Challenges and advanced concepts for the assessment of learning and memory function in mice

The mechanisms underlying the formation and retrieval of memories are still an active area of research and discussion. Manifold models have been proposed and refined over the years, with most assuming a dichotomy between memory processes involving non-conscious and conscious mechanisms. Despite our incomplete understanding of the underlying mechanisms, tests of memory and learning count among the most performed behavioral experiments. Here, we will discuss available protocols for testing learning and memory using the example of the most prevalent animal species in research, the laboratory mouse. A wide range of protocols has been developed in mice to test, e.g., object recognition, spatial learning, procedural memory, sequential problem solving, operant- and fear conditioning, and social recognition. Those assays are carried out with individual subjects in apparatuses such as arenas and mazes, which allow for a high degree of standardization across laboratories and straightforward data interpretation but are not without caveats and limitations. In animal research, there is growing concern about the translatability of study results and animal welfare, leading to novel approaches beyond established protocols. Here, we present some of the more recent developments and more advanced concepts in learning and memory testing, such as multi-step sequential lockboxes, assays involving groups of animals, as well as home cage-based assays supported by automated tracking solutions; and weight their potential and limitations against those of established paradigms. Shifting the focus of learning tests from the classical experimental chamber to settings which are more natural for rodents comes with a new set of challenges for behavioral researchers, but also offers the opportunity to understand memory formation and retrieval in a more conclusive way than has been attainable with conventional test protocols. We predict and embrace an increase in studies relying on methods involving a higher degree of automatization, more naturalistic- and home cage-based experimental setting as well as more integrated learning tasks in the future. We are confident these trends are suited to alleviate the burden on animal subjects and improve study designs in memory research.

Socio-ecological correlates of neophobia in corvids

Behavioral responses to novelty, including fear and subsequent avoidance of novel stimuli, i.e., neophobia, determine how animals interact with their environment. Neophobia aids in navigating risk and impacts on adaptability and survival. There is variation within and between individuals and species; however, lack of large-scale, comparative studies critically limits investigation of the socio-ecological drivers of neophobia. In this study, we tested responses to novel objects and food (alongside familiar food) versus a baseline (familiar food alone) in 10 corvid species (241 subjects) across 10 labs worldwide. There were species differences in the latency to touch familiar food in the novel object and novel food conditions relative to the baseline. Four of seven socio-ecological factors influenced object neophobia: (1) use of urban habitat (versus not), (2) territorial pair versus family group sociality, (3) large versus small maximum flock size, and (4) moderate versus specialized caching (whereas range, hunting live animals, and genus did not), while only maximum flock size influenced food neophobia. We found that, overall, individuals were temporally and contextually repeatable (i.e., consistent) in their novelty responses in all conditions, indicating neophobia is a stable behavioral trait. With this study, we have established a network of corvid researchers, demonstrating potential for further collaboration to explore the evolution of cognition in corvids and other bird species. These novel findings enable us, for the first time in corvids, to identify the socio-ecological correlates of neophobia and grant insight into specific elements that drive higher neophobic responses in this avian family group. VIDEO ABSTRACT.

Social Reward and Empathy as Proximal Contributions to Altruism: The Camaraderie Effect

Natural selection favors individuals to act in their own interests, implying that wild animals experience a competitive psychology. Animals in the wild also express helping behaviors, presumably at their own expense and suggestive of a more compassionate psychology. This apparent paradox can be partially explained by ultimate mechanisms that include kin selection, reciprocity, and multilevel selection, yet some theorists argue such ultimate explanations may not be sufficient and that an additional "stake in others" is necessary for altruism's evolution. We suggest this stake is the "camaraderie effect," a by-product of two highly adaptive psychological experiences: social motivation and empathy. Rodents can derive pleasure from access to others and this appetite for social rewards motivates individuals to live together, a valuable psychology when group living is adaptive. Rodents can also experience empathy, the generation of an affective state more appropriate to the situation of another compared to one's own. Empathy is not a compassionate feeling but it has useful predictive value. For instance, empathy allows an individual to feel an unperceived danger from social cues. Empathy of another's stance toward one's self would predict either social acceptance or ostracism and amplify one's physiological sensitivity to social isolation, including impaired immune responses and delayed wound healing. By contrast, altruistic behaviors would promote well-being in others and feelings of camaraderie from others, thereby improving one's own physiological well-being. Together, these affective states engender a stake in others necessary for the expression of altruistic behavior.

The influence of relationships on neophobia and exploration in wolves and dogs

Exploration is important for animals to be able to gather information about features of their environment that may directly or indirectly influence survival and reproduction. Closely related to exploration is neophobia, which may reduce exposure to danger, but also constrain explorative behaviour. Here we investigated the effects of social relationships on neophobia and exploration in wolves, Canis lupus, and dogs, Canis familiaris. Eleven pack-living wolves reared by human foster parents and 13 identically raised and kept dogs were tested in a novel object test under three different conditions: (1) alone, (2) paired with a pack mate and (3) together with the entire pack. Dogs were less neophobic than wolves and interacted faster with the novel objects. However, the dogs showed overall less interest in the novel objects than wolves, which investigated the objects for longer than the dogs. Both wolves and dogs manipulated objects for longer when paired or in the pack than when alone. While kinship facilitated the investigation of novel objects in the pair condition in both wolves and dogs, rank distance had opposite effects. Our results suggest that the presence of conspecifics supported the exploration of novel objects in both wolves and dogs, particularly within kin and that this may be interpreted as risk sharing. The reduced latency to approach objects and less time spent exploring objects in dogs compared to wolves may be interpreted as an effect of domestication.

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We tested neophobia and exploration in dogs and wolves.

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Dogs were quicker to approach, but showed less interest in, novel objects.

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Presence of conspecifics enhanced approaches to, and exploration of, novel objects.

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Our findings suggest risk sharing mediates cooperation in wolves and dogs.

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We assume the differences between wolves and dogs to be an effect of domestication.

Witnessing traumatic events causes severe behavioral impairments in rats

Witnessing a traumatic event but not directly experiencing it can be psychologically quite damaging. In North America alone, ∼30% of individuals who witness a traumatic event develop post-traumatic stress disorder (PTSD). While effects of direct trauma are evident, consequences of indirect or secondary trauma are often ignored. Also unclear is the role of social support in the consequences of these experiences. The social defeat paradigm, which involves aggressive encounters by a large Long-Evans male rat (resident) towards a smaller Sprague-Dawley male rat (intruder), is considered a rodent model of PTSD. We have modified this model to create a trauma witness model (TWM) and have used our TWM model to also evaluate social support effects. Basically, when an intruder rat is placed into the home cage of a resident rat, it encounters an agonistic behavior resulting in intruder subordination. The socially defeated intruder is designated the SD rat. A second rat, the cage mate of the SD, is positioned to witness the event and is the trauma witnessing (TW) rat. Experiments were performed in two different experimental conditions. In one, the SD and TW rats were cagemates and acclimatized together. Then, one SD rat was subjected to three sessions of social defeat for 7 d. TW rat witnessed these events. After each social defeat exposure, the TW and SD rats were housed together. In the second, the TW and SD rats were housed separately starting after the first defeat. At the end of each protocol, depression-anxiety-like behavior and memory tests were conducted on the SD and TW rats, blood withdrawn and specific organs collected. Witnessing traumatic events led to depression- and anxiety-like behavior and produced memory deficits in TW rats associated with elevated corticosterone levels.

Estrogenic involvement in social learning, social recognition and pathogen avoidance

Sociality comes with specific cognitive skills that allow the proper processing of information about others (social recognition), as well as of information originating from others (social learning). Because sociality and social interactions can also facilitate the spread of infection among individuals the ability to recognize and avoid pathogen threat is also essential. We review here various studies primarily from the rodent literature supporting estrogenic involvement in the regulation of social recognition, social learning (socially acquired food preferences and mate choice copying) and the recognition and avoidance of infected and potentially infected individuals. We consider both genomic and rapid estrogenic effects involving estrogen receptors α and β, and G-protein coupled estrogen receptor 1, along with their interactions with neuropeptide systems in the processing of social stimuli and the regulation and expression of these various socially relevant behaviors.

Rodent empathy and affective neuroscience

In the past few years, several experimental studies have suggested that empathy occurs in the social lives of rodents. Thus, rodent behavioral models can now be developed to elucidate the mechanistic substrates of empathy at levels that have heretofore been unavailable. For example, the finding that mice from certain inbred strains express behavioral and physiological responses to conspecific distress, while others do not, underscores that the genetic underpinnings of empathy are specifiable and that they could be harnessed to develop new therapies for human psychosocial impairments. However, the advent of rodent models of empathy is met at the outset with a number of theoretical and semantic problems that are similar to those previously confronted by studies of empathy in humans. The distinct underlying components of empathy must be differentiated from one another and from lay usage of the term. The primary goal of this paper is to review a set of seminal studies that are directly relevant to developing a concept of empathy in rodents. We first consider some of the psychological phenomena that have been associated with empathy, and within this context, we consider the component processes, or endophenotypes of rodent empathy. We then review a series of recent experimental studies that demonstrate the capability of rodents to detect and respond to the affective state of their social partners. We focus primarily on experiments that examine how rodents share affective experiences of fear, but we also highlight how similar types of experimental paradigms can be utilized to evaluate the possibility that rodents share positive affective experiences. Taken together, these studies were inspired by Jaak Panksepp's theory that all mammals are capable of felt affective experiences.

Empathy is moderated by genetic background in mice

Empathy, as originally defined, refers to an emotional experience that is shared among individuals. When discomfort or alarm is detected in another, a variety of behavioral responses can follow, including greater levels of nurturing, consolation or increased vigilance towards a threat. Moreover, changes in systemic physiology often accompany the recognition of distressed states in others. Employing a mouse model of cue-conditioned fear, we asked whether exposure to conspecific distress influences how a mouse subsequently responds to environmental cues that predict this distress. We found that mice are responsive to environmental cues that predict social distress, that their heart rate changes when distress vocalizations are emitted from conspecifics, and that genetic background substantially influences the magnitude of these responses. Specifically, during a series of pre-exposure sessions, repeated experiences of object mice that were exposed to a tone-shock (CS-UCS) contingency resulted in heart rate deceleration in subjects from the gregarious C57BL/6J (B6) strain, but not in subjects from the less social BALB/cJ (BALB) strain. Following the pre-exposure sessions, subjects were individually presented with the CS-only for 5 consecutive trials followed by 5 consecutive pairings of the CS with the UCS. Pre-exposure to object distress increased the freezing responses of B6 mice, but not BALB mice, on both the CS-only and the CS-UCS trials. These physiological and behavioral responses of B6 mice to social distress parallel features of human empathy. Our paradigm thus has construct and face validity with contemporary views of empathy, and provides unequivocal evidence for a genetic contribution to the expression of empathic behavior.

Novel object exploration in ravens (Corvus corax): Effects of social relationships

Social context has been shown to encourage, or to delay object exploration and learning. This ambiguity might be due to factors such as social relationships and personality of the individuals involved. Here, we investigated in ravens (Corvus corax) individuals' consistency in response to novel objects over development and across contexts: alone versus social. In the social setting we focussed on the effects of social relationships on social facilitation during the approach to novel objects. We tested 11 hand-raised ravens with novel objects individually at three and six months of age and in dyadic combinations at six months of age. Individuals were consistent over development and contexts in their response to different novel objects. Birds joined siblings faster to approach novel objects than non-siblings. They also spent more time sitting close to siblings than to non-siblings. In male-male dyads but not in female-female dyads, subordinates approached the novel objects significantly faster than dominant birds. In contrast, dominant males were the first to approach the novel objects in mixed-sex combinations. Hence, the effect of social context seems to depend on the social relationships towards the companions and on the combination of the sexes.