فعالیت عصبی در ارتباط با حافظه اپیزودیک برای زمینه عاطفی

To address the question of which brain regions subserve retrieval of emotionally-valenced memories, we used event-related fMRI to index neural activity during the incidental retrieval of emotional and non-emotional contextual information. At study, emotionally neutral words were presented in the context of sentences that were either negatively, neutrally or positively valenced. At test, fMRI data were obtained while participants discriminated between studied and unstudied words. Recognition of words presented in emotionally negative relative to emotionally neutral contexts was associated with enhanced activity in right dorsolateral prefrontal cortex, left amygdala and hippocampus, right lingual gyrus and posterior cingulate cortex. Recognition of words from positive relative to neutral contexts was associated with increased activity in bilateral prefrontal and orbitofrontal cortices, and left anterior temporal lobe. These findings suggest that neural activity mediating episodic retrieval of contextual information and its subsequent processing is modulated by emotion in at least two ways. First, there is enhancement of activity in networks supporting episodic retrieval of neutral information. Second, regions known to be activated when emotional information is encountered in the environment are also active when emotional information is retrieved from memory.

A small number of functional neuroimaging studies have investigated the brain regions and circuits activated during explicit retrieval of emotionally toned items. In one of the first such studies it was reported that activity in occipital-parietal regions was enhanced during visualisation from memory of previously viewed negative images relative to neutral images [27]. The finding of enhanced activity in sensory regions during emotional memory retrieval was replicated by Taylor et al. [58], who found greater activity in the lingual gyrus (BA 18) during recognition of previously studied negative images, relative to neutral images, in the absence of the modulation of any other retrieval-related activity. In a more recent study, Dolan et al. [11] reported that recognition memory for emotional relative to neutral pictures was associated with activation in the anterior temporal pole and the amygdala, leading these authors to conclude that emotional memory retrieval recruited brain regions specialised for processing the affective significance of stimuli. The present investigation was concerned with characterising the brain activity associated with retrieval of emotionally toned contexts rather than retrieval of items with inherent emotional tone. To the best of our knowledge, only one earlier neuroimaging study [33] has investigated the neural correlates of retrieval of such contexts. The results of this electrophysiological study suggested that activity in the same network that supports episodic retrieval of neutral information is enhanced during retrieval of emotional information. Specifically, it was suggested that the incidental retrieval of emotional contextual information was associated with enhanced activity in the same neural systems that support the conscious recollection and subsequent 'post-retrieval’ processing of emotionally neutral information. In particular, it was suggested that such additional activity would be found in the medial temporal/posterior cortical regions subserving the initial retrieval of episodic information [37] and [49] and in right prefrontal regions supporting the subsequent monitoring and evaluation of the retrieved information (e.g. [48]). The present study employed event-related fMRI to investigate the incidental retrieval of emotional and neutral contexts using a procedure similar to that employed by Phelps et al. [39] (see also [33]) which, unlike most prior studies of emotional memory, did not confound the emotional valence of the retrieval cues with the valence of the to-be-retrieved information. By contrasting the neural activity elicited by a single kind of test item (emotionally neutral words) as a function of the emotional valence of its study context, any difference in the activity elicited by test items belonging to different classes of context can be attributed unequivocally to their respective encoding contexts.