Licking microstructure and hedonic changes after flavour preference learning in rats

Pairing a neutral flavour conditioned stimulus (CS) with a nutrient reward will create a learned preference for that CS. Prior studies suggest that this is accompanied by an increase in the hedonic value of the CS, although the reliability of this effect is yet to be fully established. Here, flavour CS+s were mixed with either 16% sucrose or maltodextrin (with control CS-s mixed with 2% solutions of the same carbohydrate). While a reliable preference for the CS+ was seen in every case, and there was a learned increase in lick cluster size when all conditions were considered together, this difference was significant in only one experimental condition considered alone. A meta-analysis of these results and similar published licking microstructure analysis studies found that the Cohen’s dav effect size for changes in licking microstructure after flavour preference learning was 0.16. This is far smaller than the effect sizes reported when assessing learned hedonic changes in flavour preference based on other test or training methods. Although this confirms that flavour preference learning produces hedonic changes in the cue flavours, the analysis of licking microstructure with training based on voluntary consumption of CS and unconditioned stimulus (US) compounds may be an insensitive means of assessing such effects.

Implicit location probability learning does not induce baseline shifts of visuospatial attention

We tested whether implicit learning causes shifts of spatial attention in advance of or in response to stimulus onset. Participants completed randomly interspersed trials of letter search, which involved reporting the orientation of a T among Ls, and scene search, which involved identifying which of four scenes was from a target category (e.g., forest). In Experiment 1, an initial phase more often contained target letters in one screen quadrant, while the target scenes appeared equally often in all quadrants. Participants persistently prioritized letter targets in the more probable region, but the implicitly learned preference did not affect the unbiased scene task. In Experiment 2, the spatial probabilities of the scene and letter tasks reversed. Participants unaware of the probability manipulation acquired only a spatial bias to scene targets in the more probable region, with no effect on letter search. Instead of recruiting baseline shifts of spatial attention prior to stimulus onset, implicit learning of target probability yields task-dependent shifts of spatial attention following stimulus onset. Such shifts may involve attentional behaviors unique to certain task contexts.

Costly learning: preference for familiar food persists despite negative impact on survival

Animals often rely on events in their environment that provide information (i.e. experience) to alter their future decision-making in ways that are presumed to be beneficial. Such experience-based learning, however, does not always lead to adaptive decision-making. In this study, we use the omnivorous harvestman Heteromitobates discolor to explore the role of past diet on subsequent food choice and survival. We first tested whether a short-term homogeneous diet (rotten crickets, fresh crickets or dog food) influenced subsequent food choice (rotten cricket versus fresh cricket). We next examine the impact of diet on survival. We found that following experience with a homogeneous cricket diet, adult harvestmen displayed a learned preference for familiar food, regardless of whether it was rotten or fresh crickets; individuals experiencing dog food were equally likely to choose rotten versus fresh crickets. We additionally found that individuals that ate rotten crickets suffered shorter survival than those that ate fresh crickets. Together, our results suggest that the diet an individual experiences can lead to maladaptive food preferences—preferences that ultimately result in reduced longevity.

Enduring good memories of infant trauma: Rescue of adult neurobehavioral deficits via amygdala serotonin and corticosterone interaction

Children form a strong attachment to their caregiver—even when that caretaker is abusive. Paradoxically, despite the trauma experienced within this relationship, the child develops a preference for trauma-linked cues—a phenomenon known as trauma bonding. Although infant trauma compromises neurobehavioral development, the mechanisms underlying the interaction between infant trauma bonding (i.e., learned preference for trauma cues) and the long-term effects of trauma (i.e., depressive-like behavior, amygdala dysfunction) are unknown. We modeled infant trauma bonding by using odor-shock conditioning in rat pups, which engages the attachment system and produces a life-long preference for the odor that was paired with shock. In adulthood, this trauma-linked odor rescues depressive-like behavior and amygdala dysfunction, reduces corticosterone (CORT) levels, and exerts repair-related changes at the molecular level. Amygdala microarray after rescue implicates serotonin (5-HT) and glucocorticoids (GCs), and a causal role was verified through microinfusions. Blocking amygdala 5-HT eliminates the rescue effect; increasing amygdala 5-HT and blocking systemic CORT mimics it. Our findings suggest that infant trauma cues share properties with antidepressants and safety signals and provide insight into mechanisms by which infant trauma memories remain powerful throughout life.

Hand-preference training in the mouse reveals key elements of its learning and memory process and resolves the phenotypic complexity in the behaviour

Handedness in the mouse comprises 2 different behaviours. Some strains have a conditional behaviour, in that the mice learn a direction of hand preference in response to reaching for food, whereas other strains have an innate or constitutive behaviour, and prior experience has no measurable effect on their hand preference. However, hybrids from different strains have revealed both recessive and dominant forms of constitutive hand preference. We proposed that kinetic parameters of the learning process would resolve this genetic heterogeneity as well as the phenotypic complexity in the behaviour. We conducted and report here a detailed kinetic analysis of hand-preference training in the C57BL/6J strain. It revealed elements of the fundamental process of learning and long-term memory that underlies the behaviour by documenting consolidation of memory, blocking of this consolidation by an inhibitor of protein synthesis, retention of memory, and speed of learning in response to training reaches. Furthermore, speed of learning is clearly described by 2 parameters that we call "capacity" (or maximum amount of learned preference) and "ability" (or number of training reaches to achieve half the capacity). These 2 kinetic parameters can vary independently among genetically different strains that learn a preference, and we used them to demonstrate that the respective recessive and dominant forms of constitutive hand-preference may be the consequence of a true null or loss of function and a gain of function, possibly a memory regulator, in the learning process. The quantitative measures provide a sensitive and selective method to establish the fundamental learning process underlying mouse hand preference and to demonstrate empirically how genes and contextual environment shape its phenotypic complexity.Key words: mouse, hand-preference, behavioural genetics, learning, memory, complexity, kinetics, capacity, ability, memory regulator gene.

Associative learning of visual and gustatory cues in the large cabbage white butterfly, Pieris brassicae

The landing response of the large cabbage white butterfly Pieris brassicae was studied under controlled optical and gustatory stimulus conditions. Experience-based changes in landing behaviour were examined by offering cardboard circles of two different shades of green, treated with either an oviposition stimulant or a deterrent. We employed two training situations. In one situation the two shades of green, carrying either the stimulant or the deterrent, were offered simultaneously, in the other sequentially. During the 1 hour training periods, butterflies were either landing and drumming spontaneously or they were caught at the end of the period and placed on the artificial leaves until tarsal drumming ensued. Our experiments demonstrated that P. brassicae females can learn to associate visually detected substrate characteristics with contact-chemosensory information available only after landing. Furthermore, a learned preference for a substrate could be turned into a preference for the alternative substrate by exposing the insect to a deterrent on the previously preferred substrate. These results provide indications of aversion learning, thus far undocumented in oviposition behaviour of Lepidoptera. Bringing the butterflies into forced contact with the oviposition stimulant resulted in similar effects on landing preference compared to those of spontaneous landing, but spontaneous landing had a stronger effect on preference for associations involving the deterrent. The simultaneous training regime, which supposedly requires a less important role for short-term memory, was more effective in modifying landing preferences.

Sexual imprinting on a novel blue ornament in zebra finches

Sexual imprinting plays an important role for the development of mate preferences in birds. We tested whether male and female zebra finches Taeniopygia guttata sexually imprinted on an evolutionary novel trait, a blue feather on the forehead in parents. Additionally, we tested whether males and females would transfer a learned preference for the blue feather to a preference for blue leg bands, and whether a potential mate with two novel blue traits can amplify its attractiveness. Offspring were raised by parents in four different imprinting groups: (1) both parents unadorned; (2) the mother adorned only; (3) the father adorned only; (4) both parents adorned with the blue feather. After young reached maturity, we tested their mate preference for adorned and unadorned conspecifics of the opposite sex in binary choice tests. Females of the father adorned imprinting group sexually imprinted on the blue feather, and females reared by adorned parents showed a tendency to prefer adorned males. None of the males sexually imprinted on the blue feather. Our study replicates the results of a previous study on sexual imprinting on a red feather in zebra finches. We, therefore, propose a sex difference in the learning process of sexual imprinting. Females sexually imprinted on the blue feather did not transfer the learned preference to males with blue leg bands, and two novel blue traits could not amplify the attractiveness in males and females for the opposite sex. Our study emphasizes the role of sexual imprinting for the cultural evolution in mate preferences in zebra finches.