Orienting, emotion, and memory: Phasic and tonic variation in heart rate predicts memory for emotional pictures in men
Arousal-related processes associated with heightened heart rate (HR) predict memory enhancement, especially for emotionally arousing stimuli. In addition, phasic HR deceleration reflects “orienting” and sensory receptivity during perception of stimuli. We hypothesized that both tonic elevations in HR as well as phasic HR deceleration during viewing of pictures would be associated with deeper encoding and better subsequent memory for stimuli. Emotional pictures are more memorable and cause greater HR deceleration than neutral pictures. Thus, we predicted that the relations between cardiac activity and memory enhancement would be most pronounced for emotionally-laden compared to neutral pic – tures. We measured HR in 53 males during viewing of unpleasant, neutral, and pleasant pictures, and tested memory for the pictures two days later. Phasic HR deceleration during viewing of individual pic – tures was greater for subsequently remembered than forgotten pictures across all three emotion catego – ries. Elevated mean HR across the entire encoding epoch also predicted better memory performance, but only for emotionally arousing pictures. Elevated mean HR and phasic HR deceleration were associated, such that individuals with greater tonic HR also showed greater HR decelerations during picture viewing, but only for emotionally arousing pictures. Results suggest that tonic elevations in HR are associated both with greater orienting and heightened memory for emotionally arousing stimuli.
It is well established that emotional arousal at the time of encoding facilitates subsequent memory (Cahill & McGaugh, 1998). When measured prior to or during memorization, elevated heart rate (as one index of arousal) has been associated with better subsequent memory performance (Jennings
& Hall, 1980), particularly in subjects with a history of PTSD (Nagamine, Matsuoka, Mori, Fujimori, Imoto et al., 2007). Pharmacological agents that alter arousal and heart rate (e. g., beta-blockers or epinephrine) show commensurate memory alterations, such that heightened heart rate (HR) is associated with memory enhancement and reduced HR with memory impairment, especially for emotionally arousing information (Cahill & Alkire, 2003; O’Carroll, Drysdale, Cahill, Sha – jahan, & Ebmeier, 1999). In these studies, HR may act as a proxy measure for peripheral (and possibly central) adrenergic and/or noradrenergic activation. Human and animal research suggests that central noradrenergic activation, especially within the baso – lateral nucleus of the amygdala, is necessary for enhancement of memory for emotionally arousing material (Cahill & McGaugh, 1998; van Stegeren, Everaerd, Cahill, McGaugh, & Gooren, 1998). quent memory performance (e. g., Buchanan et al., 2006; Palomba, Angrilli, & Mini, 1997; Siddle, Packer, Donchin, & Fabiani, 1991). It is currently unclear how heightened HR over an extended
Period of time (on the order of minutes to hours) is associated with phasic decreases in HR during orienting (which occur for only a few seconds). Theoretically, both tonic HR elevation and phasic HR deceleration during picture viewing should predict memory enhancement. The current study included a 25- to 28-min encod – ing period, in which subjects viewed pleasant, unpleasant, and neutral pictures.