Contents lists available at ScienceDirect Behavioural Brain Research journal homepage: www.elsevier.com/locate/bbr Research report Sex differences in rat decision-making: The confounding role of extraneous feeder sampling between trials Clifford H. Donovan, Scott A. Wong, Sienna H. Randolph, Rachel A. Stark, Robbin L. Gibb, Aaron J. Gruber ⁎ Canadian Centre for Behavioural Neuroscience, Department of Neuroscience, University of Lethbridge, 4401 University Drive West, Lethbridge, AB, T1K 6T5, Canada ARTICLE INFO Keywords: Rat Decision Sex Difference Exploration Lose-shift ABSTRACT Although male and female rats appear to perform differently in some tasks, a clear picture of sex differences in decision-making has yet to develop. This is in part due to significant variability arising from differences in strains and tasks. The aim of this study was to characterize the effects of sex on specific response elements in a re- inforcement learning task so as to help identify potential explanations for this variability. We found that the primary difference between sexes was the propensity to approach feeders out of the task context. This extraneous feeder sampling affects choice on subsequent trials in both sexes by promoting a lose-shift response away from the last feeder sampled. Female rats, however, were more likely to engage in this extraneous feeder sampling, and therefore exhibited a greater rate of this effect. Once trials following extraneous sampling were removed, there were no significant sex differences in any of the tested measures. These data suggest that feeder approach outside of the task context, which is often not recorded, could produce a confound in sex-based differences of reinforcement sensitivity in some tasks. 1. Introduction Men and women sometimes differ in the way they use past rewards to guide future choices. It has been suggested that men are more likely to exhibit risk-taking behaviour than women [1–3], whereas women have been suggested to be more sensitive to loss than men [3,4]. Much of the supporting evidence for these sex differences comes from tasks in which subjects choose among options with different expected values, the most prominent of which is the Iowa Gambling Task (IGT). There is strong evidence that men develop an undeviating preference for the optimal choice in fewer trials than do women (for review see: [4]). This difference in strategy has been interpreted as women exhibiting heightened loss-sensitivity relative to men. This interpretation is sup- ported by a recent meta-analysis of several other decision-making tasks [3]. Rodent studies of decision-making have revealed similar disparities due to sex in some situations [5,6], but the evidence is far less con- clusive (for review see: [7]). In a rodent analogue of the IGT, male Wistar rats collected more reward than females [8]. However, the same investigators found no sex differences when testing Long Evans rats on the same task [9]. Using a different adaptation of the IGT for rodents [10], another research group found no sex-based differences in Sprague-Dawley rats [11]. Other tasks have been utilized to investigate additional facets of rat decision-making, such as the risky decision- making task (RDT). In the RDT, rats choose between a safe lever, in which they consistently receive a small food reward, and a risky lever, in which they receive a larger food reward accompanied by an in- creasingly higher chance of receiving a foot shock. Male Long Evans rats chose the risky lever significantly more than the females [5]. Si- milar to results from human subjects, this effect may be interpreted as a measure of heightened loss-sensitivity in females or heightened risk- taking behaviour in males. Male Sprague-Dawley rats also displayed more impulsive responding than their female counterparts on a signal discrimination task [6]. However, contrary results have been found using delayed discounting tasks, which, are a direct measure of im- pulsive choice. In this paradigm, animals choose between a small, im- mediate reward and a larger, delayed reward. There has been no sex differences suggested from studies utilizing delayed discounting tasks in several strains of adult, drug naïve rats, including Long Evans rats [12], Sprague Dawley rats [13], or Wistar rats [14]. The inconsistency in the rat literature raises questions about the generalization of sex discrepancies in the choice domain across mam- malian brains. It is possible that this inconsistency is the product of some unexplained factor that is confounding the results. The control of https://doi.org/10.1016/j.bbr.2018.01.018 Received 16 November 2017; Received in revised form 8 January 2018; Accepted 16 January 2018 ⁎ Corresponding author at: University of Lethbridge, Department of Neuroscience, Canadian Centre for Behavioural Neuroscience, Polaris Brain Dynamics Research Group, 4401 University Drive West, Lethbridge, AB, T1K 6T5, Canada. E-mail address: aaron.gruber@uleth.ca (A.J. Gruber). Behavioural Brain Research 342 (2018) 62–69 0166-4328/ © 2018 Elsevier B.V. All rights reserved. T