Time Dependence of Enhancement Effects in Emotional Memory

Abstract

Extensive evidence from human and animal studies indicates that emotionally arousing events are more likely to be remembered than neutral events. This phenomenon is known as the emotional enhancement of memory (EEM) and is attributed to emotional modulation either of different memory stages,including encoding and consolidation,or memory phases,including shortand long-term memory. Current theories on emotional memory suggest that EEM effects occur via modulation of the amygdala and other related cerebral regions,including the hippocampus and prefrontal cortex. In light of the time dependence of consolidation observed in animal studies,it is necessary to conduct an integrative investigation of both the time-dependent effects of emotional memory and the effects of emotional arousal and valence on human memory. A multifactorial experimental design of 2×4 (times×picture categories) was used. Experiments comprised encoding and recognition sessions. Each subject (n=20) completed one encoding phase and two recognition phases,one after 20 min to measure short-term recognition (R1) and one after 24 h for long-term recognition (R2). During encoding,subjects were required to rate the picture on a three-point emotional intensity scale (1=low,2=medium,3=high) and to remember the picture. During R1 and R2,320 pictures were presented,half of which had been presented during encoding and the other half had never seen by the subject. Subjects were instructed to indicate whether each picture was "old" or "new" by pressing a key. Behavioral data were analyzed using SPSS 10.0 software. The arousal level was highest for fear,moderate for happiness and sadness,and lowest for neutral feelings. EEM effects were correlated with the highest arousal for short-term memory (Pr:F(3,76)=7.50,P0.001; d':F(3,76)=7.76,P0.001) and with arousal levels,but not valence,for long-term memory (Pr:F(3,76)=32.76,P0.001,d':F(3,76)=29.86,P0.001). Moreover,dissociation of EEM effects was observed between different arousal levels and time courses. Interactions between times (R1 and R2) and groups (fear,happiness,sadness and neutral) were significant (Pr:F(3,152)=6.89,p0.001). The results confirm that emotional modulation of different stages of memory is time-dependent and that time-dependent EEM effects are predominantly associated with arousal levels,but not emotional valence. Moreover,dissociation of EEM effects between different arousal levels and time courses was observed.