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Different Strokes for Different Folks: Exploring How Personality Modulates Response to Gift-Receipt

NEUR 494 Honors Thesis Gurleen Chadha

PI: Lisa Aziz-Zadeh Glenn R. Fox May 13, 2015

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Abstract: The act of exchanging gifts, whether those gifts are tangible objects or favors, is an essential component of everyday life. Ideally we hope that these gifts elicit gratitude, but we also know that different people process gifts in different ways. In this exploratory study, we examine i) the correlations between personality and brain activity during gift-receipt and ii) the interaction between personality and gratitude-modulated brain activity during gift-receipt. When analyzing brain activity while receiving a gift, we found that agreeableness was negatively correlated with brain activity in the left medial prefrontal cortex, right subgenual anterior cingulate cortex, and left temporal pole. Conscientiousness was positively correlated with brain activity in the left posterior insula. Analysis of gratitude-modulated brain activity during gift-receipt revealed that openness to experience was negatively correlated with gratitude-modulated brain activity in the right posteromedial cortex (superior and inferior) and the left secondary somatosensory cortex. Neuroticism was positively correlated with gratitude-modulated brain activity in the right anterior insula and bilaterally in the superior regions of the posteromedial cortex. The data suggest that gift-receipt invokes neural circuitry for an emotion-processing system and regions associated with the default mode network. The degree to which these circuits are active is modulated by personality, and may explain why different people react to gifts in different ways.

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Introduction: As a component of daily life, the act of gift-giving plays a critical role in how we relate to others and how we perceive others’ feelings about us. However, while it is clear that individual differences play a role in how gifts are perceived, it is unclear how these differences play out at the level of the brain. This investigation focused on two primary questions: i) how personality modulates the response of receiving gifts in general and ii) how personality modulates brain responses during the experience of gratitude. In the scientific literature, gratitude is typically defined in two ways: i) as the emotion that occurs after people receive aid or support due to the good intentions of another person and ii) as a trait of personality (Wood et al., 2010; Emmons & Stern, 2013). This investigation focuses on the former definition, of gratitude as a feeling, and seeks to understand how personality traits affect brain activity when experiencing gratitude. Previous research has shown that gratitude is a trait associated with numerous positive benefits, including a quicker recovery from physical illness, better coping with stress, and better physical health (Emmons & Stern, 2013). Studies examining gratitude and personality have found positive correlations between gratitude and agreeableness, extraversion, openness, and conscientiousness, though not every study has found a correlation between gratitude and the four traits (Wood et al., 2010). However, while there has been research done on the neural correlates of emotional personality during positive experiences, none of these studies have investigated gratitude. This is unfortunate, because the literature clearly shows that clinical disorders including bulimia, alcoholism, and PTSD are strongly tied to personality traits, most often neuroticism (Kendler et al., 1991; Ralevski et al., 2010; Breslau & Schultz, 2013) and it just as clearly shows that gratitude serves as a protective agent against these very same disorders (Wood, et al., 2010; Emmons & Stern 2010). What’s more, very few studies have examined the intersection between health and personality at the level of the brain. Learning about the intersection of personality and gratitude in specific regions of the brain can potentially help us in two ways: first, we can better understand how these disorders affect brain activity, and second, we can potentially track the effectiveness of ongoing treatment for these disorders. In this investigation, we use functional brain imaging to analyze i) how personality modulates the neural processing associated with receiving a gift, and ii) how the experience of gratitude is modulated by personality. In regards to the current literature on brain imaging and personality, Koelsch et al. (2013) provide an overview of the current research on these functional associations. They find agreeableness associated with activity in the ventral striatum, orbitofrontal cortex, cerebellum, cingulate cortex, and the dorsolateral prefrontal cortex; extraversion associated with activity in the cingulate cortex, striatum, and prefrontal cortex; and neuroticism associated with activity in the cingulate cortex, amygdala, insula, and prefrontal cortex. No functional data was available for the factors openness to experience and conscientiousness.

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The link between personality and gratitude has been quite understudied, although Wood et al. (2010) links gratitude to high extraversion, agreeableness, conscientiousness, and openness to experience, and low neuroticism. However, these associations are not always replicated in subsequent reports (Wood et al., 2010; Senf & Liau, 2014). To examine how personality modulates the brain i) during gift-receipt and ii) as a function of gratitude, we performed a region of interest (ROI) analysis. We focused on activity in brain regions known to be modulated by perspective-taking or personality traits, such as the medial prefrontal cortex, insula, and temporal pole (Wood, et al. 2010; Koelsch et al., 2013). We expected that regions previously found to be connected with positive affect should be active while experiencing gratitude (through gift-receipt) while regions associated with negative affect should not be active under the same experience. Methods: Participants: Data was collected from 23 participants (12 female), with an average age of 21 (min = 18, max = 28, sd = 2.21). All participants gave written, informed consent as approved by USC’s Institutional Review Board. All participants were right-handed native English speakers. Experimental Procedure: The design of the experiment focused on immersing the participants in the tragedy of the Holocaust, and having them experience for themselves a number of scenarios. To accomplish this, the experiment was designed to mimic a visit to the United States Holocaust museum, in which visitors experience each of the four historical phases of the Holocaust. As such, fMRI scanning was done via a slow event-related design in which participants viewed 48 scenarios, divided into four runs, each dedicated to a different phase of the Holocaust, consisting of 12 stimuli each.

In the scanner, participants began each phase by viewing a homemade documentary detailing the events of that phase of the Holocaust before being asked to experience a set of gift-based stimuli. We measured their reactions to the stimuli using their brain’s blood oxygenation level dependent (BOLD) signal activity.

Stimulus Design: Stimuli were derived from stories given by Holocaust survivors, which were drawn from the USC Shoah Foundation Institute’s Visual History Archive. The four runs corresponded with the four phases of the Holocaust, and each run was preceded by a two-minute video that documented the events from that phase of the Holocaust. The stimulus consisted of an approximately 30-word story in which a Holocaust survivor received a gift from another person. The participants were instructed to picture themselves as

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Holocaust survivors and the gift recipients; accordingly, each story was phrased in the first person. The framing of the story as first person and the decision to draw the stimuli from real Holocaust survivor testimony was intended to elicit the strongest possible emotional reaction.

Stimulus protocol: The stimulus appeared for ten seconds and was followed by a blank light blue screen, cueing participants to reflect on the gift and to feel as they would have felt had the gift exchange just occurred. The reflection period lasted for 12 seconds, after which participants were instructed to rate their gratitude on a scale of 1 to 4, with four being the maximum amount of gratitude. At the end of the trial, participants were shown a fixation cross and told to rest and to clear their thoughts of the previous stimuli. The time given for the rest condition averaged 12 seconds and was a normally distributed jittered range of values from 8 to 16 seconds. (See Figure 1). Following completion of the fourth run, participants were disconnected from psychophysiology equipment and asked to go through the stimuli once more, this time rating their gratitude for each gift on a scale of 1 to 9, with nine being the highest amount of gratitude. Figure 1: fMRI stimuli presentation paradigm.

This sequence was repeated 12 times per run, for a total of 4 runs. Psychometric Measures:

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After completing the experiment, participants filled out several behavioral questionnaires, including the Big Five Inventory, used to assess personality traits of extraversion, neuroticism, openness, conscientiousness, and agreeableness. Image Acquisition: Brain imaging was performed by Glenn Fox at the Dana and David Dornsife Cognitive Neuroscience Imaging Center at USC. Functional and structural magnetic resonance imaging (MRI) was employed using a Siemens 3T scanner. Four functional runs, one anatomical MPRAGE, and one T2 weighted image was acquired for each subject. Prior to performing the functional scans, structural images were collected in radiological convention with 176 slices, dimensions: 224 × 256 × 176 and then resampled with voxel dimensions 1 × 1 × 1 mm, TR 1950 ms. For functional scans, 250 volumes were acquired, with 37 slices per volume. The TR used was 2000 ms, with an interslice time of 54 and a TE of 30 ms. Inplane resolution was 64 × 64. Voxel resolution was 3.5 × 3.5 × 3.5mm, with no slice gap, the flip angle was 90◦. Data Analysis: Brain imaging data were analyzed by Glenn Fox using FSL (Smith, et al., 2010). FMRI data processing was carried out using FEAT (FMRI Expert Analysis Tool), part of FSL (FMRIB’s Software Library, www.fmrib.ox.ac.uk/fsl). Registration to high resolution structural and/or standard space images was carried out using FLIRT (Jenkinson and Smith, 2001; Jenkinson et al., 2002). The following pre-statistics processing was applied; motion correction using MCFLIRT (Jenkinson et al., 2002); slice-timing correction using Fourier-space time-series phase-shifting; non-brain removal was done using BET (Smith, 2002); spatial smoothing using a Gaussian kernel of FWHM 5.0mm; grand-mean intensity normalization of the entire 4D dataset by a single multiplicative factor; highpass temporal filtering (Gaussian-weighted least-squares straight line fitting, with sigma=50.0s). To determine the impact of personality on gift-receipt in the brain, activity in previously determined regions of interest (ROIs) was assessed in relation to each personality trait. Brain activity was measured using the beta value parameter estimate of the regions blood oxygenation level dependent (BOLD) signal in each ROI, averaged across all the voxels in the ROI. Participant scores on each personality trait were regressed with two aspects of activity: first, to examine how personality modulates reactions to gifts in general, ROI beta values were correlated with brain activity during the reflection stage of the experiment. Then, to examine how personality modulates the experience of gratitude itself, the beta values were correlated with brain activity during the reflection stage as modulated by gratitude ratings of the gifts. Regressions were carried out using RStudio and a significance level of p < 0.05 was used in accordance with previous literature (Acevedo

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et al., 2014; Cauda et al., 2010; Jackson et al., 2006; Jenkins & Mitchell, 2011; Koelsch et al., 2013). Results: Participant scores on each of the five factors were correlated with brain activity during the reflection period of the task. Agreeableness was found to be negatively correlated with activity in the right ACC (p=0.0338, R2=0.1588), left temporal pole (p=0.0171, R2=0.2061), and left medial prefrontal cortex (p=0.0053, R2=0.283). Conscientiousness was found to be positively correlated with activity in the left posterior insula (p=0.0470, R2=0.1357). No other significant correlations were found. (See Figures 2 and 3). We then correlated participant scores on each of the five traits with activity in ROIs as modulated by gratitude ratings. Openness was found to be negatively correlated with left secondary somatosensory cortex (p=0.0332, R2=0.1601), right inferior posteromedial cortex (p=0.01228, R2=0.2282), and right superior posteromedial cortex (p=0.0330, R2=0.1606). Neuroticism was found to be positively correlated with right anterior insula (p=0.0391, R2=0.1486) and bilaterally with right posteromedial cortex (p=0.0288, R2=0.1702) and left posteromedial cortex (p=0.0486, R2=0.1334). (See Figures 4 and 5). Results are summarized in Table 1.

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Figure 2: Summary of Brain Activity in Regions Modulated by Agreeableness

A scatterplot with regression line and R2 value in each of the areas that was associated (all negatively) with agreeableness.

Figure 3: Summary of Brain Activity in the Left Posterior Insula as Modulated by Conscientiousness

A scatterplot with regression line and R2 value showing the positive association between the left posterior insula and conscientiousness

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Figure 4: Summary of Gratitude-Modulated Brain Activity in Regions Modulated by Openness

A scatterplot with regression line and R2 value in each of the areas that was modulated by gratitude and associated (all negatively) with openness.

Figure 5: Summary of Gratitude-Modulated Brain Activity in Regions Modulated by Neuroticism

A scatterplot with regression line and R2 value in each of the areas that was modulated by gratitude and associated (all positively) with neuroticism.

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Table 1: Summary of Significant Results

The following regions of interest were associated either with i) activity during the ‘Reflection’ stage and a personality trait or ii) gratitude-modulated activity during the ‘Reflection’ stage and a personality trait.

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Discussion Our results indicate that agreeableness and conscientiousness are involved in modulating responses to gift-receipt in the brain, while neuroticism and conscientiousness are correlated to gratitude-modulated responses to gift-receipt in the brain. Agreeableness was negatively correlated with brain activity in the right anterior cingulate cortex (ACC), left temporal pole, and left medial prefrontal cortex (mPFC) during the gift-receipt reflection period. Both the ACC and mPFC are strongly linked to empathy: previous research indicates that the mPFC is recruited in tasks that require self-reflection and potentially participates in the default mode network, a network that is utilized when the brain attends to one’s own thoughts and feelings (Jenkins & Mitchell, 2011). The ACC has been shown to be active in pain and has shown higher activation when imagining oneself in pain as compared to others in pain (Jackson et al., 2006). The temporal lobe as a whole serves as a hub that integrates information associated with a concept (Bonner & Price, 2013). It has been proposed that more anterior regions (i.e. temporal pole) process fine-grained semantic information (Bonner & Price, 2013). Agreeableness has also been correlated to temporal lobe reactivity when negative associations are learned (Kennis et al., 2013). It thus appears that agreeableness, which is closely linked to empathy, modulates both the mPFC and the ACC, which have been previously linked with empathy, and the temporal lobe, which has been implicated in integrating sensory processing. Conscientiousness correlated positively with activity in the left posterior insula when participants reflected on the gifts they received. The insula has been implicated in emotional processing as well as interoception, the sense of the body’s physiological condition (Craig, 2002; Duerden et al., 2013). As conscientiousness is one of the traits most strongly associated with self-control and inhibition of impulses, an increase in insular activity likely reflects this increased self-awareness (Courbalay et al., 2015). Thus, in situations of gift-receipt, conscientiousness appears to modulate activity in the regions closely connected to empathy and self-perception. Openness was negatively correlated with gratitude-modulated activity in left secondary somatosensory cortex, right inferior posteromedial cortex, and right superior posteromedial cortex. While not much is known about the secondary somatosensory cortex’s role in emotional processing, it has been shown to play a role in sensory processing (Lockwood et al., 2013; Jackson et al., 2006). The anterior posteromedial cortex (PMC) has been implicated in self-processing as well as the default mode network in several studies (Cauda et al., 2010; Jackson et al., 2006; Kennis et al., 2013). In these regions, gratitude-correlated activity appears to be tapping into attentiveness to inner feelings, one of the six facets of openness. Gratitude is an emotion that inherently requires an understanding of internal feelings, and it appears that openness modulates this internal representation. Neuroticism correlated with an increase in gratitude-modulated activity in the left superior PMC, right superior PMC, and right anterior insula. As previously mentioned,

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the PMC appears to be related to the default mode network and has also been previously linked to neuroticism when ascribing negative stimuli to the self (Kennis et al., 2013). The insula has similarly been associated with neuroticism when subjects were exposed to negative or painful stimuli (Kennis et al., 2013). It is interesting that neuroticism, a trait characterized by an increased proneness to anxiety and stress, is able to explain variance in activity when gratitude is regressed with these regions, which are so closely tied to self-perception. It may be that the link between increased sensitivity to pain and high neuroticism is reduced by the propensity of gratitude (Wood, 2010). There appear to be two major networks that are modulated by personality that are involved in the experience of gratitude. The first is the default mode network, including the regions mPFC and the PMC. Activation of this network may indicate that gratitude is a reflective task, one that involves attention to one’s own feelings. The second network is that of sensory processing, as evidenced by activation in the ACC, insula, temporal pole, and secondary somatosensory cortex. As previous research has shown that gratitude can decrease the experience of pain, the negative activity in each of these areas may be the fMRI demonstration of that effect (Wood, 2010). Further studies should explore this circuitry as it may lead to a deeper understanding of the ways in which personality interacts with gratitude. Limitations: As with any study, ours contains several limitations that should be taken into account when interpreting results. Because this is an exploratory study, we have a fairly small sample size at only 22 participants. While this is often the case for fMRI studies, the associations shown here should guide further research in this area rather than being taken as undeniable fact. Furthermore, there were a few regions also implicated in emotional processing (e.g. the tempo-parietal junction) that we could have examined but were unable to due to time constraints. This would be an excellent area for future studies to explore. Finally, it is difficult to study gratitude because it can be subjective—if one person says they feel more grateful for a gift, it may reflect their perception of the ranking scale rather than their perception of gratitude. We combat this by utilizing a small scale and giving parameters to guide ratings; however, as with other studies of emotion, this is an issue that is difficult to control until technology advances to such a point that we no longer need self-reporting. Conclusion: Our findings confirm that different responses to gift-receipt are at least partially due to differences in personality. Agreeableness and openness appear to directly modulate brain activity when receiving gifts, while conscientiousness and neuroticism are correlated with gratitude-modulated brain activity. Regions of activation include areas implicated in i) emotional processing and ii) the default mode network, which indicates that gift-receipt appears to be a task involving self-awareness and understanding of emotion. The varying levels of activation as modulated by personality reflect the underlying neural mechanisms responsible for why different people can respond to the same gift differently.

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