Brain Imaging Investigation of the Memory-Enhancing Effect of Emotion

We present a protocol that uses functional magnetic resonance imaging to investigate the neural correlates of the memory-enhancing effect of emotion. This protocol allows identification of brain activity specifically linked to memory-related processing, contrary to more general perceptual processing, and can be used with healthy and clinical populations.

The aim of this experimental protocol is to identify brain activity specifically linked to the memory enhancing effect of emotion. This is achieved by implementing the subsequent memory paradigm with emotional stimuli. This paradigm consists of an encoding task and a retrieval task.

During the encoding task, participants are presented with emotional and neutral stimuli, and during the retrieval task, their memory for the items presented during encoding is tested. Typically, brain imaging data are recorded during the encoding task, but it may also be recorded during the retrieval task based on memory performance. In the retrieval task, brain imaging data are sorted for both emotional and neutral items according to whether they are remembered or forgotten.

Next brain imaging data associated with subsequently remembered and forgotten items are compared to each other to identify brain regions showing differences due to memory or DM effects. That is region showing greater activity for remembered than for forgotten items. If this comparison is based on brain imaging data recorded during encoding, it allows identification of brain regions associated with encoding success.

If on the other hand, this comparison is based on brain imaging data recorded during retrieval, it allows identification of brain regions associated with retrieval success, as we will see later, comparison of memory related activity for emotional and neutral items allows identification of brain regions that contribute to the memory enhancing effect of emotion Because it allows identification of the neuro correlates of the emotion effect on both general and memory specific processing. This method might contribute to better understanding of effective disorders such as depression and anxiety, where there are changes in both general emotion processing and emotional memory. The main advantage of this technique over existing methods like animal research or research performed on brain damage human patients is that it's not invasive and it allows specifically for the identification of the neural correlates of the memory enhancing effective emotion in the intact human brain.

Several aspects should be considered to successfully implement the subsequent memory paradigm with emotional stimuli in order to investigate the neural correlates of the memory enhancing effect of emotion. Foremost, the stimuli should be controlled on two major effective dimensions that define the emotional properties of A, these being emotional valence, the degree of unpleasantness or pleasantness and emotional arousal. The emotional intensity commonly used emotional stimuli for this task are pictures from the International Effective Picture System developed by the NIMH Center for Emotion and Attention at the University of Florida.

It is important to control for these emotional properties as they may have different effects on emotional perception and on emotional memory. Other factors whose manipulations may also affect memory performance and hence contribute to the versatility of this protocol include the type of learning during the encoding task, the type of emotional processing during encoding, and the type of retrieval task used. Other possible confounding variables such as the human presence in and visual complexity of emotional and neutral pictures should also be controlled for.

It is also important that the task is designed such that memory performance for the conditions of interest will result in roughly equal numbers of remembered and forgotten trials, so that fair statistical comparisons of both behavioral and brain imaging data can be made to investigate the neural correlates of the memory enhancing effect of emotion. It is also important that a memory advantage for emotional stimuli is obtained behaviorally. Finally, it is advised that the emotional stimuli are pseudo randomized to ensure that no more than two to three pictures of the same valence are consecutively presented.

This will ensure that induction of longer lasting emotional states is avoided. Here we see a sample of trial sequence from the encoding task. Please note that for the purpose of illustration, the timing of stimulus presentation is compressed compared to that of an actual experiment.

Have your subject arrive about an hour prior to the scanning session, and be sure to obtain written and informed consent from the participant as dictated by your institution's ethics or review board. Also screen for MRI safety and ask the subject to remove all metal that he or she may be wearing approximately 45 minutes. Before starting the scan, have the subject complete questionnaires to assess overall emotional state and anxiety level.

These initial assessments can later be used in combination with post session assessments to screen for changes in mood and anxiety as a result of participating in the study. Next, describe the details of the scanning procedures and give specific instructions for the behavioral task. Also, have him or her complete a short practice session to become familiar with the task and the button box.

Now bring the subject into the scanning room and instruct him or her to supine on the scanning bed. Provide ear protection as well as isolation headphones for communication during the scan. Additional cushioning for the head should be placed to ensure comfort during the scan and to minimize movement.

Also, the non-adhesive side of a length of tape may be wrapped lightly around the participant's forehead. To further minimize head movement, position the subject's right hand comfortably on the response box and check to make sure the buttons are working properly. Place an emergency stop button nearby so that the subject may indicate any urgent need to stop the scanner before starting data collection.

Ensure that the subject can clearly see the screen projection for stimulus presentation. To begin acquire a localizer and a high resolution to T one weighted structural image such as an SPGR or MP rage. In our experiment data were collected on a 1.5 Tesla.

Next, set up your functional runs using an echo echo planar imaging sequence with full brain coverage. We suggest using a TR of no longer than 3000 milliseconds to ensure proper temporal resolution of FMRI.Recordings. With this TR length, we suggest a TE of 40 milliseconds, a 64 by 64 millimeter field of view and 90 degree flip angle, and a 3.75 millimeter slice thickness.

Before beginning the first functional run, tell the participant that the task is about to begin and briefly remind him or her of the task instructions. Now be sure that the scan and behavioral paradigm begins synchronously. Once the scan is complete, help the subject out the scanner and perform any post scanning assessments, including questionnaires to assess state of mood and anxiety levels.

How well do you think you performed on the task? I save pretty well And if not, perform before the scanning session. Assessments of personality traits such as neuroticism and emotional arousable.

Now, if memory is tested soon after scanning, allow the subject to sit in a waiting area or perform a distracting task such as solving puzzles. Since a minimum delay of 20 minutes should occur between the encoding and retrieval tasks to maximize the effect of emotion on memory. After the delay, run the retrieval paradigm according to the established experimental protocol.

Recording of brain imaging data can also be performed during the retrieval task using the same scanning parameters. As for the encoding task, after scanning is complete, help the subject out of the scanner and obtain emotional ratings for the stimuli, which can be used to assess the subject's emotional responses to compliment the normative ratings of the stimuli. Once all scanning and questionnaires are complete, be sure to thank your subject for participating in the study and to provide compensation for his or her time.

Here we focus on analyzing the FMRI data recorded during encoding in order to isolate the memory enhancing effect of emotion. Once the data has been collected, it can be analyzed using any FMRI processing software package such as statistical parametric mapping or SPM. Our lab uses this in combination with in-house MATLAB based tools.

Typically, pre-processing of FMRI data involves the following steps, quality assurance, image alignment, motion correction, co-registration to a structural image, normalization, and spatial smoothing. When using SPM, the general linear model is implemented to assess the fit of the recorded data from each condition of interest to a predetermined hemodynamic response function. Alternatively, the data from each condition can be selectively averaged to view the raw MR signal associated with each condition with no predetermined assumptions about the shape of the hemodynamic response function.

Individual and group level statistical analysis can be performed involving comparisons of brain activity based on subsequent memory performance for the emotional and neutral stimuli, three main analyses are allowed by the subsequent memory paradigm. First comparison of activity for remembered and forgotten stimuli regardless of their emotional content allows identification of memory related brain activity. Second, comparison of brain activity for emotional and neutral stimuli independently of the subsequent memory.

Performance for those stimuli allows identification of brain activity linked to general emotion processing. Third, the most important analysis in the context of using the subsequent memory paradigm with emotional stimuli involves comparison of DM effects for emotional and neutral stimuli. In order to identify brain regions whose memory related activity is modulated by emotion, namely showing greater emotional than neutral DM effects.

This comparison allows identification of brain regions contributing to the memory enhancing effect of emotion. The effect of emotion or memory can be assessed in different ways depending on how the emotional properties of the emotional and neutral stimuli were manipulated. For instance, the use of highly arousing emotional stimuli to contrast with lower arousing and neutral stimuli has become a common manipulation in studies of emotional memory.

This comparison allows identification of arousal related effects of emotion on memory. Also, by comparing equally arousing positive and negative stimuli with each other, it is possible to identify valence related effects. Other manipulations that allow identification of valence related effects may involve comparisons of equally arousing emotional and neutral stimuli.

Another possible way of identifying arousal related effects is to compare the effects of high and low arousing stimuli within the same valence category. Also, valence related effects can be assessed by comparing all emotional stimuli regardless of arousal with the neutral stimuli. Ideally, it is best to use a full factorial design which manipulates arousal across all valence categories, negative, neutral, and positive.

Here we present findings from a study looking for evidence supporting the modulation hypothesis. According to this hypothesis, emotion enhances memory through modulatory influences from the amygdala and emotion processing region on activity in medial temporal lobe memory regions consisting of the hippocampus and the associated para hippocampal cortices to identify the specific contribution of these neighboring regions to the memory enhancing effect of emotion. The study employed the so-called anatomical regions of interest method that involved extraction of FMRI signal from ROIs that were manually traced on brain images in each participant's data.

Here we see a 3D view of these regions as well as 2D images with their actual location. In the brain, imaging data from a representative subject first behavioral data showed that memory was better for emotional than for neutral pictures with no difference between positive and negative pictures because the positive and negative pictures were equally arousing and more arousing than the neutral pictures. This suggests that the difference in memory performance was driven by arousal.

Thus, the analysis of brain imaging data focused on identifying brain activity paralleling this behavioral pattern by collapsing the data for positive and negative pictures into an emotional category. Here to the left, we see bar graphs showing greater encoding success activity or DM effects for the emotional than for the neutral pictures in both the amygdala and the MTL memory regions. Moreover, consistent with the idea that these regions interact with each other during the formation of emotional memory.

Encoding success activity in these regions was more strongly correlated for emotional than for neutral pictures as shown by the scattergrams at the right side of the screen. These findings provide strong evidence for the modulation hypothesis from neurologically intact human participants. While performing this procedure, it's important to remember to consider the various factors that must be taken into account in order to successfully implement the subsequent memory paradigm with emotional stimuli.

After watching this video, you should have a good understanding of how to successfully implement the subsequent memory paradigm to investigate the neuro correlates of the memory enhancing effect of emotion.