Sleep and Other Behavioral States Reflected in Cardiovascular Response Patterns

Abstract

the behavioral state of an organism can be operationally defined as a set of physiological and behavioral variables that may be measured at any point in time (1). Behavioral states such as arousal or sleep produce centrally mediated changes influencing many physiological and behavioral systems. These widespread and sometimes long-lasting changes also differentiate behavioral states from more discrete behavioral acts such as the flexion or extension of a limb. Behavioral states may be defined in terms of observable somatic behaviors as they differ relative to other behaviors. Alternatively, physiological measures such as the electroencephalogram (EEG) or cardiorespiratory parameters may differentiate one state from another. For example, the behavioral manifestations of sleep in an organism lead one to impute a “sleep state” to the central neural activity in progress at a certain time in that organism, but measurement of eye movements or of the EEG allows one to divide the sleep state into rapid-eye-movement (REM) and non-REM (NREM) states, each of which has been shown to have different physiological implications for the organism. Application of the behavioral state concept to the awake situation is more difficult because there is a wide variety of normal waking behavior, from the simple actions of eating, walking, or lifting to the complex acts of communication or play and complex states characterized by displays of anger or fear. In each of the examples there is an observable set of behavioral events and environmental circumstances that lead one to postulate the existence of a certain “state” of the nervous system that has as its basis various levels of activity of particular regions of the brain or possibly chemically defined systems of the brain. In a recent survey of investigations concerning central nervous system control of behavioral states, Hobson et al. (3) noted the conceptual shift from the belief that states are mediated by neural activity in unitary “centers” to the view that behavioral state control involves the interaction of multiple, anatomically distributed sets of neurons.