Emotional experience, facial expression, and startle reflex modulation in young adults, healthy older adults, and Alzheimer's disease

Abstract

This study was designed to assess the impact of aging and Alzheimer's disease on conscious appraisal of emotional experience, facial expression, and emotion-modulated action tendencies. Participants included healthy young adults (YA), healthy older adults (OA), and individuals in the early stages of Alzheimer's disease (AD). Self-report of emotional experience while viewing emotionally-salient images was recorded, action tendencies in the form of eye-blink startle reflex modulation and its resolution over time (300ms and 3000ms post-stimulus offset) were recorded, and facial expression of emotion was assessed utilizing EMG recordings of corrugator and zygomatic facial muscles. Consistent with previous studies of emotion in YA, showed the predicted linear relationship with normatively-determined image type (positive, neutral, & negative), and arousal experience ratings were in the predicted quadratic pattern. Corrugator EMG activity increased while viewing negative images and zygomatic EMG activity increased while viewing positive images, as predicted. Startle reflex magnitude was observed in the predicted valenced direction (i.e., greatest for negative images) while viewing images and 300ms post-image removal, but this pattern inverted at the 3000ms probe-time. Similar findings were observed in a comparison of the YA and OA groups, however a difference was observed in the resolution of the startle reflex, with the expected valenced pattern dissipating by the 300ms probe-time for the OA group. Comparisons of the OA and AD groups were limited by small sample sizes, but the AD group was similar to the OA group on measures of self-report of emotional experience patterns and corrugator EMG activity. Zygomatic EMG activity while viewing positive images appeared reduced in the AD group, and no effect of startle reflex modulation was observed in the AD group. The implications of these findings are discussed.