title: Delay discounting task in pigs reveals response strategies related to dopamine metabolite.
abstract: We developed a novel delay discounting task to investigate outcome impulsivity in pigs. As impulsivity can affect aggression, and might also relate to proactive and reactive coping styles, eight proactive (HR) and eight reactive (LR) pigs identified in a manual restraint test ("Backtest", after Bolhuis et al., 2003) were weaned and mixed in four pens of four unfamiliar pigs, so that each pen had two HR and two LR pigs, and aggression was scored in the 9h after mixing. In the delay discounting task, each pig chose between two levers, one always delivering a small immediate reward, the other a large delayed reward with daily increasing delays, impulsive individuals being the ones discounting the value of the large reward quicker. Two novel strategies emerged: some pigs gradually switched their preference towards the small reward ('Switchers') as predicted, but others persistently preferred the large reward until they stopped making choices ('Omitters'). Outcome impulsivity itself was unrelated to these strategies, to urinary serotonin metabolite (5-HIAA) or dopamine metabolite (HVA) levels, aggression at weaning, or coping style. However, HVA was relatively higher in Omitters than Switchers, and positively correlated with behavioural measures of indecisiveness and frustration during choosing. The delay discounting task thus revealed two response strategies that seemed to be related to the activity of the dopamine system and might indicate a difference in execution, rather than outcome, impulsivity.
authors: Centre for Behavioural Biology, Department of Clinical Veterinary Science, University of Bristol, Langford BS40 5DU, UK. Electronic address: luca.melotti@vetsuisse.unibe.ch.
authors: Luca
authors: L
authors: Melotti
authors: Liat Romme
authors: LR
authors: Thomsen
authors: Michael J
authors: MJ
authors: Toscano
authors: Michael
authors: M
authors: Mendl
authors: Suzanne
authors: S
authors: Held
mesh_terms: D000223:Adaptation, Psychological / Q000502:physiology; D000374:Aggression / Q000502:physiology; D000818:Animals; D002755:Choice Behavior; D003627:Data Interpretation, Statistical; D004298:Dopamine / Q000378:metabolism* / Q000652:urine; D005502:Food; D006128:Growth / Q000502:physiology; D006719:Homovanillic Acid / Q000378:metabolism; D006897:Hydroxyindoleacetic Acid / Q000378:metabolism; D007175:Impulsive Behavior / Q000378:metabolism* / Q000523:psychology*; D012149:Restraint, Physical; D012201:Reward; D012701:Serotonin / Q000652:urine; D013315:Stress, Psychological; D013552:Swine
chemical_list: D012701:Serotonin; D006897:Hydroxyindoleacetic Acid; D004298:Dopamine; D006719:Homovanillic Acid
keywords: Aggression; Coping style; Delay discounting; Dopamine; Impulsivity