First, consistent with the notion that gratitude motivates increased attunement toward rewards to others versus the self, we tested the prediction that self-report measures of gratitude are related to self-report measures of altruism and behavioral responses to charitable donations versus self-gains. We also tested the degree to which they may be represented as a single construct that predicts neural pure altruism, operationalized as activity in reward-related brain regions while subjects privately observe mandatory money transfers to a charity or to themselves.
We chose to focus on this measure because it cannot be interpreted in terms of impure altruistic motives e. Also, the neural pure altruism measure is not subject to the validity threats that plague self-report measures or giving that is not private. Therefore, it provides a particularly stringent test of our individual differences hypothesis that gratitude relates to a pure form of altruism.
As a second hypothesis, we tested whether gratitude practice increases our neural measure of pure altruism, consistent with the view of gratitude as a moral and expressive emotion. More specifically, we used random-assignment and a double-blind design to assign participants to either 3 weeks of gratitude journaling or an active control journaling condition.
Then we compared pre- and post-test levels of neural pure altruism between groups.
MRI: A conceptual overview.
Here, the neural measure allows us to test the idea that gratitude practice enhances responses that benefit others versus gains to oneself, specifically interrogating the neural system implicated in flexible determination of value Clithero and Rangel, All participants gave informed consent, all procedures were approved by the University of Oregon institutional review board and were in accord with the Declaration of Helsinki. Participants were recruited from the psychology undergraduate e-mail list at the University of Oregon and prescreened to ensure they were healthy, without MRI contraindications, right-handed, ages 18—35 years, not taking psychoactive medications, had no history of neurological or psychiatric conditions, and were willing to participate in a 3-week journaling study.
All learned English as their first language and were currently living in the United States. Three participants randomly assigned to the gratitude group were lost due to attrition before the second MRI session one informed us of an acute health issue, one informed us she was too busy to journal, and one did not complete regular journal entries and was informed she could no longer participate. None reported that they wished to withdraw due to the content of the journal entries.
The final sample of participants who completed post-testing was 33 people ages 18—27 years, 16 in the Gratitude group and 17 in the Active-Neutral group Table 1.
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We were limited by resources to this sample size, so only female participants were recruited for these experiments since gender differences in gratitude, giving behavior and neural responses to affective stimuli could increase variability Meletti et al. A larger sample size would more accurately estimate the magnitude of the effects see Ingre, and allow for tests of gender differences.
Participants completed a battery of online questionnaires, detailed below, the day before the first MRI scanning appointment MRI Session 1. At Session 1 participants were shown a slide presentation with task instructions and information about the mission of a charity a local food-bank and then they practiced the tasks in a mock scanner.
In the MRI scanner, participants completed two runs of the giving task detailed below followed by the anatomical scan. They also completed a task where everyday social vignettes were rated to be reported in a separate article.
Participants were blind to the aims, hypotheses, conditions, and design of the current experiment. All research-staff interacting with participants were blind to group assignment and journal content. Two cohorts were recruited, in Fall and Winter term, with testing scheduled according to the quarterly academic calendar so that post-testing at Session 2 could be completed at least 2 weeks prior to final exams.
Participants were paid their task-bonus and made their donation after completion of Session 1. The main domains of interest were gratitude and altruism so our planned analysis focuses on the GQ-6 gratitude questionnaire assessing the propensity to experience gratitude in daily life McCullough et al. These two measures were acquired within in a longer battery of questionnaires.
The day after MRI Session 1, participants were randomly assigned to one of two journaling conditions Gratitude or Active-Neutral and sent a link to a secure online portal Qualtrics. Participants were instructed to write at least a min journal entry every evening between dinner and bedtime for 2—3 weeks until their next MRI scanning appointment Session 2. We checked daily whether journal entries were completed, but did not check the contents of the entries, and we reminded participants the evening following a missed journal.
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On average, the Gratitude group completed 16 entries over 19 days, and the Active-Neutral group completed 18 journal entries over Compliance and time between pre- and post-test did not differ between groups Table 2. For the active-neutral group, we designed the prompts to be engaging without a focus on gratitude Table 3. Upon submission, the entry was displayed and participants indicated which prompt they had chosen and rated how they felt about their entry on a 7-point Likert scale from very unhappy to very happy. Finally, a flower name was displayed from a randomized list of common flower names e.
Prompts from either the Gratitude or Active-Neutral columns, depending on group assignment, were displayed to participants each time they logged in to the online portal. The day before Session 2, participants completed online questionnaires identical to Session 1 except without demographic questions.
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At Session 2, participants were informed in writing by imaging-center staff unaffiliated with the study that researchers had not read any journal entries and participants were asked not to mention their journal contents until debriefing. MRI Session 2 had the same tasks as Session 1. At debriefing, we told participants about the aims of the study and all were given information on the potential benefits of gratitude journaling. We modified a charitable giving task based on previous work Harbaugh et al. Passive transfers selected by the computer are used for the pure altruism contrast, charity-gain minus self-gain.
Great care was taken to ensure that participants understood that experimenters were not monitoring their choices, that one mandatory and one voluntary transfer would be implemented at random, and that no deception would occur. A , top panel Shows the possible trial types.
C , lower panel Shows the rating screen for mandatory transfers and the rating screen for voluntary transfers. Each run of the task, two per session, consisted of 84 trials for a total duration of approximately 10 min per run. Runs were not self-paced, and each event within each trial was jittered. A new trial began with the fixation-cross. After the participants exited the scanner, the lottery was implemented and they were paid in cash and given a receipt for their donation to charity.
Participants had ample time to encode the transfer and make a decision prior to the display of the rating screen so response times were not analyzed. The main dependent behavioral variable was the satisfaction ratings for mandatory transfers representing the majority of the trials. The critical tests were as follows: First, whether transfer ratings, self-reported gratitude, and self-reported altruism would be related to the neural reward system response to the pure altruism contrast at Session 1. Next, these behavioral and self-report measures were combined into aggregate variables as potential behavioral proxies of general benevolence Hubbard et al.
Third, we examined whether gratitude practice changed neural pure altruism from pre-test to post-test. Specifically, we expected that we would observe an increased response in reward-related regions, particularly the VMPFC, for charity-gains versus self-gains in line with the view that gratitude increases pure altruism.
Imaging data were acquired using a Siemens Skyra 3. Functional and anatomical brain image slices were prescribed in the mid-sagittal plane along the anterior commissure-posterior commissure AC-PC transverse oblique plane. For whole-brain functional images: Foam pads minimized head movement, earplugs were worn to protect hearing, and headphones were used for communication.
A response box collected button presses from the dominant hand. We monitored alertness via a camera fixed on the right eye. For each participant, functional volumes were realigned to the first image in the series. The anatomical image was registered to the realigned functional images, and reorientation parameters were manually derived and applied to all images to set the origin above and behind the anterior commissure.
Anatomical images were segmented Ashburner and Friston, and deformations fields from this transformation were used to warp functional images into standard space MNI ICBM template at 2 mm isotropic resolution. Finally, functional images were smoothed with a 6 mm FWHM smoothing kernel. We used Pythagorean distance to derive four motion parameters for each volume rotation, translation, and first derivative of rotation and translation as regressors of no interest in the general linear model. Condition effects were estimated according to a general linear model in SPM12 using a canonical hemodynamic response function, high-pass filtering s , correction for temporal autocorrelation auto-regressive model; AR1 , and a subject specific explicit mask.
These individual subject masks were averaged and re-binarized to create an explicit mask for use in random-effects, group-level analyses. Four Pythagorean motion parameters derived from the six SPM motion parameters in the realignment procedure were added to the model as regressors of no interest. Regressors for each of the four runs two at pre-test, two at post-test were added to the model to allow for comparisons between Session 1 and Session 2.
Responses were not explicitly modeled as nuisance regressors since all conditions contained the same responses. Planned linear contrasts were created for the main contrast of interest charity-gain versus self-gain and for each condition compared to implicit resting baseline at Session 1 and for the difference between Session 2 and Session 1.
These contrasts were then entered into a random-effects group model to estimate population effects. Analyses focused on individual differences comparisons at pre-test to test hypothesis 1, using self-report and behavioral measures as regressors of interest. To test hypothesis 2, analyses focused on the contrast indexing change in pure altruism from pre- to post-test. For these main statistical analyses, mean parameter estimates across voxels were extracted from ROIs for the pure altruism contrast charity-gain greater than self-gain.
We selected ROIs that are consistently implicated in subjective value: An aggregate neural variable, the mean parameter estimate across all ROIs, was calculated as a proxy for the Neural Utility modeled in previous work Hubbard et al. We also focused on a VMPFC aggregate in our tests of intervention effects since previous studies found associations between gratitude and regions in the medial prefrontal cortex Fox et al. Finally, we conducted exploratory whole-brain analyses to investigate the extent of potential coactivation with other neural systems.
First, we tested the extent to which self-reported gratitude was associated with self-report and behavioral measures of altruism at Session 1. Scatterplots of these relationships are provided in Supplementary Figure S1. Overall, these analyses support the hypothesis that gratitude is related to increased altruistic tendencies, and that these individual differences are supported by value-sensitive regions that have been implicated in previous studies Harbaugh et al.
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We were also interested in whether an aggregate of the non-neural, behavioral benevolence measures was related to an aggregate of the neural measure of pure altruism, treating gratitude as part of a prosocial disposition that supports altruism, relying on a network of value-sensitive regions indexing utility. First, we created an aggregate variable incorporating self-reported gratitude, self-reported altruism, and satisfaction ratings for costly donations.
Next we created an aggregate from the seven cortical and subcortical neural ROIs as a proxy of the neural utility measure across reward system regions reported previously by Hubbard et al. The motivation for this analysis was to reduce the number of comparisons required to relate the behavior to neural activity. As noted in the methods, medial prefrontal activity has been implicated in previous neuroimaging studies of gratitude, so separately we focused on the VMPFC ROIs.
Finally, as the main analysis of interest, we examined the relationship between the behavioral and neural aggregates Figure 2 and Table 4: This suggests that gratitude contributes to a general prosocial disposition that supports giving, and that it is expressed in the context of pure altruism via value-sensitive brain regions, most robustly in the VMPFC. Linear relationship between the behavioral benevolence aggregate and aggregates for neural pure altruism in seven a priori regions of interest ROIs implicated in previous research Hubbard et al.
This also explains why some motion contrast are disproportionally better at higher field strengths e. T2 and tissue type T2 refers to the how rapidly nuclei fall out of phase transverse relaxation. T2 relaxation is directly related to the delay between when we transmit a radio-pulse to the time when we record the radio signal being emitted the echo time, TE.
Since nuclei spin faster at higher field strengths, they tend to fall out of phase more rapidly. This is one reason why TEs are often faster for higher field strengths. Likewise, hydrogen T2 varies with tissue type. This image shows the T2 effects for several different tissue types. Human Brain Mapp ;9: Dynamics of blood Flow and oxygenation changes during brain activation: Biphasic hemodynamic responses influence deactivation and may mask activation in block-design fMRI paradigms.
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