The overall goal of this experimental protocol is to investigate the neural correlates of the detrimental impact of emotion on cognition with a focus on working memory processes. This is achieved by recording brain activity using FMRI, while participants perform a working memory task with emotional distraction presented during the delay interval between the memoranda and probes following the creation of the basic working memory task, distracters are selected according to the goals of the investigation and targeted populations. For instance, if no specific emotions are targeted, emotional stimuli inducing general emotional responses, positive or negative can be employed.
Whereas if the effects of specific emotions such as fear are targeted, fear inducing distractions may be used either in healthy or in clinical participants. Next, behavioral and brain imaging data collected while participants perform the working memory task with distraction are analyzed in order to identify differential effects of emotional distraction on working memory performance and the associated neural correlates results are obtained that show patterns of brain activity linked to a detrimental effect of emotional distraction on working memory performance, as well as brain activity associated with the ability to cope with emotional distraction. Typical targeted brain regions include areas that are associated with the ability to stay focused, which are part of a so-called dorsal executive neural system here illustrated in blue, and regions that are involved in motion processing, which are part of a ventral effective system illustrated in red.
The implications of this technique extend toward understanding and possibly diagnosing anxiety disorders such as post-traumatic stress disorder because it allows identification of changes associated with dysfunctional responses to emotional distraction. Well, the main advantage of this technique over existing methods like those involving the simultaneous presentation of goal relevant information and task irrelevant emotional distraction, is that allows us to better separate the neural correlates in response to emotional distraction from those associated with ongoing cognitive processes. Moreover, this paradigm not only allows us to investigate the neuro correlates of cognitive interference, but also the neuro responses of coping with emotional distraction.
The basic task of this protocol is a delayed response working memory task in which novel emotional and non-emotional stimuli are presented as task irrelevant distractors during the delay interval between the memoranda and probes. Scrambled versions with identical basic properties such as spatial frequency and luminance to those of the actual distractors can be used as perceptual controls. Alternatively, trials with no distraction can also be used as basic controls.
It should be noted that the emotional and non-emotional distractors should be used in different trials. Also, to increase the impact, it is recommended to pair distractors with similar emotional and semantic properties. Emotional and neutral distractors in the original design just seen can be selected from the international effective picture system, but similar effects can be obtained with other novel stimuli that are effective as distractors.
For instance, faces displaying angry expressions could induce specific emotional responses such as social anxiety, and thus could be effective in investigating the impact of transient anxiety inducing distraction on working memory. Similarly, in clinical participants such as post-traumatic stress disorder patients, the specificity of distraction could be increased by presenting trauma related stimuli. For example, using combat related pictures in war veterans with PTSD.
If anxiety inducing facial stimuli are used to increase the impact, we suggest morphing them as seen here, rather than presenting the faces as static images. Using your chosen stimulation presentation software set up this task as an event related design with three faces in the working memory task, followed by novel distractors. Participants should be instructed to maintain their focus on the meran while still processing the distractors and to make quick and accurate responses to the single face probes by pressing a response button, one indicating old or remembered, and two, indicating new additionally manipulations that increase the sensitivity of the working memory task In detecting behavioral differences such as assessing the participant's confidence in their responses can also be implemented.
Note that for illustration purposes, this example does not involve the real timing of the task. Finally, the difficulty of the working memory task can be varied by manipulating the presence of color and or extra facial features in the memoranda, as well as the similarity of the faces when the subject arrives. Be sure to obtain written and informed consent and to screen for MRI safety.
Also assess for present emotional state as well as personality traits such as anxiety and emotional reactivity. I'd like for you to complete a few questionnaires assessing your current emotional state. Okay, It should take about 10 minutes Prior to the scan.
Inform the participant in detail of the scan procedures and give specific instructions for the behavioral task to avoid discomfort and to create increased familiarity with the task. Also, give the participant an abbreviated practice run. Now bring the subject into the scanning room and instruct him or her to lie supine on the scanning bed.
Provide ear protection as well as isolation headphones for communication during the scan place additional cushioning around the head 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 ensure that the response buttons work properly.
Place an emergency stop button nearby so that the subject may indicate any urgent need to stop the scanner, and finally, make sure that the subject can see the screen projection clearly for stimulus presentation before sending him or her into the scanner. Now acquire a high resolution T one weighted structural image such as an SPGR or MP rage. Next, set up your functional runs to allow full brain coverage.
In our initial studies using a four Tesla scanner, we acquired axial series of 30 functional slices with a four by four by four millimeter voxel size, using an inverse spiral pulse sequence with the following parameters, a TR of 2000 milliseconds, a TE of 31 milliseconds, and a field view of 256 by 256 millimeters. More recently, we also adapted the paradigm for a 1.5 Tesla scanner using the following parameters, 28 functional slices with a four by four by four millimeter voxel size acquired axially using an Echo Plano sequence and using a TR of 2000 milliseconds, a tea of 40 milliseconds and a field of view of 256 by 256 millimeters inform the subject that the functional imaging is about to begin and remind him or her of the tasks now start the scanner synchronously with the paradigm when scanning is complete, help the subject out of the scanner and perform a behavioral assessment to determine the participant's sensitivity to the distractors by rating the emotional intensity of the distractors and the subjectively perceived distractibility of the distractors. Individual differences in those ratings can be used to investigate their influence on the neural mechanisms, mediating the detrimental effect of emotion on cognition or to identify brain regions involved in coping with emotional distraction.
Finally, be sure to thank the subject for participating in the experiment. Once collected, data can be analyzed using any FMRI processing software package, such as statistical parametric mapping, commonly known as SPM. Our lab uses this in combination with in-house MATLAB based tools.
Pre-processing involves typical steps, quality assurance, image alignment, motion correction, co-registration, normalization, and spatial smoothing with an eight millimeter kernel. 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 FMR signal associated with each condition with no predetermined assumptions about the shape of the hemodynamic response function.
Contrasts of interest then reveal changes compared to pre stimulus, baseline, and differences between one condition when compared to another condition. With this experimental protocol, we suggest using analysis tools that allow assessments of changes in the FMR signal on a time point by time point basis, individual and group level Statistical analysis involve comparisons of brain activity according to the distractor type. Moreover, correlations of brain imaging data with subjective or objective measures of distractability and scores indexing.
Personality measures can also be performed to investigate how brain activity covar with individual differences in those measures. Here we illustrate the basic procedure for identifying brain behavior relationships using across subject correlations between brain activity and subjective ratings of distractibility. First, individual scores of distractibility are calculated for each subject.
Secondly, their correlations with changes in brain activity are calculated either on a voxel by voxel basis or with FMR signal extracted from specific regions of interest or ROIs. Third scattergrams of these correlations are then plotted analyses in all of our studies using this protocol have typically involved assessments of changes in the FMR signal observed during the delay interval when the distractors are presented, but activity time locked to other events such as the probes can also be investigated. Here we illustrate the main findings from our initial study using emotional and neutral distractors selected from the International Effective Picture System.
The central panel shows activation maps of the direct contrast between the most versus the least distracting conditions superimposed on a high resolution brain image displayed in a lateral view of the right hemisphere. The focus is on activity recorded during the delay interval when the distractors were presented. Activity in the dorsal executive neural system is shown in blue, and activity in the ventral effective system is shown in red.
The color horizontal bars at the bottom of the brain image indicate the gradient of T values of the activation maps. The lateral panels illustrate time courses of changes in brain activity during the working memory task with distraction with the upper panels showing activity in dorsal executive regions such as the dorsal lateral prefrontal cortex and lateral parietal cortex, and the lower panels showing activity in regions of the ventral effective system such as the ventral lateral prefrontal cortex or region susceptible to effective modulation such as the fusiform gyrus. The time courses in blue represent the scrambled meaningless distractor while the time courses in red indicate the emotional distractor and the time courses in yellow represent the neutral distractor in the presence of meaningless distraction.
Sustained activity occurred in regions of the dorsal executive system. The presence of emotional distraction increased activity in regions of the ventral effect system, while decreasing activity in the dorsal system and impairing working memory performance paralleling the behavioral impact, the presence of neutral distractors produced an intermediate level of activity in both systems. This dorso ventral dissociation has been systematically replicated and was shown to be specific to emotional distraction.
This experimental paradigm also allows identification of brain regions involved in coping with emotional distraction. For instance, correlation analyses between activity in brain regions sensitive to the presence of emotional distraction identified areas in the ventral lateral prefrontal cortex whose activity correlated negatively with indices of emotional distractibility for the emotional, but not for the neutral distractors. Specifically, participants showing greater activity in this region also perceived and rated emotional distractors as less distracting.
These findings provide evidence for a role of this region in coping with distracting emotions. After the development of this paradigm, it paved the way for researchers in the field of emotion and cognition interactions to study the neuro correlates of both responding to and coping with emotional distraction in both healthy and clinical populations. After watching this video, you should have a good understanding of how to use this protocol to investigate the neuro correlates of cognitive interference by emotional distraction and how to adapt it to your own experimental needs.
