Fins of Fury or Fainéant: Fluoxetine impacts the aggressive behavior of fighting fish (Betta splendens).

While an extensive literature has demonstrated that the selective serotonin reuptake inhibitor (SSRI) antidepressant fluoxetine, disrupts aggressive behavior in male Betta splendens the behavioral mechanisms underlying this disruption remain unknown. To elucidate the behavioral mechanism underlying fluoxetine, male fish were acutely exposed to a 10 µmol (0.0034578 µg/L) concentration of fluoxetine for 25 days using an ABA design. Male Betta splendens are naturally aggressive fish with well-studied and patterned behavioral responses. Importantly, aggressive behavior in this species can be conditionally primed allowing for examination of motivational components of behavior in addition to motor performance. The present study focused on using female fish as an ecologically relevant prime for eliciting aggressive behavior as a means of examining the motivational and motoric effects of fluoxetine. We found that male courtship with a female was strongly correlated with aggressive responding against a mirror. However, despite the strong correlation male fish were not found to have different levels of aggression or changes in aggressive responding when compared to males not primed with a female. Also, latency was not different between the no female prime and female prime males for either the excitatory mirror condition or inhibitory white wall condition, of which the fish had no preference. However, fluoxetine was found to have profound effects on all males in the study regardless of prime type, with increases in latency for the mirror and white wall and decreases in aggressive responding to the mirror. These results support the hypothesis that fluoxetine impairs aggressive motivation and movement in Betta splendens.

Sex differences in risk sensitivity under positive and negative budgets and predictors of choice.

The authors investigated sex differences in human risk sensitivity by using a computerized choice task with an energy budget analogue. In addition, they explored possible personality predictors of variance sensitivity. The authors modified the traditional energy budget model from those used in risk-sensitive foraging research with nonhuman animals for appropriate use with a human population. Participants chose between 2 computer icons, 1 yielding a fixed-point reward and the other offering variable points. Men were risk prone in the negative budget and risk averse in the positive budget. Women were risk averse in the negative budget. Personality was not predictive of risk-sensitive bias. Interpreting the results using an evolutionary model, the authors found support for a biological and environmental construct of risk-sensitive behavior.

Self-control in rhesus macaques (Macaca mulatta): controlling for differential stimulus exposure.

Previous research on self-control using macaques (Macaca fascicularis) showed these animals have a strong bias for a delayed, larger reinforcer (Self-control) over an immediate, smaller reinforcer (Impulsive). Typical studies of self-control have used a discrete trials methodology with a secondary discriminative stimulus during the delay periods. This results in a greater exposure to the stimulus representing the self-controlled option and may account for some of the early exclusive preference for self-control observed. The present experiment examined self-control bias in three rhesus macaques (Macaca mulatta) while controlling for differential durations of stimulus exposure. Subjects were presented stimuli via a computer monitor and made choices by touching the stimulus at which point both stimuli were removed for the delay periods. All three subjects displayed a nearly exclusive bias for the delayed, larger reinforcer self-control). These results are consistent with previous studies, despite the variations in methodology and species.

Increased effort requirements and risk sensitivity: a comparison of delay and magnitude manipulations.

Reward magnitude and delay to reward were independently manipulated in two separate experiments examining risk-sensitive choice in rats. A dual-running wheel apparatus was used and the tangential force resistance required to displace both wheels was low (50g) for half of the subjects, and high (120g) for the remaining subjects. Concurrent FI30-s and FI60-s schedules delivered equivalent amounts of food reward per unit time (i.e. 5 and 10 pellets of food, respectively), and these conditions served as the baseline treatment for all subjects. Variability, either in reward magnitude or delay, was introduced on the long-delay (60s) schedule during the second phase. All subjects were returned to the baseline condition in the third phase, and variability was introduced on the short-delay (30s) interval schedule during phase four. The subjects were again returned to the baseline condition in the fifth and final phase, ultimately yielding a five-phase ABACA design. Original baseline performance was characterized by a slight short-delay interval preference, and this pattern of performance was recovered with each subsequent presentation of the baseline condition. Overall, the data obtained from the reward magnitude and delay-to-reward manipulations were indistinguishable; subjects experiencing low-response effort requirement behaved in a risk-indifferent manner and subjects experiencing high-response effort requirement preferred the variable schedule. Implications for the daily energy budget rule on risk-sensitive foraging are discussed in light of these findings.