The Psychophysiology of Emotions

Abstract The link between affective states and psychophysiological activity has been central to the study of behavior for well over a century. With his publication of The expression of the emotions in man and animals , Charles Darwin (1872) provided a foundation for over 140 years of research into the nature of emotions and their physiological and behavioral manifestations. Darwin suggested the existence of distinct kinds of emotional expressions, both somatic and visceral, that were relatively well conserved across phylogeny, and gradually evolved as a result of their adaptive function. A decade later, William James (1884) first articulated his highly influential theory of emotion where he suggested the subjective experience of certain emotions was the result of particular changes in somatovisceral and behavioral responses. Walter Cannon (1927) provided an early challenge to the Jamesian explanation of emotions as a manifestation of specific patterns of somatovisceral activity. Cannon argued physiological responses were the consequence, not the cause, of emotional processes, and that physiological responses were too undifferentiated to account for the variety of distinct emotional feeling states. Cannon’s views were subsequently strengthened when early research failed to demonstrate replicable and generalizable emotion-specific patterns of physiological activity (Harlow & Stagner, 1932). Subsequent work conducted by Schachter and Singer (1962) also appeared to provide strong evidence that the same pattern of physiological activity (arising from epinephrine administration) could result in the experience of different emotions depending on situational cues, which at the time, lent further evidence to the view that emotions were not caused by specific patterns of activity in peripheral physiological systems (although this perspective has now been thoroughly criticized on a number of grounds, see Friedman, 2010). The consensus view of the relationship between emotion and psychophysiological activity was again challenged with the publication of a seminal paper by Ekman, Levenson, and Friesen (1983) where they attributed much of the previous inconsistency between emotions and physiological functioning to a variety of methodological limitations, such as failure to equate the intensity of different emotions and lack of appropriate synchronization between physiological recordings with the likely onset and offset of the elicited emotion. In their study, Ekman et al. measured heart rate, finger temperature, skin resistance, and forearm flexor muscle tension as participants completed two sets of tasks designed to elicit anger, fear, sadness, happiness, surprise, and disgust. In one task, participants were asked to remember and relive past emotional episodes. Participants also completed a directed facial action task in which they were asked to contract sets of muscles to produce facial expressions associated with each emotion. The authors found that in addition to differentiating positive from negative emotions, combinations of physiological measures could differentiate some negative emotions (eg, fear) from others (eg, anger). Subsequent work suggested that the degree of emotion-specific physiological activity was context-dependent such that the specificity was greatest in real-world emotion induction procedures (Stemmler, 1989), and that different emotion induction procedures appear to elicit different patterns of physiological activity (Zajonc & McIntosh, 1992). Such findings led to a series of meta-analyses conducted by Cacioppo, Gardner, and Berntson (1997) and Cacioppo, Berntson, Larsen, Poehlmann, and Ito (2000) on all published studies comparing the effects of at least two discrete emotions on at least two measures of autonomic nervous system (ANS) functioning. Although the results were mixed, these analyses found some evidence of emotion-specific ANS responses. Similarly, a recent systematic review (Stephens, 2010) on the topic of emotion-specific patterns of autonomic functioning found some evidence that different emotions were associated with various patterns of ANS response. While the review found that there were some differences in ANS correlates across emotions, it also found that no basic emotion was entirely unique across the ANS measurements. Subsequent studies have employed multivariate approaches and reported some success in finding emotion-specific patterns of ANS function. For example, Stephens, Christie, and Friedman (2010) had participants view emotion-inducing music and affective films, while recording various ANS measures. Pattern classification analysis found that ANS variables were able to correctly classify predicted emotions at a rate of 44.6%. Using a comparable approach, Kragel and Labar (2013) found that autonomic measures predicted distinct affective states at a rate of 58.0%. While such findings are a clear improvement over previous univariate approaches, they are far from demonstrating discrete emotion-specific patterns of ANS responses.