Results:

Aknowledgements:We thank to all the participants that participated in this study.References:

King-Casas, B., & Chiu, P. H. (2012). Understanding interpersonal function in psychiatric illness through multiplayer economic games. Biological psychiatry,72(2), 119-125.

Polezzi, D., Daum, I., Rubaltelli, E., Lotto, L., Civai, C., Sartori, G., & Rumiati, R. (2008). Mentalizing in economic decision-making. Behavioural brain research, 190(2), 218-223.

Osinsky, R., Mussel, P., Öhrlein, L., & Hewig, J. (2013). A neural signature of the creation of social evaluation. Social cognitive and affective neuroscience, nst051.

Gehring, W. J., & Willoughby, A. R. (2002). The medial frontal cortex and the rapid processing of monetary gains and losses. Science, 295(5563), 2279-2282.

Discussion:

Methods:

3) Task feedback

After the UG, we asked the participants torate in a likert scale how many happiness,anger, sadness, betrayal and devaluationhe/she felt when facing some specific offersin the UG.

NEURAL ACTIVATION ASSOCIATED TO SOCIAL INTERACTIONS IN MAJOR DEPRESSION:

A STUDY USING EVENT RELATED POTENTIALS DURING THE ULTIMATUM GAME

2) Task: Ultimatum GameIn the UG, the participant (the responder) receives offers from other players (the proposers) on how to split a sum of money. If the

participant accepts the offer, the participant and the player who made the offer accumulate the money. If the participant rejects theoffer, both accumulate nothing.

We used a cover story to intensify the social factor in the UG: we showed 20 pictures to the participant and told him/her theywere some of the people who made the offers. We told him that at the end of the study he/she and the proposers would receive anon-monetary reward according to the money that each one accumulated. We also told the participant that he/she could make offersas a proposer to future participants and that he/she could gain extra money with these offers.

At the end of the session, we told the participant that in reality the offers were made by the research team and not by the peopleof the pictures.We asked he/she if it provoked any annoyance to him/her. Nobody reported feeling annoyance about that.

56 Fair offers (40% - 50%)

56 Medium offers (27% -33%)

56 Unfair offers (8% 23%)

5 4 5 4

5 45 4

+

2-3 s 1,5 s 1,5 s RT

3 s -RT

Trigger

Introduction:Major depression is a prevalent mental disorder and one of the leading causes of DALYs (Disability Adjusted Life Years). Major depression is characterized by deteriorated, negativeand unsatisfying social interactions (King-Casas & Chiu, 2012). These difficulties contribute to the low quality of life of those people. In spite of their importance, the neural basis ofsocial interactions in major depression remain unclear.

Recently, the field of neuroeconomics, that combines psychology, neuroscience and economy, has provided a manner to study social interactions quantitatively. One of the more usedtasks in neuroeconomics is the Ultimatum Game (UG). In this task the participant is presented with fair, medium and unfair monetary offers from others.

The Medial Frontal Negativity (MFN) is a negative component located in frontocentral sites with latency of 200-300 ms after stimulus presentation, and is more negative in lossesthan in gains on a gambling task (Gehring & Willoughby, 2002). The MFN has been related to error prediction processes and also to motivational or affective processes associated toearly outcome evaluation.

Some studies have investigated Event Related Potentials (ERPs) in healthy people during the UG. These studies reported that the MFN is more negative in unfair and medium offers than in fair offers (Osinsky et al., 2014; Polezzi et al., 2008). To our knowledge, there are no studies using ERPs during the UG in major depression.

We present results of an ongoing study analysing ERPs during the UG in people with major depression.

Objective:•This study aims to investigate neural bases associated to social interactions in major depression.• Specifically, this study aims to investigate the Medial Frontal Negativity during the Ultimatum Game in major depression.

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3) Task Feedback:

Our results indicate that the MFN is sensitive to fairness in the UG. This finding is in line with previous studies that relate the MFN to affective evaluation of outcomes.We still have not found a group effect or a group*type of offer interaction, may due to the sample limitations.We hope to contribute to the understanding of neural bases of social interactions in major depression.

4) Event Related Potentials:

Site of FCz electrode

Nicolaisen-Sobesky, E.1; Paz, V.1; Fernández-Theoduloz, G.1; Nievas, O.1; Garat, S.1; Pérez, A.1; Kessel, D.1; Cabana, Á.1; Gradin, VB1.1. Centro de Investigación Básica en Psicología, Facultad de Psicología, Universidad de la República, Montevideo, Uruguay.

1) Questionnaires

-Beck Depression Inventory (BDI)

-Liebowitz Social Anxiety Scale (LSAS)

-Anticipatory and ConsummatoryInterpersonal Pleasure Scale (ACIPS)

-Social Avoidance and Distress Scale (SAD)

-Fear of negative evaluation (FNE)

-State-Trait Anxiety Inventory (STAI)

-Rosenberg Self-Esteem Scale (RSES)

-Iowa-Netherlands Comparison OrientationScale (INCOM)

-Inventory of Interpersonal Problems (IIP)

-Snaith-Hamilton Pleasure Scale (SHAPS)

-Positive Affect Negative Affect Scale (PANAS)

4) EEG recording

The continuous EEG signal was recordedusing an elastic cap and the ActiveTwoBiosemi system with 64 active electrodes.

1) Questionnaires:

2) Task Behavior:

Control Depression

n 23 17

Age 22,17 ±3,55 22,59 ±3,954

BDI 0,95 ±1,117 26,92 ±7,088

We analysed the MFN in the 250-350 ms time window after offer presentation in the FCz electrode.

The MFN is more negative in unfair and medium offers tan in fair offers (p=0,032).

Participants reported feeling more happiness in fair offers than in medium andunfair offers and more happiness in medium offers than in unfair offers (p=0,000).

Participants reported feeling more anger, sadness, betrayal and devalue in unfairoffers than in medium and fair offers, and more of those emotions in mediumoffers than in fair offers (p=0,032).

Participants rejected moreunfair offers than mediumand fair offers, and moremedium than fair offers.(p=0,000).

Fair offersMedium offersUnfair offers

Depression-Fair offersDepression-Medium offersDepression-Unfair offers

Controls-Fair offersControls-Medium offersControls-Unfair offers

The depression group reported more interpersonal problems, anhedonia, negative affects, fear of negativeevaluation, orientation to social comparisons, and more symptoms of trait anxiety, state anxiety, and social anxiety. They also reported less interpersonal pleasure, positive affects and self-esteem. (p=0,000)

p=0,000 p=0,001 p=0,000 p=0,000 p=0,000

p=0,000 p=0,006 p=0,000 p=0,003 p=0,000

p=0,000

p=0,000

p=0,000

p=0,000 p=0,005 p=0,000 p=0,006p=0,000 p=0,011

Error bars denote standard deviations.