Serum omega-3 fatty acids are associated with ultimatum bargaining behavior Enzo Emanuele a, ⁎, Natascia Brondino b , Simona Re a , Marco Bertona a , Diego Geroldi a a Interdepartmental Center for Research in Molecular Medicine (CIRMC), University of Pavia, Viale Taramelli 24, I-27100 Pavia, Italy b Department of Applied Health and Behavioral Sciences, Section of Psychiatry, University of Pavia, Pavia, Italy abstract article info Article history: Received 1 June 2008 Received in revised form 25 August 2008 Accepted 26 September 2008 Keywords: Neuroeconomics Bargaining Ultimatum game Omega-3 fatty acids In the ultimatum game (UG), two players are involved to bargain over a division of a given sum of money. The proposer makes an ultimatum offer of a fraction of money, while the responder can either accept or reject the proposer's decision. In case of rejection of the proposed splitting by the responder, neither player gets anything. Adverse psychological reactions are deemed to play a role in the rejection of unfair offers. Low serum levels of omega-3 polyunsaturated fatty acids have been linked to impulse control and hostility. This study examined the serum omega-3 and omega-6 fractions in relation to the ultimatum bargaining behavior. Participants were sixty economy students (31 males and 29 females, mean age: 24.4± 2.3 years) who played a €10 ultimatum game. Ultimatum offers were constrained to be €5 (proposer keeps €5) or €1 (proposer keeps €9) to generate a roughly even split between fair (5:5) and unfair (1:9) offers. Fasting serum alpha-linolenic (ALA), eicosapentaenoic (EPA), docosahexaenoic acid (DHA), linoleic acid (LA) and arachidonic acid (AA) were assayed with gas chromatography. In participants who rejected unfair offers there was a significant depletion of ALA, EPA and DHA. Moreover, the ratio of serum omega-3/omega-6 fatty acids was significantly lower in patients who rejected unfair offers as compared to those who did not. The results of this study suggest that a depletion of the serum omega-3 fatty acids is associated with rejections of unfair ultimatum offers in an experimental neuroeconomic setting. © 2008 Elsevier Inc. All rights reserved. 1. Introduction One of the most widely used task for analyzing economic decision- making is the ultimatum game (UG) [1–3]. In the UG, two players are involved to bargain over a division of a given sum of money. The first player, named the proposer, makes an ultimatum offer of a fraction of money, while the second one, named the responder, can either accept or reject the proposer's decision. In case of rejection of the proposed splitting by the responder, neither player gets anything. There is consistent evidence that unfair offers in the UG are often rejected [4,5]. Rejections of free money in the UG conflict with the predictions of the standard economic model that people are self- interested rational maximizers. Although there is no broadly accepted cause for this phenomenon, situations in which rationality fails to predict actual behavior often involve a strong emotional component [6,7]. In ultimatum experiments, unfair offers often inspire anger, hostility and a desire for revenge [8,9]. Additionally, impulsiveness may affect decision making, and impulsive behavior could be involved in the rejection of remunerative, but unfair, offers [10]. There is evidence to suggest that lipid abnormalities may play a role in the neurobiology of human impulsiveness and aggressive behavior [11]. Interestingly, alterations in omega-3 plasma polyunsaturated fatty acids (PUFAs) have been implicated in impulsive and aggressive behaviors [12]. Accordingly, low serum omega-3 PUFAs have been found significant predictors of aggression in patients with psychiatric disorders [13] and frequency of externalizing behavior problems in boys [14]. Moreover, there is evidence to suggest that omega-3 fatty acid status is associated with variability in affect regulation, person- ality and impulse control in healthy adults [15]. It is not known whether the associations between serum omega-3 fatty acids status, anger and impulsivity observed in clinical samples and in the general population extend to experimental neuroeconomic behavior. Accord- ingly, the aim of the present investigation was to determine if serum omega-3 and omega-6 fatty acid could be associated with the irrational rejection of unfair UG offers in normal healthy individuals. We specifically focused on the analysis of three omega-3 fatty acids — namely alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) — and two omega-6 fatty acids — linoleic acid (LA) and arachidonic acid (AA). The ratio of omega-3/omega-6 was also examined. 2. Materials and methods 2.1. Study subjects The study sample has been previously described in detail [16]. A total of sixty undergraduate economy students (31 males and 29 females, mean age 24.4 ± 2.3 years; age range 22–28 years) were investigated. All participants were healthy nonsmoking subjects. Excluded were subjects Physiology & Behavior 96 (2009) 180–183 ⁎ Corresponding author. Tel./fax: +39 0382 528 341. E-mail address: enzo.em@libero.it (E. Emanuele). 0031-9384/$ – see front matter © 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.physbeh.2008.09.020 Contents lists available at ScienceDirect Physiology & Behavior journal homepage: www.elsevier.com/locate/phb