FMRI Study Of The Specific Neural And Cognitive Mechanisms Of Emotional Working Memory

Background and Objective Emotional working memory (EWM) is memory related to emotional events, a special kind of working memory (WM), which is based on modulation of emotion on working memory. Previously, the studies related to modulation of emotion on WM focused on valence effect. The effects of emotion on WM have two coins that WM is enhanced by positive emotion while negative emotion impairs WM. The experiments of animal and drug suggested that the effect of arousal/ hormone on efficiency of WM is consistent with"Yerkes-dodson law", inverse"U"curve. This model suggests that under a certain load/difficulty of tasks and keeping a proper arousal level, efficiency of WM or behavioral performance is up to optimum state, while its decreases under the condition of the high arousal level. There were few imaging studies related to the effect of arousal on WM. In addition,"Yerkes-dodson law"only talks about the effect of arousal, not that of valence, and there are no inverse-"U"-curve relationships between arousal and behavioral performance under the low difficulty of cognition. The modulation of emotion on cognition may be affected by load of cognition. Therefore, the interactions between emotion load and cognition load wait for further investigation.Taken together, The primary goal of this study was to confirm whether"Yerkes-dodson law"is adapted to EWM, and further explore the specific mechanisms of effect of emotional arousal and valence on WM, using multiple factors [3(arousal)×3(valence)]and N-Back paradigms (0,1,2- load level).Materials and Methods 20 healthy subjects (9 males and 11 females) were recruited, ages from 20 to 25 years old. 44 pictures were used in the experiment, including 4 categories of pictures related to fear, sad, happy, and neutral scene. MRI scanning was performed while the subjects conducted tasks. fMRI and behavioral data were analyzed with SPM5/SPM2 and SPSS10.0 software.Results The behavioral results indicated that the differences among all loads were significant in mean response time(F = 14.752, P < 0.001)and in correct rates (F = 20.157, P < 0.001). Under 0-Back level, there were also significant differences between happiness and neutral (sadness/fear) conducting paired-samples t-test (P<0.05) and the time of happiness was shortest, and no differences among all categories of pictures under 1-Back condition. The differences of response time were significant between happiness and the others in 2-Back task (P<0.05) and also between fear with the others (P<0.001). The response time was shortest in happiness and longest in fear.fMRI results suggested that brain regions related to load effect included bilateral DLPFC (dorsolateral prefrontal cortex), bilateral OFC(orbitofrontal cortex), bilateral LPC(lateral parietal lobe), bilateral PI(posterior insula), left D-ACC (dorsoanterior cingulate) / V-ACC (ventroanterior cingulate) and right MPC (medial parietal lobe). The brain regions related to valence effect included bilateral DLPFC (dorsolateral prefrontal cortex), left DMPFC (dorsomedial prefrontal cortex), right OFC (orbitofrontal cortex). The brain regions related to arousal effect included bilateral DLPFC (dorsolateral prefrontal cortex), left ACC (anterior cingulate) and right AM (amygdala). In the 2-Back condition, the activation intensity of the right anterior frontal lobe exhibited happiness > neutral/sadness > fear in turn. The brain regions related to the efficiency of the fear included L-OFC (orbitofrontal cortex), left PC (parietal cortex) and right MPFC (medial prefrontal cortex). The brain regions related to the happiness included left SFG (superior frontal gyrus), bilateral DLPFC (dorsolateral prefrontal cortex), bilateral SPC (superior parietal cortex), left MPC (medial parietal cortex), right HIP (hippocampus) and right OC (occipital lobe). The brain regions related to the sadness included right MPFC (medial prefrontal cortex) and left OC (occipital lobe). In contrast to the neutral, the brain regions related to the happiness included bilateral AM (amygdala), bilateral DMPFC (dorsomedial prefrontal cortex), bilateral SFG (superior frontal gyrus), bilateral MFG (middle frontal gyrus), left IFG (inferior frontal gyrus), bilateral OFC (orbitofrontal cortex) and bilateral IPC (inferior parietal cortex).Conclusions First, the behavioral results indicate that there exist load effects in emotional working memory. Under 2-Back condition, moderate arousing positive emotion enhances WM, while high arousing negative emotion impairs WM. This character is consistent with"Yerkes-dodson law".Second, there are common neural mechanisms between emotional working memory and non-emotional working memory. Modulations of arousal and valence on working memory are related to amygdale and prefrontal cortex and the neural correlates underlying emotional working memory are activated in the right prefrontal cortex, which is consistent with the theory of"Yerkes-dodson law"curve.