שימוש ב- fMRI כדי לנתח שיפוט מוסרי

Deciding whether something is right or wrong doesn’t just involve an emotional drive. Sometimes, moral judgments are based on reason.

For instance, in the classic trolley dilemma, most individuals say that they would pull a switch to stop a train from hitting five people by diverting it and killing one person.

However, in another case—the footbridge dilemma—most individuals would not push a large man off of a bridge to hit a train that would kill him, even though that would stop the train from running into five other people.

In both situations, reason would dictate that one life should be sacrificed to save five. Although to many, pushing the man feels wrong—it triggers more negative emotions than simply pulling a switch.

This video demonstrates how to integrate moral dilemmas into an experiment—using functional magnetic resonance imaging, fMRI—to analyze the neural underpinnings associated with the use of reason and emotion based on previous work of Greene and colleagues.

In this experiment, participants undergo a brain scan using fMRI while they are presented with 30 scenarios—involving personal, impersonal, and non-moral decisions—written in text format on a presentation screen.

The first type—a personal moral dilemma—involves the participant imagining to perform an action that directly harms one person in the service of some goal, like harvesting the organs of a person to save several other people.

The second category—impersonal moral questions—involves the participant imagining to perform an action that indirectly harms one person in the act of a goal, such as stealing a boat to save people during a hurricane.

The final kind—a non-moral situation—involves the participant imagining to perform an action that is not typically viewed in moral terms at all, like deciding whether to travel by plane or train given a limited about of time.

All are shown across a series of three screens, in which the first two display text describing the dilemma and the last asks a question whether the action is appropriate or inappropriate. This format allows better segmentation of the neural response with the decision-making processes.

Within each vignette, baseline activity is defined as the mean signal across the last four scans of the inter-trial interval. And, task-related activity is measured using a floating window of eight scans, meaning four will be obtained before, one during, and three after the response to the final question in each trial.

In this case, the dependent variable is the percent change in brain activity during baseline compared to the activity during participants’ moral judgments during the 3rd screen of each dilemma.

The brain areas associated with emotion—the medial frontal gyrus, posterior cingulate gyrus, and angular gyrus—are predicted to be significantly more active when participants make judgments about personal dilemmas compared to impersonal ones, which rely more on reasoning processes associated with the middle frontal gyrus and the parietal lobe.

Prior to the experiment, conduct a power analysis to recruit a sufficient number of healthy participants. Also, verify that the previously created dilemma stimuli will appear correctly on the presentation computer.

On the day of the scan, greet the participant and ensure that they do not suffer from claustrophobia or have any metal in their body. Have them fill out the necessary consent forms detailing the risks and benefits of the study.

After they are signed, explain to the participant that they will see three screens with text on it for every scenario, and that they must click the button box to advance through each screen. Then, tell them to answer the question on the 3rd screen by pressing one of two buttons to indicate either "appropriate" or "inappropriate".

Next, prepare the participant to enter into the 3T scanning room. For more detailed information on the pre-scan procedures, please refer to another MRI project in JoVE’s SciEd Neuropsychology collection.

With the participant now in the bore holding the MRI safe button box in their hand, begin imaging and display the dilemma stimuli on the screen in the scanner, and include an inter-trial interval of 14 s.

During the session, acquire functional images in 22 axial slices with the following parameters: an echoplanar pulse sequence, TR of 2000 ms; TE of 25 ms; flip angle of 90°; FOV of 192 mm; 3.0-mm isotropic voxels; and 1-mm inter-slice spacing.

After 30 dilemmas have been presented, escort the participant out of the scanner, and debrief them to conclude the study.

Prior to statistical analyses, co-register images for all participants using a 12-parameter automatic algorithm and smooth with an 8-mm, full width at half maximum, 3D Gaussian filter.

Then, to assess brain activity during task performance, analyze the images contained in each response window using a voxel-wise mixed-effects analysis of variance, with participant as a random effect, and dilemma-type, block, and response-relative image as fixed effects.

Threshold maps of voxel-wise F-ratios for statistical significance and a cluster size of 8 voxels. Likewise, threshold the planned comparisons for significant differences between conditions.

Finally, measure the percentage change, relative to the baseline, in brain activity for each of the crucial brain areas related to either reason or emotion processing.

Plot these values across brain regions, separating those associated with emotion and reason.

Notice that the medial frontal gyrus—an area previously linked with emotion—was significantly more active when participants made judgments about personal dilemmas compared to when they made judgments about impersonal ones. This effect held true for the other emotion areas as well.

Interestingly, for impersonal scenarios, brain areas previously linked with reasoning were significantly more active than when considering personal dilemmas. These results provide evidence for just how powerful the psychological processes of emotion and reasoning are when making moral judgments.

Now that you are familiar with how to design a moral judgment task integrated with functional neuroimaging, let’s look how researchers apply emotion and reasoning to study morality in other populations, including psychopathy and politics.

Psychopaths often appear perfectly intelligent—with intact reasoning—yet they are capable of performing immoral acts such as murder.

Based on the findings discussed previously, this abnormal population more than likely lacks the emotional response telling their brain that what they are doing is wrong when committing an immoral act. Therefore, they may benefit from therapy that focuses on fostering specific emotions toward certain immoral actions.

Furthermore, given that political divides are often very personal and are driven by differences in moral views, this research exemplifies that political differences are often propelled by emotions. Thus, individuals are more likely to be unresponsive to reasonable arguments from an opposing party. Emotions are indeed a force to be reckoned with!

You’ve just watched JoVE’s video on investigating moral judgments and the neural correlates using fMRI. Now you should have a good understanding of how to design and conduct an experiment involving different decision-making scenarios, as well as how to analyze and interpret brain activity and psychological implications related to the role of emotion and reason in moral situations.

Thanks for watching!