ABSTRACT

Arousal may be defined as a continuum of states of mental activity, ranging from deep sleep to drowsiness, alert wakefulness and agitation. “Activation” is sometimes used as a synonym or related construct. The psychological theory of arousal originated in studies using the electroencephalograph (EEG) to assess central nervous system (CNS) function, pioneered by H. Berger in the 1920s. Researchers of the 1940s and 1950s, such as D. Lindsley, noticed a correspondence between the pattern of electrical activity recorded from scalp electrodes and the person’s state of wakefulness (for a review of early studies, see Duffy 1962). Alert, mentally active subjects showed predominantly low amplitude waveforms, with a frequency of 13-30 Hz (b waves). As arousal decreased, amplitude tended to increase and frequency decreased, generating a waves (relaxed state 8-12 Hz) or q waves (drowsy state 4-7.5 Hz). At the same time, animal studies showed that stimulation of the reticular formation provoked both behavioral activation and concomitant changes in the EEG. Studies suggested that arousal may also be indexed by measures of autonomic nervous system (ANS) activity. Measures such as heart rate, electrical conductance of the skin and constriction of vascular muscles are linked to arousal associated with the “fight-or-flight” reaction, and the sympathetic branch of the ANS.