Intrinsic exploration in animals: motives and measurement

Olfactory investigation in the home cage

We have developed a behavioral paradigm to study volitional olfactory investigation in mice over several months. We placed odor ports in the wall of a standard cage that administer a neutral odorant stimulus when a mouse pokes its nose inside. Even though animals were fed and watered ad libitum, and sampling from the port elicited no outcome other than the delivery of an odor, mice readily sampled these stimuli hundreds of times per day. This self-paced olfactory investigation persisted for weeks with only modest habituation following the first day of exposure to a given set of odorants. If an unexpected odorant stimulus was administered at the port, the sampling rate increased transiently (in the first 20 min) by an order of magnitude and remained higher than baseline throughout the subsequent day, indicating learned implicit knowledge. Thus, this system may be used to study naturalistic olfactory learning over extended time scales outside of conventional task structures.

Effect of light intensity, spectrum, and uniformity on the ability of dairy cows to navigate through an obstacle course

The most suitable light intensity for cows during nighttime has not been thoroughly investigated. Recommendations on the night-time lighting regimen on dairy farms differ between countries and range from light throughout the night to darkness to allow the animals a rest from artificial light. Commercial actors recommend red light for night-time lighting in cattle barns to facilitate livestock supervision with minimum disturbance for the animals. However, little is known about how light intensity, spectrum, and uniformity affect the ability of cows to navigate their indoor environment. Thus, in a change-over study with 12 pregnant, nonlactating dairy cows, we observed how the cows walked through an obstacle course under different light treatments. Obstacles were positioned differently for every run, to present a novel challenge for each light environment. Fourteen different light treatments were tested, involving intensity ranging from <0.01 (darkness) to 4.49 µmol m-2 s-1, high or low uniformity, and white or red color. Light was characterized in terms of illuminance, photon flux density, spectral composition, and uniformity. Additionally, assessment of the environmental light field was used to describe each lighting condition from a bovine and human perspective. Data were analyzed in a generalized mixed model to assess whether lighting conditions affected cow walking speed or stride rate. Pair-wise post hoc comparisons showed that the cows walked at a slower speed in nonuniform red light compared with uniform white light or uniform red light. Interestingly, darkness did not alter walking speed or stride rate. The odds of different behaviors occurring were not affected by lighting conditions. In conclusion, darkness did not affect the ability of cows to navigate through the obstacle course, but medium-intensity, nonuniform red light affected their speed. Hence, cows do not necessarily need night-time lighting to navigate, even in a test arena with obstacles blocking their way, but nonuniform light distribution may have an effect on their movements.

Fish personality: meta-theoretical issues, personality dimensions, and applications to neuroscience and psychopathology

While the field of personality neuroscience has extensively focused on humans and, in a few cases, primates and rodents, a wide range of research on fish personality has emerged in the last decades. This research is focused mainly on the ecological and evolutionary causes of individual differences and also aimed less extensively at proximal mechanisms (e.g., neurochemistry or genetics). We argue that, if consistent and intentional work is made to solve some of the meta-theoretical issues of personality research both on fish and mammals, fish personality research can lead to important advances in personality neuroscience as a whole. The five dimensions of personality in fish (shyness-boldness, exploration-avoidance, activity, aggressiveness, and sociability) need to be translated into models that explicitly recognize the impacts of personality in psychopathology, synergizing research on fish as model organisms in experimental psychopathology, personality neuroscience, and ecological-ethological approaches to the evolutionary underpinnings of personality to produce a powerful framework to understand individual differences.

The combined role of visual and olfactory cues in foraging by Cataglyphis ants in laboratory mazes

Foragers use several senses to locate food, and many animals rely on vision and smell. It is beneficial not to rely on a single sense, which might fail under certain conditions. We examined the contribution of vision and smell to foraging and maze exploration under laboratory conditions using Cataglyphis desert ants as a model. Foraging intensity, measured as the number of workers entering the maze and arriving at the target as well as target arrival time, were greater when food, blue light, or both were offered or presented in contrast to a control. Workers trained to forage for a combined food and light cue elevated their foraging intensity with experience. However, foraging intensity was not higher when using both cues simultaneously than in either one of the two alone. Following training, we split between the two cues and moved either the food or the blue light to the opposite maze corner. This manipulation impaired foraging success by either leading to fewer workers arriving at the target cell (when the light stayed and the food was moved) or to more workers arriving at the opposite target cell, empty of food (when the food stayed and the light was moved). This result indicates that ant workers use both senses when foraging for food and readily associate light with food.

Association with Different Housing and Welfare Parameters on Results of a Novel Object Test in Laying Hen Flocks on Farm

The objective of this on-farm study was to determine if flocks showing feather damage and/or cannibalism would have a higher fear response to the novel object (NOT) and the association between different housing and welfare parameters on results of the NOT. Therefore, 16 flocks were observed during the laying period in Germany. In total, there were six barns, seven free-range, and three organic flocks. The plumage and integument condition of 50 birds of each flock were evaluated at 4 different times during the laying period (V1: 18th to 23rd week of life, V2: 26th to 35th week of life, V3: 49th to 57th week of life, V4: 61st to 73rd week of life). At the same observation times, the NOT was performed in the flocks (at four different locations per visit time). Based on the average number of hens gathered around the novel object (NO) within the period of two minutes, conclusions can be made about the fearfulness of the flock. The present study shows that the more fearful a flock was, the more frequent feather damage (p < 0.001) and cannibalism (p < 0.01) occurred. Age and flock size were associated with fearfulness. Fearfulness of hens increased with the increasing age of hens (p < 0.001) and with an increasing flock size (p < 0.001). Hens of white feather color appeared to be more fearful than brown hens (p < 0.001). Hens kept on barn farms showed significantly lower numbers of hens around the novel object (p < 0.001) than on free-range farms, which possibly indicates that having permanent access to outdoor space generally appears to be associated with the fearfulness of a flock.

Novelty during rearing increased inquisitive exploration but was not related to early ranging behavior of laying hens

Range use by free-range laying hen flocks is heterogeneous. We hypothesized that ranging behaviour may be motivated by curiosity and thwarted by fearfulness. This project aimed to increase a hen’s motivation to explore by enriching the rearing environment and identify relationships between exploration, fear and ranging. Day-old Hy-Line chicks (n = 1700) were reared in environments that provided novel items, structures for perching or an industry standard floor rearing environment. Prior to range access, fear and exploratory behaviors were assessed at 18 weeks of age (cohort 1; n = 30 hens/treatment) via novel arena and novel object tests and at 22 weeks of age (cohort 2; n = 30 hens/treatment) using an 8-arm radial maze choice paradigm adapted from previous rodent research. Hens were trained to expect success in two arms (reward) and failure in two arms (mild punishment), the remaining four arms (ambiguous arms) were not available during training. After training, all hens were retested for 8 minutes with access to the four familiar arms only, then for four minutes with access to the ambiguous arms for the first time, in addition to the success and failure arms. Latency to enter the ambiguous arms and the number of ambiguous arms entered were assessed as an indicator of a hen’s willingness to forgo reward and risk punishment to explore a novel area. At 25 weeks of age, hens were provided with range access and individual range access was monitored for three weeks. Latency to access the range and the number of days the range was accessed was not related to rearing treatment (p &gt; 0.05) and was only weakly correlated with behavior during the novel arena, novel object and 8-arm radial maze tests (r &lt; 0.3). However, hens reared in the novelty rearing environment were more willing to forgo reward to explore the ambiguous arms than hens reared in the control environment (p = 0.004). We did not identify strong evidence that exploration or fearfulness was related to early ranging behavior. However, we show that motivation to explore increases when hens are reared in an enriched environment.

The Case for Octopus Consciousness: Valence

Octopuses may demonstrate perceptual richness, neural unity, temporality, and finally, valence or affective evaluation, as the neural basis for consciousness. Octopuses attach a positive valence to food as ‘specializing generalists’ with long-term learning and flexible choices. They value shelter, yet modify, adapt and even transport it where necessary. They attach a negative valence to what may be described as pain, monitoring and protecting the damaged area and learning to associate locations with pain relief. Finally and surprisingly, octopuses attach a negative value to uncertainty so that they explore their environment before exploiting certain aspects of it and even exhibit motor play. This series of four papers, culminating in the present one, demonstrates in detail why the Cambridge Declaration of Consciousness has suggested octopuses might have the substrate for consciousness, although it is likely not similar to or as complex as that shown by ‘higher’ vertebrate lineages.

Striatal dopamine explains novelty-induced behavioral dynamics and individual variability in threat prediction

Animals both explore and avoid novel objects in the environment, but the neural mechanisms that underlie these behaviors and their dynamics remain uncharacterized. Here, we used multi-point tracking (DeepLabCut) and behavioral segmentation (MoSeq) to characterize the behavior of mice freely interacting with a novel object. Novelty elicits a characteristic sequence of behavior, starting with investigatory approach and culminating in object engagement or avoidance. Dopamine in the tail of the striatum (TS) suppresses engagement, and dopamine responses were predictive of individual variability in behavior. Behavioral dynamics and individual variability are explained by a reinforcement-learning (RL) model of threat prediction in which behavior arises from a novelty-induced initial threat prediction (akin to "shaping bonus") and a threat prediction that is learned through dopamine-mediated threat prediction errors. These results uncover an algorithmic similarity between reward- and threat-related dopamine sub-systems.

Activity vs exploration: Locomotion in a known and unknown environment differs in Atlantic cod juveniles (Gadus morhua)

Individuals within a population often behave differently and these differences can be consistent over time and/or context, also termed "animal personality". Animal personality has been commonly classified into five axes with studies aiming to validate these axes. One subject that has surprisingly not received full attention yet is the difference between the two personality axes "activity" and "exploration-avoidance", i.e. behaviour in a known vs an unknown environment. Despite this clear difference in definition, many studies measure activity in an unknown environment and term it activity, while underlying motivations between the two environments are different. This study aimed to detect the two personality traits "activity" and "exploration" in Atlantic cod juveniles, and to investigate whether they support the distinctive definitions proposed by previous authors. This study showed significant consistency in locomotion variation in both environments, i.e. personality. In addition, the two environments clearly elicited different behaviours; Atlantic cod juvenile behaviour was more repeatable and they moved more in the known vs the unknown environment, and no correlation of the proportional locomotion between the two was found. This demonstrates that locomotion in both environments, i.e. the personality axes "activity" and "exploration", should not be confused nor treated as if they reflect the same personality trait.

Housing Environment Affects Pubertal Onset, Anxiety-like Behavior, and Object Interaction in Male and Female Long Evans Rats

Rodents used for research can be humanely housed in a variety of ways. As such, a vast number of different housing environments are used, but are often not described in research publications. However, many elements of housing environments, including bedding, diet, water bottles, and cage material, can expose rodents to natural and synthetic compounds that can have lasting effects on the body, brain, and behavior. Some environmental items contain endocrine-disrupting compounds (EDCs), which can affect many commonly assessed physiological and behavioral endpoints in rodents. Here, we compare the effects of 2 commonly used housing environments for male and female Long Evans rats on body weight, pubertal onset, and a battery of behavioral tests measuring activity, anxiety-like behavior, and cognition. One standard environment was comparatively high in EDCs (standard rodent chow, plastic cages, plastic water bottles, and corncob bedding), while the other was a relatively low-EDC environment (phytoestrogen-free chow, polysulfone cages, glass water bottles, and wood-chip bedding). As compared with the Standard group, rats raised in the Low-EDC environment reached puberty earlier, displayed less anxiety-like behavior in the elevated plus maze and open field test, and showed less overall object exploration in the novel object recognition task. These effects occurred only if rats had been raised in these conditions since conception. An acute change from one environment to the other in adulthood did not yield these same effects. These results provide further evidence for the effects of common housing environments on development and behavior and highlight the importance of reporting environmental conditions in the literature to promote reproducibility in research using animal subjects.

Curiosity in zebrafish (Danio rerio)? Behavioral responses to 30 novel objects

Curiosity-the motivation to seek out information-has been studied widely across the animal kingdom. To investigate curiosity in zebrafish we presented 30 novel objects to groups of zebrafish housed in semi-naturalistic tanks (6 tanks; 10 fish/tank; 10-min presentations). During the first 100 s and final 100 s of each object's 10-min presentation period, we recorded each group's: (i) latency to approach the object, (ii) attraction to the object, (iii) social dynamics: agonistic behavior and group cohesion and coordination, and (iv) diving behavior, a stress response in zebrafish. Comparing these behaviors to a 100 s baseline period when no object was present, we tested for neophobia (avoidance of novelty), neophilia (overall attraction to novelty), sustained interest (prolonged attraction to at least some presentations), discriminant interest (certain objects eliciting more attention than others), habituation (loss of interest over time), and alterations to social and stress behaviors. Zebrafish groups readily approached all objects (1 s median latency), were neophilic throughout all object presentations, and showed systematic sustained interest only for some object presentations at the beginning of the study (object presentations 1-10). Over the course of the study, zebrafish also showed signs of habituation such that by the final ten object presentations (21-30), there were no signs of overall sustained interest. During the beginning of the study (object presentations 1-10), we also found evidence for specific object-driven interest, with object ID accounting for 11% of the variability in interest scores (p < 0.01), and object-driven interest corresponding to alterations in social behavior: decreased aggression (p < 0.02), increased group cohesion (p < 0.02), and increased group coordination (p < 0.05). By explicitly investigating curiosity in fish, this work reveals that under certain conditions, zebrafish voluntarily engage in cognitive stimulation opportunities. More work is needed to clarify what types of information zebrafish find most rewarding and how long-term exposure to such opportunities may affect fish welfare.

Reaction to novelty as a behavioral assay of recognition memory in homing pigeons and Japanese quail

Spontaneous novelty preference is apparent in a wide array of animals, including mammals, birds, reptiles, and fish. This provides a powerful behavioral assay to assess whether an animal can recognize a diverse array of stimuli in a common paradigm. Surprisingly, no research has been conducted in birds using novelty approach under conditions comparable to the spontaneous object recognition (SOR) protocols that have become standard across other animals. To correct this, the current study adapts a number of SOR protocols commonly used in mammals to characterize novelty approach in Silver King pigeons and Japanese quail. We show that, in general, both quail and pigeons readily approach novel objects or locations when tested using SOR protocols, although pigeons show a neophilic response under some conditions in which quail do not. Neither quail nor pigeons readily approach objects in novel contexts or novel locations. These data show that SOR can be successfully adapted to birds, allowing for more direct comparison between mammals and birds in tasks of shared ecological relevance.

An Inhibitory Medial Preoptic Circuit Mediates Innate Exploration

Animals have an innate motivation to explore objects and environments with unknown values. To this end, they need to activate neural pathways that enable exploration. Here, we reveal that photostimulation of a subset of medial preoptic area (MPA) neurons expressing the vesicular-GABA transporter gene (vgat+) and sending axonal projections to the ventrolateral periaqueductal gray (vPAG) increases exploration in a chamber but causes no place preference when tested there without photostimulation. Photoinhibition of MPA^vgat–vPAG projections leads to no emotional changes as measured by normal activity in an open field assay. Electrophysiological recordings revealed that most GABAergic vPAG neurons are inhibited by MPA^vgat neurons. In contrast to a previous report that suggested that MPA^vgat–vPAG neurons may impart positive valence to induce place preference, our results suggest that these neurons can increase innate exploration.

Mice in a labyrinth show rapid learning, sudden insight, and efficient exploration

Animals learn certain complex tasks remarkably fast, sometimes after a single experience. What behavioral algorithms support this efficiency? Many contemporary studies based on two-alternative-forced-choice (2AFC) tasks observe only slow or incomplete learning. As an alternative, we study the unconstrained behavior of mice in a complex labyrinth and measure the dynamics of learning and the behaviors that enable it. A mouse in the labyrinth makes ~2000 navigation decisions per hour. The animal explores the maze, quickly discovers the location of a reward, and executes correct 10-bit choices after only 10 reward experiences — a learning rate 1000-fold higher than in 2AFC experiments. Many mice improve discontinuously from one minute to the next, suggesting moments of sudden insight about the structure of the labyrinth. The underlying search algorithm does not require a global memory of places visited and is largely explained by purely local turning rules.

Cage-lid hanging behavior as a translationally relevant measure of pain in mice

ABSTRACT

The development of new analgesic drugs has been hampered by the inability to translate preclinical findings to humans. This failure is due in part to the weak connection between commonly used pain outcome measures in rodents and the clinical symptoms of chronic pain. Most rodent studies rely on the use of experimenter-evoked measures of pain and assess behavior under ethologically unnatural conditions, which limits the translational potential of preclinical research. Here, we addressed this problem by conducting an unbiased, prospective study of behavioral changes in mice within a natural homecage environment using conventional preclinical pain assays. Unexpectedly, we observed that cage-lid hanging, a species-specific elective behavior, was the only homecage behavior reliably impacted by pain assays. Noxious stimuli reduced hanging behavior in an intensity-dependent manner, and the reduction in hanging could be restored by analgesics. Finally, we developed an automated approach to assess hanging behavior. Collectively, our results indicate that the depression of hanging behavior is a novel, ethologically valid, and translationally relevant pain outcome measure in mice that could facilitate the study of pain and analgesic development.

Location and temporal memory of objects declines in aged marmosets (Callithrix jacchus)

Episodic memory decline is an early marker of cognitive aging in human. Although controversial in animals and called “episodic-like memory”, several models have been successfully developed, however they rarely focused on ageing. While marmoset is an emerging primate model in aging science, episodic-like memory has never been tested in this species and importantly in aged marmosets. Here, we examined if the recall of the what-when and what-where building blocks of episodic-like memory declines in ageing marmosets. We developed a naturalistic approach using spontaneous exploration of real objects by young and old marmosets in the home cage. We implemented a three-trial task with 1 week inter-trial interval. Two different sets of identical objects were presented in sample trials 1 and 2, respectively. For the test trial, two objects from each set were presented in a former position and two in a new one. We quantified the exploratory behaviour and calculated discrimination indices in a cohort of 20 marmosets. Young animals presented a preserved memory for combined what-where, and what-when components of the experiment, which declined with aging. These findings lead one to expect episodic-like memory deficits in aged marmosets.

Novelty-induced hyperactivity and suppressed cocaine induced locomotor activation in mice lacking threonine 53 phosphorylation of dopamine transporter

Dopamine (DA) transporter (DAT) is dynamically regulated by several protein kinases and the Thr53 phosphorylation of DAT (pT53-DAT) is documented in heterologous cell models and in rat brain. However, the role of endogenous pT53-DAT in living animals has never been addressed. Here we generated and studied the pT53-lacking DAT mouse model (DAT-Ala53) by CRISPR/Cas9 technology. DAT-Ala53 mice showed normal growth, body weight, body temperature, grip strength, and sucrose preference while pT53-DAT was completely absent. However, DAT-Ala53 mice showed hyperlocomotion, pronounced vertical exploratory behavior, and stereotypy in a novel environment compared to wild-type littermates (WT). DAT-Ala53 mice displayed unaltered levels of monoamines, glutamate, and GABA in the striatum compared to WT. There were also no significant differences between DAT-Ala53 mice and WT in tyrosine hydroxylase (TH) and phospho-TH levels, or in total and surface DAT levels, or in DA-transport kinetic parameters V_max and K_m. Immunohistochemical and colocalization analyses of TH and DAT in caudate-putamen and nucleus accumbens revealed no significant differences between DAT-Ala53 and WT mice. Interestingly, cocaine's potency to inhibit striatal DA transport and cocaine-induced locomotor activation were significantly reduced in the DAT-Ala53 mice. Also, ERK1/2 inhibitors completely failed to inhibit striatal DA uptake in DAT-Ala53 mice. Collectively, our findings reveal that the mice lacking pT53-DAT display novelty-induced hyperactive phenotype despite having normal transporter protein expression, DA-transport kinetics and DA-linked markers. The results also reveal that the lack of endogenous pT53-DAT renders DAT resistant to ERK1/2 inhibition and also less susceptible to cocaine inhibition and cocaine-evoked locomotor stimulation.

Welfare-Related Behaviors in Chickens: Characterization of Fear and Exploration in Local and Commercial Chicken Strains

Fear and exploration are crucial traits determining how animals behave in novel situations, and thus, they influence animal welfare. The aim of this study was the characterization of these behavioral traits among different strains to identify interesting alternatives for future poultry production. Whereas the Novel Object Test (NOT) focuses on fear and exploration of novel objects, the Avoidance Distance Test (ADT) addresses this in the context of humans. Here, a commercial hybrid line, a dual-purpose hybrid and a local adapted strain were tested. For the differences between strains and development of fear, Lohmann Brown (n = 714), Lohmann Dual (n = 844) and Rhinelander (n = 458) were observed weekly until maturity. Results show that fear and exploration towards unknown objects and humans are breed-specific (all p < 0.01). Additionally, development of fear in NOT and ADT differed between all three strains (both p < 0.01). The expressions of fear of humans or objects should be regarded as characteristics adapted for different husbandry systems and breeding goals, e.g., high exploratory behavior in aviary or high avoidance of predators in free-ranging husbandry or at least a balanced ratio between fear and exploration. Characterization of behavioral traits among different strains, understanding diversity and integrating these behaviors into future breeding and husbandry systems might reflect the need to preserve local strains and the potential to improve animal welfare.

When perceptual laterality vanishes with curiosity: A study in dolphins and starlings

Sensory laterality is influenced by the individual's attentional state. There are variations in the way different individuals of a same species attend to stimuli. When confronted to novelty, some individuals are more explorative than others. Curiosity is composed of sensation and knowledge seeking in humans. In the present study, we hypothesized that more curious animals, i.e., showing more sensory exploration would be less lateralized than quietly attentive individuals, performing instead more gazing behaviours. In order to test this hypothesis and its possible generality, we performed two studies using two animal models (dolphins and starlings) and two modalities (visual and auditory) of presentation of species-specific and non-species-specific stimuli. Both dolphins and starlings presented more gazes for the species-specific stimuli and more exploratory components for the non-species-specific stimuli. Moreover, in both cases, the non-species-specific stimuli involved more lateralized responses whereas there was no or less clear laterality for the species-specific stimuli. The more exploratory dolphins and starlings also showed a decreased laterality: the more "curious" individuals showed no laterality. Further studies are needed on characterization of curiosity in relation to attention structure. The present study suggests that individual variations in sensory laterality may help disentangle the subtle differences between curiosity, attention and boldness.

Relationship between exploratory activity and adrenocortical activity in the black rat (Rattus rattus)

The relationship between physiological and behavioral stress markers is documented in several rodent species. However, there is no information regarding the role of adrenocortical activity in behavior of the black rat (Rattus rattus). Therefore, we hypothesize that the adrenocortical activity of black rats varies between individuals and is related to some of the behaviors in a novel environment. To test this hypothesis, we (i) validated a method for quantifying glucocorticoid metabolites from feces (fGCMs) with an enzyme immunoassay (EIA); (ii) examined variation and diurnal rhythms of feces and GCM production; and (iii) examined the relationship between GCM levels and exploratory behavioral traits. We fulfilled the first aim (i) by successfully performing an ACTH challenge test to validate the use of a 5α-pregnane-3β,11β,21-triol-20-one EIA for measuring fGCMs. Second (ii) we detected considerable consistent interindividual variability in production of both feces and glucocorticoids. The peak production of feces occurred in the first hour of the dark cycle, the peak of fGCMs occurred approximately 3 h later. Lastly, (iii) there was no clear relationship between behavior in the hole board test and GCMs. Grooming, a typical behavioral stress marker, was negatively associated with stress reactivity, while head-dipping in the hole-board test (traditionally considered an exploratory behavior independent of stress) was not correlated with the GCMs. This study offers a first look at GCMs in the black rat, successfully validates a method for their measurement and opens possibilities for future research of the relationship between glucocorticoids and exploratory behavior in this species.

Epigenetics of Animal Personality: DNA Methylation Cannot Explain the Heritability of Exploratory Behavior in a Songbird

The search for the hereditary mechanisms underlying quantitative traits traditionally focused on the identification of underlying genomic polymorphisms such as single-nucleotide polymorphisms. It has now become clear that epigenetic mechanisms, such as DNA methylation, can consistently alter gene expression over multiple generations. It is unclear, however, if and how DNA methylation can stably be transferred from one generation to the next and can thereby be a component of the heritable variation of a trait. In this study, we explore whether DNA methylation responds to phenotypic selection using whole-genome and genome-wide bisulfite approaches. We assessed differential erythrocyte DNA methylation patterns between extreme personality types in the Great Tit (Parus major). For this, we used individuals from a four-generation artificial bi-directional selection experiment and siblings from eight F2 inter-cross families. We find no differentially methylated sites when comparing the selected personality lines, providing no evidence for the so-called epialleles associated with exploratory behavior. Using a pair-wise sibling design in the F2 intercrosses, we show that the genome-wide DNA methylation profiles of individuals are mainly explained by family structure, indicating that the majority of variation in DNA methylation in CpG sites between individuals can be explained by genetic differences. Although we found some candidates explaining behavioral differences between F2 siblings, we could not confirm this with a whole-genome approach, thereby confirming the absence of epialleles in these F2 intercrosses. We conclude that while epigenetic variation may underlie phenotypic variation in behavioral traits, we were not able to find evidence that DNA methylation can explain heritable variation in personality traits in Great Tits.

Cell type-specific genetic reconstitution of CB1 receptor subsets to assess their role in exploratory behaviour, sociability, and memory

Several studies support the notion that exploratory behaviour depends on the functionality of the cannabinoid type 1 (CB1) receptor in a cell type-specific manner. Mice lacking the CB1 receptor in forebrain GABAergic or dorsal telencephalic glutamatergic neurons have served as essential tools revealing the necessary CB1 receptor functions in these two neuronal populations. However, whether these specific CB1 receptor populations are also sufficient within the endocannabinoid system for wild-type-like exploratory behaviour has remained unknown. To evaluate cell-type-specific sufficiency of CB1 receptor signalling exclusively in dorsal telencephalic glutamatergic neurons (Glu-CB1-RS) or in forebrain GABAergic neurons (GABA-CB1-RS), we utilised a mouse model in which CB1 receptor expression can be reactivated conditionally at endogenous levels from a complete CB1-KO background. The two types of conditional CB1-rescue mice were compared with CB1 receptor-deficient [no reactivation (Stop-CB1)] and wild-type [ubiquitous reactivation of endogenous CB1 receptor (CB1-RS)] controls to investigate the behavioural consequences. We evaluated social and object exploratory behaviour in four different paradigms. Remarkably, the reduced exploration observed in Stop-CB1 animals was rescued in Glu-CB1-RS mice and sometimes even surpassed CB1-RS (wild-type) exploration. In contrast, GABA-CB1-RS animals showed the lowest exploratory drive in all paradigms, with an even stronger phenotype than Stop-CB1 mice. Interestingly, these effects weakened with increasing familiarity with the environment, suggesting a causal role for altered neophobia in the observed phenotypes. Taken together, using our genetic approach, we were able to substantiate the opposing role of the CB1 receptor in dorsal telencephalic glutamatergic versus forebrain GABAergic neurons regarding exploratory behaviour.

A new "sudden fright paradigm" to explore the role of (epi)genetic modulations of the DAT gene in fear-induced avoidance behavior

Alterations in dopamine (DA) reuptake are involved in several psychiatric disorders whose symptoms can be investigated in knock out rats for the DA transporter (DAT-KO). Recent studies evidenced the role of epigenetic DAT modulation in depressive-like behavior. Accordingly, we used heterozygous (HET) rats born from both HET parents (termed MIX-HET), compared to HET rats born from WT-mother and KO-father (MAT-HET), implementing the role of maternal care on DAT modulation. We developed a "sudden fright" paradigm (based on dark-light test) to study reaction to fearful inputs in the DAT-KO, MAT-HET, MIX-HET, and WT groups. Rats could freely explore the whole 3-chambers apparatus; then, they were gently confined in one room where they experienced the fright; finally, they could freely move again. As expected, after the fearful stimulus only MAT-HET rats showed a different behavior consisting of avoidance towards the fear-associated chamber, compared to WT rats. Furthermore, ex-vivo immuno-fluorescence reveals higher prefrontal DAT levels in MAT-HET compared to MIX-HET and WT rats. Immuno-fluorescence shows also a different histone deacetylase (HDAC) enzymes concentration. Since HDAC concentration could modulate gene expression, within MAT-HET fore brain, the enhanced expression of DAT could well impair the corticostriatal-thalamic circuit, thus causing aberrant avoidance behavior (observed only in MAT-HET rats). DAT expression seems to be linked to a simply different breeding condition, which points to a reduced care by HET dams for epigenetic regulation. This could imply significant prefronto-cortical influences onto the emotional processes: hence an excessively frightful response, even to mild stressful agents, may draw developmental trajectories toward anxious and depressed-like behavior.

Sham surgeries for central and peripheral neural injuries persistently enhance pain-avoidance behavior as revealed by an operant conflict test

Studies using rodent models of neuropathic pain use sham surgery control procedures that cause deep tissue damage. Sham surgeries would thus be expected to induce potentially long-lasting postsurgical pain, but little evidence for such pain has been reported. Operant tests of voluntary behavior can reveal negative motivational and cognitive aspects of pain that may provide sensitive tools for detecting pain-related alterations. In a previously described operant mechanical conflict test involving lengthy familiarization and training, rodents freely choose to either escape from a brightly lit chamber by crossing sharp probes or refuse to cross. Here, we describe a brief (2-day) mechanical conflict protocol that exploits rats' innate exploratory response to a novel environment to detect persistently enhanced pain-avoidance behavior after sham surgeries for 2 neural injury models: thoracic spinal cord injury and chronic constriction injury of the sciatic nerve. Pitting the combined motivations to avoid the bright light and to explore the novel device against pain from crossing noxious probes disclosed a conflicting, hyperalgesia-related reluctance to repeatedly cross the probes after injury. Rats receiving standard sham surgeries demonstrated enhanced pain-like avoidance behavior compared with naive controls, and this behavior was similar to that of corresponding chronic constriction injury or spinal cord injury rats weeks or months after injury. In the case of sham surgery for spinal cord injury, video analysis of voluntary exploratory behavior directed at the probes revealed enhanced forepaw withdrawal responses. These findings have important implications for preclinical investigations into behavioral alterations and physiological mechanisms associated with postsurgical and neuropathic pain.

Are There Multiple Motivators for Helping Behavior in Rats?

Empathy is the ability to (a) be affected by and share the emotional state of another; (b) assess the reasons for the other’s state; and (c) identify with the other, adopting their perspective. This phenomenon has been shown to exist in several species and is proposed as a motivator for prosocial behavior. The experimental study of this feature in laboratory rodents is a more viable alternative in comparison to wild animals. A recent report showed that rats opened a door to free their cage mate from a restraint box. Although this behavior has been suggested to be motivated by empathy, this fact has been questioned by several studies that proposed other motivators for the releasing behavior. In the present study, we use an adaptation of the protocol of releasing behavior to investigate aspects of empathy and pro-sociality such as familiarity and reciprocity. In addition, we addressed some potential motivational factors that could influence this behavior. The main results showed that (1) rats opened the restraint box to free conspecifics most of the time; (2) direct reciprocity or past restriction experience did not improve releasing performance, probably due to a ceiling effect; (3) after a series of trials in the presence of a restricted conspecific, the free rat continues to open the restraint box even if it is empty; (4) in general, the opening performance improves across trials and phases, resembling learning curves; (5) if the first series of trials occurs with the empty box, the opening behavior does not occur and is modest in subsequent trials with a trapped animal; (6) the exploratory drive toward the restraint box and desire for social contact do not seem to function as key motivators for releasing behavior. In conclusion, our findings do not support that the opening behavior is exclusively related to empathic motivation. While multiple factors might be involved, our study suggests that task learning triggered (and possibly reinforced) by the presence of the restricted rat can function as a motivator. Further investigations are required to fully understand the mechanisms and motivation factors guiding the releasing behavior.

A Go/No-go delayed nonmatching-to-sample procedure to measure object-recognition memory in rats

The novel-object preference (NOP) test is widely used to assess object-recognition memory in rats. When interpreting behaviour on the test, a common assumption is that the magnitude of a rat's novel-object preference reflects the persistence or accuracy of its memory for the previously encountered object. However, some concerns have been raised regarding the latter interpretation, and hence, the internal validity of the NOP test as a gauge of object-recognition abilities. Given the concerns, we developed a new Go/No-go delayed nonmatching-to-sample (DNMS) procedure to measure object-recognition memory, which circumvents the interpretational problems associated with the NOP test. Rats were trained to displace an unfamiliar object (sample) from over a food well to obtain a food reward. Then on a choice phase, rats were presented with novel objects ("Go" trial) or copies of the sample object ("No-go" trial). On Go trials rats received a reward for displacing the novel object and on No-go trials no reward was provided for displacing the sample object. Rats required an average 54 sessions to reach a performance criterion of at least 80 % correct choices on five consecutive sessions (16 correct choices out of 20). Afterwards, rats were tested on the NOP test, and we found that scores on both tasks were not significantly correlated, indicating performance on the Go/No-go DNMS task did not predict novelty preference scores. The findings from this experiment reveal the benefits of an alternative approach to assess object-recognition memory in rats.

Morphological Correlates of Personality in Female Asian Particolored Bats (Vespertilio sinensis)

Simple Summary

Personality emerges because of individual differences in repeatable state variables, such as metabolic rate, age, sex, or body size. Personality and its correlation with body size, however, have been relatively unexplored in bats. Our study showed that the exploration of female Asian particolored bats was significantly repeatable, but we did not find significant correlations among exploration, activity, and aggression. This finding suggested that female Asian particolored bats may not have a behavioral syndrome. Additionally, the body mass of female Asian particolored bats was correlated with aggression and activity, suggesting that body mass may have an impact on the behavioral characteristics of bats. Our findings not only added to the literature concerning personality in bats but are also helpful for understanding the maintenance of an animal’s personality.

Abstract

Personality traits represent a leading edge in the evolutionary process, as natural selection acts directly on variations in individual phenotypes within populations. Recent theoretical models have focused on the concept of adaptive state-dependent behavior, proposing that repeatable differences in behavior emerge because of individual differences in repeatable state variables, such as metabolic rate, age, sex, or body size. Personality and its correlation with body size, however, have been relatively unexplored in bats. We used female Asian particolored bats (Vespertilio sinensis) to investigate three personality characteristics (exploration, activity, and aggression) using the classic hole-board test and examined their relationships with body size using an information-theoretical approach. Our results showed that the exploration of female Asian particolored bats was significantly repeatable, but we did not find significant correlations among the three personality traits. This finding suggested that the female Asian particolored bat may not have a behavioral syndrome. In addition, the body mass of female Asian particolored bats was positively correlated with aggression but was negatively correlated with activity, suggesting that body mass was an important physiological basis affecting the behavioral characteristics of female Asian particolored bats.

Time allocation to resources by three species of rats (Rattus spp.) in a radial arm maze

Abstract ContextIntroduced rats (Rattus spp.) can pose a serious threat to native flora and fauna, especially on islands where most species have evolved in the absence of terrestrial predators. Effective detection and eradication methods for introduced rats are essential to the maintenance of insular ecosystem integrity. Thus, it is important to better understand the behaviour of rats when they first arrive in a new setting. AimsTo determine whether rats would find some novel stimuli to be significantly more attractive than other novel stimuli. MethodsAn eight-arm radial maze was used to study the behaviour of three species of Rattus finding themselves in a novel environment with various familiar and unfamiliar stimuli. Key resultsAlthough there were some differences in responses by species and by sex, most rats sought out and spent considerable time in the den box, suggesting an immediate need for security when in an unfamiliar setting. Rats also sought out faeces of conspecifics, suggesting the need for social contact or reproduction. The rats, which had not been food deprived, did not seem interested in food sources, although there was some attraction to the water source. ImplicationsThe management implications of the present study’s results are two-fold. First, appears that detection of newly arriving rats on islands would be aided by strategic placement of den boxes that are highly acceptable to rats. Managers could then inspect the den boxes periodically (or use a remote sensing system) for evidence of rat presence. Second, the den boxes could be scented with the faeces of other rats to further attract invading rats to the den boxes. This protocol might also hold the rats near the invasion site for a longer period of time before they begin seeking other shelter, food sources or mates. These protocols could give managers increased opportunities to detect any newly invading rats, and potentially increase the available time to deploy a rapid response to the invasion, before the animals begin to widely disperse. Of course, the rats will ultimately seek a source of palatable food, so placing durable, yet palatable, rodenticide bait in the den boxes might further decrease the probability of the invaders establishing a self-sustaining population.

Effects of perirhinal cortex and hippocampal lesions on rats' performance on two object-recognition tasks

The effects of hippocampal (HPC) damage on rats' novel object preference (NOP) performance have been rather consistent, in that HPC lesions do not disrupt novelty preferences on the test. Conversely, there have been inconsistent findings regarding the effects of perirhinal cortex (PRh) lesions on rats' novel-object preferences. Given the concerns that have been raised regarding the internal validity of the NOP test, viz. that the magnitude of the novel-object preference does not necessarily reflect the strength in memory for an object, it could explain the discrepant findings. The goal of the present experiment was to examine the effects of PRh and HPC lesions on rats' object-recognition memory using a new modified delayed nonmatching-to-sample (mDNMS) task, as it circumvents the interpretational problems associated with the NOP test. Rats received PRh, HPC, or Sham lesions and were trained on the mDNMS task using a short delay (∼30 s). Both PRh and HPC rats acquired the task at the same rate as Sham rats, and reached a similar level of accuracy, indicating intact object-recognition. Thereafter, rats were tested on the NOP test using a 180-s delay. Rats with HPC lesions exhibited significant novel-object preferences, however, both the PRh and Sham rats failed to show a novelty preference. The discrepancy in both the PRh and Sham rats' performance on the mDNMS task and NOP test raises concerns regarding the internal validity of the NOP test, in that the magnitude of a rat's novel-object preference does not accurately reflect the persistence or accuracy of a rat's memory for the sample object.

Water games by mountain gorillas: implications for behavioral development and flexibility-a case report

Functions of play, which may be performed solo or in a social context, include motor training and behavioral flexibility. Play is often more common in infancy and the juvenile period, although it also occurs in adults of many species. In contrast to social play, few studies have investigated solitary play. Here, we present new empirical data on solitary water play in a subadult and two adult mountain gorillas in Bwindi Impenetrable National Park, Uganda, observed on three different days between January and February 2018. Focal sampling was used to record the behavior of the individuals interacting with water. Movements included vigorous rotation of the arms, splashing the water, tilting the head, making a play face, and sweeping with the hands to create waves on the water surface. One of the episodes represents the first vigorous display of splashing water ever reported for Bwindi gorillas. Our observations highlight three significant components of mountain gorilla development and behavior: play, behavioral flexibility, and exploration.

Episodic curiosity for avoiding asteroids: Per-trial information gain for choice outcomes drive information seeking

Humans often appear to desire information for its own sake, but it is presently unclear what drives this desire. The important role that resolving uncertainty plays in stimulating information seeking has suggested a tight coupling between the intrinsic motivation to gather information and performance gains, construed as a drive for long-term learning. Using an asteroid-avoidance game that allows us to study learning and information seeking at an experimental time-scale, we show that the incentive for information-seeking can be separated from a long-term learning outcome, with information-seeking best predicted by per-trial outcome uncertainty. Specifically, participants were more willing to take time penalties to receive feedback on trials with increasing uncertainty in the outcome of their choices. We found strong group and individual level support for a linear relationship between feedback request rate and information gain as determined by per-trial outcome uncertainty. This information better reflects filling in the gaps of the episodic record of choice outcomes than long-term skill acquisition or assessment. Our results suggest that this easy to compute quantity can drive information-seeking, potentially allowing simple organisms to intelligently gather information for a diverse episodic record of the environment without having to anticipate the impact on future performance.

Positive Welfare for Fishes: Rationale and Areas for Future Study

Traditional animal welfare paradigms have focused on maintaining physical health and mitigating negative impacts to wellbeing. Recently, however, the field has increasingly recognized the importance of positive welfare (i.e., mental and physical states that exceed what is necessary for immediate survival) and accordingly introduced manipulations and indicators of positive welfare for use in agriculture, laboratories, and zoos/aquaria. The creation and monitoring of positive welfare requires an in-depth knowledge of species-specific behavior and biology, which necessitates species-specific or, at a minimum, taxa-specific standards. Research on positive welfare in fish is lagging in this regard and therefore merits further consideration. In this paper, we aim to merge what is already known about positive welfare with the existing fish behavior literature to develop a plan of action for fish welfare research that will ultimately contribute to the development of positive welfare standards and assessment strategies for fish. We begin by exploring the origins of positive welfare research and then outline the physical, psychological and species-specific areas of inquiry that can be investigated in fish. In addition to presenting current findings on fish motivation, emotion, potential sources of positive welfare such as fulfillment of motivational urges (establishing agency, engaging in exploration and learning), and play behavior, we also identify promising areas for future research aimed at developing accurate and appropriate indicators of positive welfare in fish.

Anxiety and exploratory behavior in the African striped mouse, Rhabdomys, taxa are partially modified by the physical rearing environment

The environment may modulate genetic influences on behavioral expression. We investigated whether the physical rearing environment modulates anxiety and exploratory behavior in four populations, representing three species, of the striped mouse Rhabdomys. One population originated from an arid, open habitat and the others from grassy, covered habitats, and two species occurred in sympatry. We raised captive individuals of all populations in treatments that simulated cover or no cover for two generations and investigated the behavior of resulting adults in an open-field, light-dark and startle response tests. We expected that, when raised without cover, the arid population would be less anxious and more exploratory than grassland populations, but found the opposite in the open-field test only. We also expected that all individuals would be anxious and less exploratory when raised under cover, which was the case for anxiety in a light-dark test, but individuals from the no cover treatment were more anxious in the open-field test. Only one population × treatment interaction was detected in which the arid population was least exploratory. Therefore, the physical rearing environment had less of an influence than phylogeny on the development of anxiety and exploration in Rhabdomys.

Is Heightened-Shoaling a Good Candidate for Positive Emotional Behavior in Zebrafish?

Simple Summary

Despite increasing interest in fish welfare, we still know very little about positive emotions in fish. This study had two aims: (1) to characterize a previously undescribed social behavior in zebrafish, “heightened-shoaling”, and (2) to evaluate whether heightened-shoaling may be a good candidate for future research into positive emotional behavior in zebrafish. Observing six groups of zebrafish housed in 110 L tanks furnished with a sloping gravel substrate, rocks, and artificial plants (10 fish/tank), we found that heightened-shoaling is marked by tight group cohesion, high behavioral synchrony (all fish engaging in the same behaviors at the same time), and low agonism. Episodes of heightened-shoaling occurred in all six groups, but rarely at the same time (only once out of 31 episodes), suggesting that the onset of heightened-shoaling is driven by internal group dynamics rather than external influences. Heightened-shoaling also appeared to be self-reinforcing as it had sustained durations—typically lasting for over 7 min and sometimes lasting for nearly half-an-hour. Collectively, these results are similar to the patterns that typify positive emotional behavior in other animals, for example, social grooming and social play. As the first description of heightened-shoaling, this research extends our knowledge of the range of zebrafish social dynamics and suggests a promising area for future research on positive emotions in fish.

Abstract

Zebrafish, a highly-social species of freshwater fish, are widely studied across many fields of laboratory science including developmental biology, neuroscience, and genomics. Nevertheless, as standard housing for zebrafish typically consists of small and simplistic environments, less is known about their social behavioral repertoire in more naturalistic settings. In particular, spontaneously occurring, socio-positive affiliative behaviors (e.g., social coordination and cohesion) that may be indicative of positive emotional experiences have rarely been reported or studied deliberately in zebrafish. Housing adult zebrafish (10 fish/tank) in large semi-natural tanks (110 L; n = 6) with sloping gravel substrate, rocks, and artificial plants, we observed a previously undescribed behavior: Distinct periods of spontaneous, synchronized, compact aggregations, what we call “heightened-shoaling”. This project aimed to quantify the characteristics of this distinctive behavior and compare parameters of heightened-shoaling to baseline periods (normal behavior) and pre-feed periods (feed-anticipatory behavior). First, across 4 days, we selected video-clips (100 s each) from within (i) instances of heightened-shoaling (n = 9), (ii) baseline periods (n = 18), and (iii) pre-feed periods (n = 18). For each of these video clips, we scan sampled every 10 s to determine fish orientations and location within the tank and agonistic behavior. Next, we used an all-occurrence sampling method to record the timing and duration of all episodes of heightened-shoaling behavior when tank-lights were on (8:00 h to 18:00 h) across 10 days. From the scan-sampling data, we found that compared to baseline periods, heightened-shoaling was characterized by increased shoal cohesion (p < 0.0001), increased adherence to the horizontal plane (p < 0.0001), decreased agonism (p < 0.0001), and no diving behavior (lower positions within the water column signal negative effect in zebrafish, p > 0.1). From the all-occurrence sampling data, we found 31 episodes of heightened-shoaling with instances observed in all six tanks and only a single case in which heightened-shoaling occurred in two tanks at the same time. The median episode duration was 7.6 min (Range 1.3–28.6). As the first systematic description of heightened-shoaling behavior, this research contributes to our knowledge of the range of zebrafish social dynamics living in naturalistic environments. Moreover, as a spontaneously occurring, protracted, affiliative behavior, heightened-shoaling appears to be a good candidate for future research into positive emotional behavior in zebrafish.

Does Enrichment Improve Well Being in Animals under Human Care? A Case Study of Two Harbor Seals (Phoca Vitulina)

Harbor seals in the wild live in a stimulating environment; therefore, nonhuman-animal caretakers have increasingly been using environmental enrichment to improve the well being of seals under human care. The purpose of this study was to evaluate an object-based environmental enrichment program during a four-month period on stimulating exploration and play and improving conspecific social interactions and human-animal relationships (HAR). Zoo staff conducted the environmental enrichment program as part of the animal care program. Seals were given objects haphazardly and were observed for 20 minutes, and seals' responsiveness during training sessions before and after enrichment was assessed. Seals showed interest in objects throughout the study and interacted more times per session with objects during the later months. Seals showed preferences for objects that were suspended in the water column (e.g., rope). Seals did not show more affiliative behavior but did show some aggressive behavior during enrichment sessions in comparison with free-swimming sessions. One seal showed better responsiveness to trainers in training sessions that followed an enrichment session than in other trainings sessions. Overall, the enrichment program was successful in increasing intrinsically motivated behaviors and showed that object-based enrichment has the potential to improve HAR between seals and their trainers.

Objective assessment of exploratory behaviour in schizophrenia using wireless motion capture

Motivation deficits are a prominent feature of schizophrenia and have substantial consequences for functional outcome. The impact of amotivation on exploratory behaviour has not been extensively assessed by entirely objective means. This study evaluated deficits in exploratory behaviour in an open-field setting using wireless motion capture. Twenty-one stable adult outpatients with schizophrenia and twenty matched healthy controls completed the Novelty Exploration Task, in which participants explored a novel environment containing familiar and uncommon objects. Objective motion data were used to index participants' locomotor activity and tendency for visual and tactile object exploration. Clinical assessments of positive and negative symptoms, apathy, cognition, depression, medication side-effects, and community functioning were also administered. Relationships between task performance and clinical measures were evaluated using Spearman correlations, and group differences were evaluated using multivariate analysis of covariance tests. Although locomotor activity and tactile exploration were similar between the schizophrenia and healthy control groups, schizophrenia participants exhibited reduced visual object exploration (F(2,35)=3.40, p=0.045). Further, schizophrenia participants' geometric pattern of locomotion, visual exploration, and tactile exploration were correlated with overall negative symptoms (|ρ|=0.46-0.64, p<=0.039) and apathy (|ρ|=0.49-0.62, p<=0.028), and both visual and tactile exploration were also correlated with community functioning (|ρ|=0.46-0.48, p<=0.043). The Novelty Exploration Task may be a valuable tool to quantify exploratory behaviour beyond what is captured through standard clinical instruments and human observer ratings. Findings from this initial study suggest that locomotor activity and object interaction tendencies are impacted by motivation, and reveal deficits specifically in visual exploration in schizophrenia.

Disentangling the Role of the MEC and LEC in the Processing of Spatial and Non-Spatial Information: Contribution of Lesion Studies

It is now widely accepted that the entorhinal cortex (EC) plays a pivotal role in the processing of spatial information and episodic memory. The EC is segregated into two sub-regions, the medial EC (MEC) and the lateral EC (LEC) but a comprehensive understanding of their roles across multiple behavioral contexts remains unclear. Considering that it is still useful to investigate the impact of lesions of EC on behavior, we review the contribution of lesion approach to our knowledge of EC functions. We show that the MEC and LEC play different roles in the processing of spatial and non-spatial information. The MEC is necessary to the use of distal but not proximal landmarks during navigation and is crucial for path integration, in particular integration of linear movements. Consistent with predominant hypothesis, the LEC is important for combining the spatial and non-spatial aspects of the environment. However, object exploration studies suggest that the functional segregation between the MEC and the LEC is not as clearly delineated and is dependent on environmental and behavioral factors. Manipulation of environmental complexity and therefore of cognitive demand shows that the MEC and the LEC are not strictly necessary to the processing of spatial and non-spatial information. In addition we suggest that the involvement of these sub-regions can depend on the kind of behavior, i.e., navigation or exploration, exhibited by the animals. Thus, the MEC and the LEC work in a flexible manner to integrate the “what” and “where” information in episodic memory upstream the hippocampus.