The technical, neurological, and psychological significance of ‘alpha’, ‘delta’ and ‘theta’ waves confounded in EEG evoked potentials: a study of peak amplitudes

In a complementary report, the analysis of peak latencies provided evidence that EEG averaged evoked potentials (AEPs) and event related potentials (ERPs) confound ‘delta’, ‘theta’, and ‘alpha’ frequency responses thought to be generated by the ‘brain-stem’, ‘limbic’, and ‘thalamic’ cortical activating systems, respectively. The present report deals with amplitude data obtained from the same sample of 93 adults by recording EEG responses to auditory tones and using narrow-band filters to distinguish ‘4 Hz’, ‘7 Hz’, and ‘10 Hz’ component waves that constitute the unfiltered AEP. Bivariate and multivariate statistical analyses of peak amplitudes provide additional evidence of the distinct and unitary nature of these component waves. Correlations with age, sex, and wakefulness variables confirm that the component waves are associated with systems that maintain behavioural arousal. The amplitude results extend the latency findings by revealing the functional organisation of the three arousal systems in terms of excitatory and inhibitory projections. It is suggested that there are implications for future research on the physiology of brain arousal systems, and for the study of normal personality and temperament, as well as for the diagnosis of psychiatric disorders and the monitoring of drug effects and therapies.