to monitor the effects of anesthetics, anesthetic concentration and the patient's response to surgical stimulation, however, the EEG has not been a rewarding tool in these applications since it represents the overall activity of the brain and lacks specificity. Sensory evoked responses may provide a better index of brain function under anesthesia since the ultimate aim of anesthesia is to prevent central nervous system (CNS) registration of sensory stimulation. Visual evoked responses (VERs) are obtained in an awake condition prior to medication and at varying concentrations of halothane in oxygen during surgery. All patients received thiopental induction, followed by anesthetic maintenance with halothane in oxygen, paralysis, and endotracheal intubation. © 1980, Academic Press Inc.