Social housing enhances acquisition of task set independently of environmental enrichment: A longitudinal study in the Barnes maze

A bibliometric analysis of studies on environmental enrichment spanning 1967-2024: patterns and trends over the years

Environmental Enrichment (EE) has received considerable attention for its potential to enhance cognitive and neurobiological outcomes in animal models. This bibliometric analysis offers a comprehensive evaluation of the EE research spanning from 1967 to 2024, utilizing data extracted from Scopus and analyzed through R and VOSviewer. The volume of publications, citation patterns, and collaborations were systematically reviewed, highlighting important contributions and emerging trends within the field of animal research. Core concepts of EE research are mapped, revealing key themes such as neuroplasticity, cognitive function, and behavioral outcomes. A significant increase in EE research is demonstrated, particularly after the year 2000, reflecting growing scientific and public interest in EE paradigms. This analysis provides insights into the global contributions and collaborative networks that have shaped EE studies over time. The role of EE in advancing the understanding of neurobiological, neurodevelopmental, and neurodegenerative processes is underscored. Influential contributors, leading countries, and high-impact journals in the field of EE are identified, offering a valuable resource for researchers seeking to understand or extend the current knowledge base. The strategic selection of keywords and rigorous data curation methods ensure that the findings accurately reflect the most impactful aspects of EE research in animals. This study serves as an essential reference for future explorations and applications of EE across disciplines. By providing a clear and structured overview of the field, this paper aims to serve as a foundation for ongoing and future research initiatives, encouraging more robust investigations and applications of EE to enhance cognitive and neurological health globally.

Meta-analyses reveal support for the Social Intelligence Hypothesis

The Social Intelligence Hypothesis (SIH) is one of the leading explanations for the evolution of cognition. Since its inception a vast body of literature investigating the predictions of the SIH has accumulated, using a variety of methodologies and species. However, the generalisability of the hypothesis remains unclear. To gain an understanding of the robustness of the SIH as an explanation for the evolution of cognition, we systematically searched the literature for studies investigating the predictions of the SIH. Accordingly, we compiled 103 studies with 584 effect sizes from 17 taxonomic orders. We present the results of four meta-analyses which reveal support for the SIH across interspecific, intraspecific and developmental studies. However, effect sizes did not differ significantly between the cognitive or sociality metrics used, taxonomy or testing conditions. Thus, support for the SIH is similar across studies using neuroanatomy and cognitive performance, those using broad categories of sociality, group size and social interactions, across taxonomic groups, and for tests conducted in captivity or the wild. Overall, our meta-analyses support the SIH as an evolutionary and developmental explanation for cognitive variation.

Using Appetitive Motivation to Train Mice for Spatial Learning in the Barnes Maze

The Barnes maze, a well-known spatial-learning paradigm, is based on the innate fear of rodents of large open spaces and their drive to hide. However, additional aversive stimuli (strong light and threatening sounds) are often necessary to provoke the hiding response while rendering the method cumbersome and more stressful. Our objective was to establish a Barnes maze-learning paradigm in mice using palatable food as a reward. After habituating male C57BL6/J or NMRI mice to the reward, the experimenter and the apparatus, either a slow (2 trials/day) or a massive conditioning schedule (4 trials/day), was run. Acquisition training was carried out until mice could locate the reward box with a maximum of one hole error. Then, the box was replaced to another location (reversal phase). Mice needed to relearn the new position with the same criterion. One week later, retention trials were performed. Both strains could reach the learning criteria; in the massive training within a shorter period. Spatial memory was demonstrated in the reversal and retention trials. Our results show that palatable food can be used as an efficient motivator to acquire allocentric navigation in the Barnes maze with the additional advantage of being less stressful.

Environmental modifications to rehabilitate social behavior deficits after acquired brain injury: What is the evidence?

Social behavior deficits are a common, debilitating consequence of traumatic brain injury and stroke, particularly when sustained during childhood. Numerous factors influence the manifestation of social problems after acquired brain injuries, raising the question of whether environmental manipulations can minimize or prevent such deficits. Here, we examine both clinical and preclinical evidence addressing this question, with a particular focus on environmental enrichment paradigms and differing housing conditions. We aimed to understand whether environmental manipulations can ameliorate injury-induced social behavior deficits. In summary, promising data from experimental models supports a beneficial role of environmental enrichment on social behavior. However, limited studies have considered social outcomes in the chronic setting, and few studies have addressed the social context specifically as an important component of the post-injury environment. Clinically, limited high-caliber evidence supports the use of specific interventions for social deficits after acquired brain injuries. An improved understanding of how the post-injury environment interacts with the injured brain, particularly during development, is needed to validate the implementation of rehabilitative interventions that involve manipulating an individuals' environment.

Sex- and age-dependent contribution of System xc- to cognitive, sensory, and social behaviors revealed by comprehensive behavioral analyses of System xc- null mice

Background

System xc- (Sxc-) is an important heteromeric amino acid cystine/glutamate exchanger that plays a pivotal role in the CNS by importing cystine into cells while exporting glutamate. Although certain behaviors have been identified as altered in Sxc- null mutant mice, our understanding of the comprehensive impact of Sxc- on behavior remains incomplete.

Methods

To address this gap, we compared motor, sensory and social behaviors of male and female mice in mice null for Sxc- (SLC7A11sut/sut) with wildtype littermates (SLC7A11+/+) in a comprehensive and systematic manner to determine effects of genotype, sex, age, and their potential interactions.

Results

Motor performance was not affected by loss of Sxc- in both males and females, although it was impacted negatively by age. Motor learning was specifically disrupted in female mice lacking Sxc- at both 2 and 6 months of age. Further, female SLC7A11sut/sut mice at both ages exhibited impaired sociability, but normal spatial and recognition memory, as well as sensorimotor gating. Finally, pronounced open-space anxiety was displayed by female SLC7A11sut/sut when they were young. In contrast, young SLC7A11sut/sut male mice demonstrated normal sociability, delayed spatial learning, increased open-space anxiety and heightened sensitivity to noise. As they aged, anxiety and noise sensitivity abated but hyperactivity emerged.

Discussion

We find that the behavioral phenotypes of female SLC7A11sut/sut are similar to those observed in mouse models of autism spectrum disorder, while behaviors of male SLC7A11sut/sut resemble those seen in mouse models of attention deficit hyperactivity disorder. These results underscore the need for further investigation of SLC7A11 in neurodevelopment. By expanding our understanding of the potential involvement of Sxc-, we may gain additional insights into the mechanisms underlying complex neurodevelopmental conditions.

An updated Barnes maze protocol for assessing the outcome of controlled cortical impact mouse models of traumatic brain injury

BACKGROUND

The Barnes Maze (BM) is a common method of testing cognitive deficits in rodents. Adapting BM protocols for specific neurological disorders could potentially aid in more effective testing, reduce research time, and help decrease variability between studies.

NEW METHOD

We tested differences an updated, shortened BM consisting of 6 days, 3 trials per day, only covering the equivalent of the spatial acquisition week BM protocol and a probe trial day consisting of one trial (7 total days).

RESULTS

Kaplan-Meier plots of escape percentage as a function of total latency showed a significant difference between control and CCI mice in the updated protocol on days 3 through 6. Additionally, probe trial data showed significant differences in primary latency, primary errors, and returns to goal.

COMPARISON WITH EXISTING METHODS

We tested differences between a traditional 5 days per week, 2 trials per day, spatial acquisition and reversal weeks BM protocol (12 total days with probe trials) with an updated 6-day BM protocol (7 total days with probe trial). In the probe trial, the updated protocol control mice showed an over 5-fold decrease in primary latency and primary errors and a 4.6-fold increase in returns to goal compared to the traditional protocol. Additionally, mice in both protocols performed similarly on a trial-by-trial basis suggesting that the changes made for the updated protocol increased learning and memory and was not simply an easier task.

CONCLUSION

The updated BM protocol showed an improved ability to distinguish between control and CCI mice and promoted improved and more consistent learning for both the control and CCI groups.

Areas of Convergence and Divergence in Adolescent Social Isolation and Binge Drinking: A Review

Adolescence is a critical developmental period characterized by enhanced social interactions, ongoing development of the frontal cortex and maturation of synaptic connections throughout the brain. Adolescents spend more time interacting with peers than any other age group and display heightened reward sensitivity, impulsivity and diminished inhibitory self-control, which contribute to increased risky behaviors, including the initiation and progression of alcohol use. Compared to adults, adolescents are less susceptible to the negative effects of ethanol, but are more susceptible to the negative effects of stress, particularly social stress. Juvenile exposure to social isolation or binge ethanol disrupts synaptic connections, dendritic spine morphology, and myelin remodeling in the frontal cortex. These structural effects may underlie the behavioral and cognitive deficits seen later in life, including social and memory deficits, increased anxiety-like behavior and risk for alcohol use disorders (AUD). Although the alcohol and social stress fields are actively investigating the mechanisms through which these effects occur, significant gaps in our understanding exist, particularly in the intersection of the two fields. This review will highlight the areas of convergence and divergence in the fields of adolescent social stress and ethanol exposure. We will focus on how ethanol exposure or social isolation stress can impact the development of the frontal cortex and lead to lasting behavioral changes in adulthood. We call attention to the need for more mechanistic studies and the inclusion of the evaluation of sex differences in these molecular, structural, and behavioral responses.

Social reactivation of fear engrams enhances memory recall

Social interactions can bolster and protect memory performance. However, the relationship between social stimuli and individually learned memories remains enigmatic. Our work reveals that exposure to a stressed, naïve nonfamiliar conspecific or to the ambient olfactory–auditory cues of a recently stressed familiar conspecific induces reactivation of the cellular ensembles associated with a fear memory in the hippocampus. Artificially stimulating the hippocampal ensemble active during the social experience induces fearful behaviors in animals that have previously acquired a negative memory, revealing the interaction between individual history and social experience. The neural resurgence of fear-driving ensembles during social experiences leads to a context-specific enhancement of fear recall. Our findings provide evidence that unlike direct stressors, social stimuli reactivate and amplify an individual’s memories.

For group-living animals, the social environment provides salient experience that can weaken or strengthen aspects of cognition such as memory recall. Although the cellular substrates of individually acquired fear memories in the dentate gyrus (DG) and basolateral amygdala (BLA) have been well-studied and recent work has revealed circuit mechanisms underlying the encoding of social experience, the processes by which social experience interacts with an individual’s memories to alter recall remain unknown. Here we show that stressful social experiences enhance the recall of previously acquired fear memories in male but not female mice, and that social buffering of conspecifics’ distress blocks this enhancement. Activity-dependent tagging of cells in the DG during fear learning revealed that these ensembles were endogenously reactivated during the social experiences in males, even after extinction. These reactivated cells were shown to be functional components of engrams, as optogenetic stimulation of the cells active during the social experience in previously fear-conditioned and not naïve animals was sufficient to drive fear-related behaviors. Taken together, our findings suggest that social experiences can reactivate preexisting engrams to thereby strengthen discrete memories.

Cognitive Reserve in Model Systems for Mechanistic Discovery: The Importance of Longitudinal Studies

The goal of this review article is to provide a resource for longitudinal studies, using animal models, directed at understanding and modifying the relationship between cognition and brain structure and function throughout life. We propose that forthcoming longitudinal studies will build upon a wealth of knowledge gleaned from prior cross-sectional designs to identify early predictors of variability in cognitive function during aging, and characterize fundamental neurobiological mechanisms that underlie the vulnerability to, and the trajectory of, cognitive decline. Finally, we present examples of biological measures that may differentiate mechanisms of the cognitive reserve at the molecular, cellular, and network level.

Social vs. Nonsocial Housing Differentially Affects Perseverative Behavior in Rats (Ratus norvegicus)

Perseverance, also commonly referred to as grit or industriousness, is the continued effort exerted to complete goal-directed tasks. Many factors, such as stress, can contribute to perseverative behavior, but the role of sociality on perseverance in animal models has not been studied. In this experiment, perseverance was measured in Long-Evans rats; half of which were socially housed (SH) and the other half were nonsocially housed (NSH). Rats were placed in a continuous T-maze; one arm of the maze contained an unobstructed low value reward and the other arm contained a high value reward blocked by a barrier that progressively increased in height across testing sessions. We will hereon refer to the low value reward and high value reward as the low reward and the high reward, respectively. Perseverative behavior was assessed by time spent interacting with the barrier and trials were characterized as either adaptive perseverative trials (high reward obtainment) and maladaptive perseverative trials (low reward obtainment after abandoning attempts to overcome the high reward barrier). SH and NSH rats were equally proficient at overcoming a physical barrier to obtain a higher-valued reward, but the NSH rats spent more time interacting with the barriers during maladaptive perseverative trials than SH rats. NSH rats thus exhibited prolonged efforts to overcome the barrier only to ultimately travel to the low reward option. In contrast, SH rats selected the low reward option earlier in the trial and did not maladaptively perseverate without obtaining the high reward. Putative evidence for increased perseverance in NSH rats is explained in the context of maladaptive perseverative behavior rather than perseverance per se. Increased adaptability and acquisition of task-set in SH rats suggests a role of social housing in advantageous decision making.