Surface facial electromyography reactions to light-relevant and season-relevant stimuli in seasonal affective disorder /

by Tierney Lindsey, Kathryn.

Title of Thesis: Surface Facial Electromyography Reactions to Light- Relevant and Season-Relevant Stimuli in Seasonal Affective Disorder Author: Kathryn Tierney Lindsey, Doctor of Philosophy, 2005 Thesis directed by: Kelly J. Rohan, Ph.D. Assistant Professor Department of Medical and Clinical Psychology Facial electromyography (EMG) activity was recorded from the zygomaticus major and corrugator supercilii muscle regions to examine emotion-specific reactivity in 24 currently depressed individuals meeting DSM-IV criteria for Major Depression, Recurrent with Seasonal Pattern, and no other current Axis I diagnosis, and 24 controls with normal mood and no history of depression. Based on models of seasonal affective disorder (SAD) and a proposed role for learned associations between depressive behavior and environmental stimuli signaling low light and winter season, participants were exposed to light- and season-relevant environmental stimuli and were asked to imagine what they would be feeling and thinking if they were actually in the picture. Skin conductance response was also assessed to determine participants’ general sympathetic arousal to the stimuli. Results indicated that SAD participants: 1) responded to bright light stimuli with decreased corrugator mean EMG activity relative to low light stimuli; 2) demonstrated no increases in zygomatic mean EMG activity to bright light stimuli; 3) reported an exacerbation of baseline depressed mood following low light and winter stimuli and an iv improvement in depressed mood following bright light stimuli; and 4) evidenced increased SCR magnitude to bright light stimuli as compared to low light stimuli. Notably, corrugator and self-report mood ratings support previous findings of heightened psychophysiological reactivity and exacerbated depressed mood after exposure to lightrelevant stimuli in SAD and suggest that light intensity may be more salient than seasonal cues in determining affective reactivity. Further research is needed to understand how these associations develop, and to establish the clinical implications for psychophysiological measures in SAD assessment and treatment monitoring. v