Behavioural Brain Research

Recent literature points to a potential link between the evolution of complex social behavior and the posterior parietal cortex (PPC) in primates including humans (Parkinson & Wheatley, 2013). Thus far, this theory has been overlooked in other highly social animals that may have also evolved due to social selective pressures. In rodents, there is limited knowledge on the involvement of the PPC on sociality, and most studies of such behavior are limited to understanding social preference. We investigated the role of the PPC through two experiments using the 3-Chamber Sociability and Social Novelty test in rats (Crawley, 2004). In Experiment 1, we used a standard 3-Chamber paradigm, which included two novel demonstrators. In Experiment 2, this paradigm was altered to increase the difference in familiarity between demonstrators such that one demonstrator was highly familiar to the subject and the other was entirely novel. Rats with pre-testing permanent neurotoxic lesions were compared to sham surgery control rats, and the same rats were used for both experiments. Experiments 1 and 2 showed that both groups of rats preferred general social interaction, suggesting no deficit in sociability following PPC damage, regardless of demonstrator identity. Further, experimental and control rats showed similar levels of novelty preference following PPC damage, with novelty preferences increasing in Experiment 2. We argue that heightened novelty preference in Experiment 2 may reflect the increased difference in familiarity between demonstrators. Within the confines of the 3-Chamber task, our results suggest that PPC function was not required for general sociability or social novelty recognition. Because the PPC is implicated in abstract cognition, we argue that existing social tests in rodents may not adequately measure the complex cognitive capacities thought to be supported by the PPC. Future studies should investigate the role of the PPC in social cognition by employing behavioral tasks that require higher cognitive demand rather than testing inherent preference for social partners. Outside of our investigation of the PPC, these results show that social novelty preference can be manipulated through changes in familiarity of demonstrators, and that rats can discriminate others social identities.

Mild Traumatic Brain Injury (mTBI), or concussion, is the most common form of traumatic brain injury, which accounts for about 80% of cases. It is a common problem in contact sports and may lead to cognitive impairment. This study used the Wayne State University closed-head weight-drop model in lightly anesthetized and unrestrained Long Evans rats. This model allows for the rapid acceleration and deceleration of the head and torso, similar to the biomechanics in human mTBI. Rats were administered a single weight drop. Sham animals were treated the same as the mTBI group but were not subjected to weight drop. Rats were trained in an 8-arm radial maze to assess spatial working memory before and after weight drop manipulation. We observed that the injured rats spatial working memory performance significantly declined compared to the sham rats (cohens d = 1.88). Specifically, the performance of the sham group continued to improve after the sham procedure, whereas the performance of the injury group decreased. This study suggests the WDM model produces a deficit in spatial working memory in rats.

The platform-mediated active avoidance (PMA) task has been used as a rodent model of decision-based active avoidance in which rat learn to avoid a tone-signaled shock. Prior studies utilizing the PMA task have primarily investigated avoidance, freezing, and food-seeking behaviors, but few studies have thoroughly assessed darting behavior, a more recently identified measure of fear that has been largely explored in conditional fear paradigms. Here, we investigated the properties of darting that occur during the PMA task, in which rats either acquired the PMA task alone or with a social partner. We found that rats undergoing solitary PMA produced significantly more darting bouts, whereas rats undergoing social partner PMA produced darts that were faster and shorter in duration. We also found that darting in solitary PMA was predominantly concentrated at the platform, whereas darting in social partner PMA occurred more often outside of the platform and lever zones. Analysis of darting trajectories, which included movements surrounding each darting bout, revealed that darting was embedded in a broader movement strategy between the platform and lever zones, especially during solitary PMA, and this pattern increased across training days. These findings suggest that darting during the PMA task serves as a learned strategy to navigate between reward and safety and is modulated by social context, which is distinct from escape-like darting observed in auditory fear conditioning.

Autism is a common neurodevelopmental disorder that despite its complex etiology, is marked by deficits in prediction that manifest in a variety of domains including social interactions, communication, and movement. The tendency of individuals with autism to focus on predictable schedules and interests that contain patterns and rules highlights the likely involvement of the cerebellum in this disorder. One candidate-autism gene is contact in associated protein 2 (CNTNAP2), and variants in this gene are associated with sensory deficits and anatomical differences. It is unknown, however, whether this gene directly impacts the brains ability to make and evaluate predictions about future events. The current study was designed to answer this question by training a genetic knockout rat on a rapid speech sound discrimination task. Rats with Cntnap2 knockout (KO) and their littermate wildtype controls (WT) were trained on a validated rapid speech sound discrimination task that contained unpredictable and predictable targets. We found that although both genotype groups learned the task in both unpredictable and predictable conditions, the KO rats responded more often to distractors during training as well as to the target sound during the predictable testing conditions compared to the WT group. There were only minor effects of sex on performance and only in the unpredictable condition. The current results provide preliminary evidence that removal of this candidate-autism gene may interfere with the learning of unpredictable scenarios and enhance reliance on predictability. Future research is needed to probe the neural anatomy and function that drives this effect.

Cerebellar communication with the prefrontal cortex (PFC) may play a significant role in cognitive functions. Our previous studies found that rule-based (RB) category learning depends on the PFC in humans and rats. The PFC is also crucial for behavioral flexibility following rule-changes in various tasks. Very little is known regarding the role of the cerebellum in RB category learning. The current study was designed to determine whether the cerebellum plays a role in RB category learning, and in categorization following a rule switch. Female and male rats were given bilateral lesions of the lateral cerebellar nuclei (LCN) or a control surgery and trained on an RB category learning task followed by a category rule switch. A subset of rats was trained on a control discrimination task with the same trial procedures as the categorization task. Rats with LCN lesions took significantly longer to learn both the first and second category rules but were not impaired on the control task. Computational modeling revealed less task engagement and increased switching between engaged and non-engaged states in the LCN lesion group. Several measures of task performance indicated that the category learning deficit was not caused by a motor impairment, response bias, or an inability to discriminate the stimuli. The category learning deficits with LCN lesions were related to reduced accuracy of stimulus classification, an inability to maintain task engagement, and loss of flexibility. The results show, for the first time, that the cerebellum plays a crucial role in category learning and category rule-switching.

House mice adjust their signaling behavior depending on the social context of an interaction, but which aspects of context elicit the strongest responses from these individuals is often difficult to determine. To explore how internal and external contextual factors influence how of house mice produce and respond to social signals, we assessed how dominant and subordinate male mice differed in their ultrasonic vocalization (USV) production in response to playback of broadband vocalizations (BBVs, or squeaks) when given limited access to a stimulus female. We used a repeated measures design in which each male was exposed to two types of trials with different odor conditions: either just female odors (Fem condition) or female odors in addition to the odors of potential competitors, other males (Fem+Male condition). The presence of odors from other males in this assay served as a proxy for an "audience" as the male interacted with the stimulus female. These conditions were replicated for two distinct cohorts of individuals: males exposed to the odor of familiar competitors in the Fem+Male condition (Familiar odor cohort), and males exposed to the odor of unfamiliar competitors in the Fem+Male condition (Unfamiliar odor cohort). By assessing dominance status of the focal individual and familiarity of the "audience", we are able to explore how these factors may affect one another as males respond to BBVs. Dominants and subordinates did not differ in their baseline vocal production (vocalizations produced prior to squeak playback) or response to squeaks. However, all groups, regardless of dominance status or odor condition, reduced their vocal production in response to BBV playback. The presence of unfamiliar male odor prompted mice to decrease their baseline level of calling and decrease the complexity of their vocal repertoire compared to trials that only included female odor, and this effect also did not differ across dominance status. Importantly, the presence of male odor did not affect vocal behavior when the male odor was familiar to the focal individual. These findings suggest that mice alter their vocal behavior during courtship interactions in response to cues that indicate the presence of potential competitors, and this response is modulated by the familiarity of these competitor cues.

Humans show distinct social behaviours when we recognise social similarity in opponents that are members of the same social group. However, little attention has been paid to the role of social similarity in non-human animals. In Wistar subject rats, the presence of an unfamiliar Wistar rat mitigated stress responses, suggesting the importance of social similarity in this phenomenon. We found that the presence of unfamiliar Sprague-Dawley (SD) or Long-Evans (LE) rats, but not an unfamiliar Fischer 344 (F344) rat, similarly mitigated stress in subject rats. It is therefore possible that the subject rats recognised social similarity to unfamiliar SD and LE rats. In this study, we demonstrated that Wistar subject rats were capable of categorizing unfamiliar rats based on their strain, and that Wistar subjects showed a preference for unfamiliar Wistar, SD, and LE rats over F344 rats. However, the subject rats did not show a preference among Wistar, SD, and LE rats. In addition, the results were not due to an aversion to F344 rats, and preference was not affected when anaesthetised rats were presented to subject rats. The findings suggested that rats recognise social similarity to certain unfamiliar strains of rats.

Chemotherapy-induced cognitive impairment (CICI) affects up to 75% of cancer survivors between 6-months and 20-years post-treatment. Impairments include memory loss, learning difficulties, inability to concentrate and a decrease in processing speed, all of which can negatively impact quality of life. Several mechanisms are proposed to drive these impairments, with evidence implicating neuroinflammation as a key contributor. However, the time course over which impairments occur is less well-established. Several preclinical studies have focused on acute (0-7 days) and sub-acute (8-days to 12-weeks) time-points following chemotherapy, but few have investigated more longer-term time-points. This study therefore aimed to understand the evolution of cognitive changes following methotrexate (MTX) or 5-flurouracil (5-FU) chemotherapy treatment, assessing three time-points: acute (96-hour), sub-acute (31-days) and chronic (93-days). Further, we investigated whether alterations in cognition were associated with concomitant changes in neuroinflammation, assessed via astrocytic reactivity. Female Sprague Dawley rats received two intraperitoneal injections of MTX, 5-FU or saline and were assessed on the novel object recognition, 5-choice serial reaction time task and Barnes maze. Hippocampal (HIPP) and pre-frontal cortex (PFC) tissue was examined for GFAP expression. Results indicate that both MTX and 5-FU exposure were associated with impairments in spatial memory, task acquisition, and processing speed at 31-days, with impairment ameliorated by 93-days post-treatment. While MTX and 5-FU increased GFAP expression across all time-points, with the largest changes at 96-hours and 31-days, drug-specific and region-specific variations were noted. These results provide valuable insight into the complexity of the neuroinflammatory response in CICI. While neuroinflammation may be a promising therapeutic target, further work is required to fully understand this response, including which aspects to target and at what time-points, to ensure optimal outcomes for cancer patients treated with chemotherapy.

Vocal communication depends not only on the acoustic features and rate of vocalizations, but also on their timing relative to the vocalizations of others. In this study, we examined whether ultrasonic vocalizations (USVs) produced by adult female Mongolian gerbils during freely moving social interactions are temporally related to the vocal timing of a partner. Using USVCAM, we assigned each USV to an individual caller and evaluated whether brief USVs exhibit turn-taking-like temporal organization by analyzing response latency after partner calls, call overlap rate, and circular-shift surrogate data. The offset-to-onset gaps of alternating vocalizations were concentrated within a short time range, with a median of 130 ms. In addition, the call overlap rate was significantly lower in the observed data than in the circularly shifted surrogate data, indicating that USVs occurred with short latencies after partner calls while being less likely to overlap with ongoing partner calls. Furthermore, USV counts were reduced in unoperated Ctrl animals that interacted with devocalized Mute animals. These findings suggest that gerbil USVs may be coordinated in relation to partner vocal timing and vocal input. This study provides a basis for understanding rodent USVs not merely as individual vocal outputs, but as temporally organized dyadic social signals.

Understanding the neural basis of fear expression in rodents has implications for understanding pathological fear responses that characterize posttraumatic stress disorder. Even though posttraumatic stress disorder is more common in females, little is known about the neural circuit interactions supporting fear expression in female rodents. In this study, we were interested in determining whether neural activity associated with the expression of contextual fear differed between males and females within the projections from the medial prefrontal cortex to the ventrolateral periaqueductal gray, and in the medial prefrontal cortex in neurons that do not project to the periaqueductal gray. We infused a viral retrograde tracer into the ventrolateral periaqueductal gray in male and female rats and trained them in a contextual fear conditioning task. The following day rats were re-exposed to the conditioning context and were sacrificed shortly thereafter. Neural activity was measured using EGR1 immunofluorescence. The behavioral results showed that males exhibited higher levels of freezing during the context test than females. Male rats that underwent training and testing showed an increase in the proportion of viral infected cells that express EGR1 in the PL compared to rats that had only received context exposure. Trained female rats were not different than controls, however a direct comparison between sexes was not different. In cells not labeled by the tracer, males showed higher levels of fear-induced EGR1 expression in the prelimbic cortex than females. Conversely, females showed higher levels of EGR1 expression in the infralimbic cortex following testing as compared to males. These results suggest that sex differences in the expression of contextual fear may involve differences in the relative activity levels of the prelimbic and infralimbic cortex.

Recent studies have highlighted the crucial role of microglia in fear learning and memory. This supports the potential therapeutic value of the anti-inflammatory agent minocycline, which regulates microglial activity, in psychiatric disorders involving dysregulated emotional memory. To assess the impact of minocycline during a tractable intervention window, we examined its acute systemic effects on the reconsolidation, extinction, and forgetting of contextual fear memory (CFM) in rats. Our findings show that the effects of minocycline on fear memory and anxiety-like behaviours depend on sex, memory activation (i.e., whether it was retrieved), and memory age. In males with recently acquired CFM, minocycline given before retrieval enhanced extinction and reduced fear expression. When administered without retrieval, it disrupted passive forgetting, increasing evoked fear behaviour. This extinction-enhancing effect did not occur with older (28-day) memories rather it strengthened CFM through enhancing reconsolidation. In contrast, in females, minocycline increased the expression of recent fear memories regardless of retrieval, without affecting extinction or forgetting. This elevated fear expression appeared linked to heightened anxiety-like behaviour. These findings suggest that minocycline, or other microglia-targeting agents, would need to be used in a highly selective and targeted manner to therapeutically modulate pathological fear memories. Minocycline may be beneficial as an adjunct to exposure therapy in men explicitly retrieving recent fear or trauma-related memories, but outside these conditions, it may worsen fear expression. These results help explain the mixed findings from therapeutic trials using minocycline in psychiatry and support the application of a more precision approach in any future applications.

The relationships between distinct abilities and their interdependencies during memory tasks and motor learning activities are not clear. An important question is whether being proficient in memory or motor learning tasks also translates into better performance in another, similar task - reflecting potential generalization of motor learning abilities. To investigate the correlation between memory performance and motor learning, we used a combination of behavioral tasks that assess general exploratory behavior, declarative memory, and fine motor learning in female mice. For the exploratory behavior, we used the Open Field task, and assessed declarative memory using the Novel Object Recognition and Y-maze. Motor learning was assessed through the Vertical Pole and Pellet Reaching task. We found a negative correlation between the Vertical Pole task and the motor learning task, where a shorter time for an individual to turn on a pole correlated with an increased number of attempts to reach a sugar pellet in the motor learning task. Additionally, a positive correlation was found between the Y-maze and the motor learning task, where a higher exploration rate indicated a higher success ratio in the pellet reaching task. These results can be used to conduct a pre-study for challenging motor tasks that include pre-behavioral procedures on mice. Our study indicates that both the Vertical Pole and the Y-maze can be suitable predictors of motor learning performance and activity.

The "two-system" framework of fear proposed by LeDoux and Pine (2016) sparked a discussion on the understanding of fear, prompting a reevaluation of rodent fear conditioning studies. We propose that 22kHz ultrasonic vocalizations (USV) may symbolize the subjective negative emotional states in rats. To evaluate this, we designed a series of fear conditioning experiments with varied parameters, comparing the expression of 22kHz USV and body freezing - a traditional fear index. These expressions were further assessed in fear generalization tests. Our findings suggest a distinct separation between body freezing and 22kHz vocalizations in fear conditioning under different conditions. The results indicate that 22kHz USV may more accurately signify the subjective state of fear, whereas body freezing may denote an automatic defensive response in rats. Consequently, we posit that the two-system fear framework may extend to rodent fear conditioning paradigms. Therefore, researchers should place greater emphasis on 22kHz vocalizations when investigating the subjective state of fear.

Mice use their whiskers to convey sensory information, navigate, and explore their environment. We investigated the behavioral impact of the disruption of somatotopic patterning along the whisker-to-barrel pathway utilizing two mouse models: Barrelless (BRL) mice, an adenylyl cyclase 1 variation, in which somatotopic patterning is absent in the barrel cortex, and Prrxl1-/- mice, a genetic knockout in which patterning is disrupted along the entire lemniscal pathway. A textured novel object recognition test was conducted to investigate whisker-dependent discriminatory behavior, and an open field test was conducted to investigate exploratory behavior. Results were compared to an outbred strain (CD-1) and demonstrated that BRL mice were able to discriminate, whereas Prrxl1-/- mice were unable to discriminate between textures, and that both strains exhibited increased anxiety. Exploratory and locomotor behavior increased in BRL mice but decreased in Prrxl1-/- mice. Together, the results suggest that somatotopy may be related to behavioral phenotype.

Attention deficits emerge early in Alzheimers disease (AD), where cholinergic dysfunction compromises goal-directed behavior and cognitive control. Therefore, attentional impairments may serve as early indicators of cognitive decline, and also as meaningful targets for therapeutic intervention. Despite their clinical importance, attention deficits remain under- targeted by current treatments, which offer only modest benefit. To support development of more effective therapies, preclinical models that closely mirror human neurobiology and behavior are essential. Non-human primates (NHPs), with their high degree of cortical and functional similarity to humans, particularly in prefrontal regions, offer a uniquely translational platform for evaluating cognitive enhancers. We assessed pharmacological interventions targeting sustained attention using the Continuous Performance Test (CPT) in adult male cynomolgus macaques. Monkeys were trained to detect target stimuli while ignoring distractors, achieving individualized stable performance. To simulate cholinergic dysfunction, we administered scopolamine, a muscarinic acetylcholine receptor antagonist, which produced dose-dependent declines in accuracy and reaction time. Mild and severe impairment levels were identified within each animal. We then tested three compounds: nicotine, guanfacine, and donepezil. Nicotine, a nicotinic receptor agonist, fully restored performance across both impairment levels, suggesting potential benefit in both early and advanced AD. Guanfacine, an 2A adrenergic agonist, improved accuracy only under mild impairment, while donepezil, an acetylcholinesterase inhibitor, showed inconsistent effects. None of the compounds reversed scopolamine-induced slowing of reaction time, indicating specificity for attentional control. These findings highlight the utility of the NHP CPT as a pharmacologically sensitive model for detecting attentional dysfunction and evaluating pro-cognitive therapeutics in aging and neurodegeneration.

Traumatic brain injuries (TBIs) result from impact to or rapid displacement of the brain and can lead to various neurological deficits involving working memory, decision-making, and anxiety. While large-scale effects of brain damage are well-described for more severe TBIs, less is known about the extent and duration of cognitive deficits at the mild level. Interval timing can provide a helpful window into cognition in mice and humans. Interval-timing behavior is impaired in a wide range of neuropsychiatric disease states, such as Parkinsons disease. Furthermore, novel object recognition (NOR) and the Barnes maze (BM) tests are valuable assays for evaluating spatial learning, working memory, and anxiety-like behavior in mice. Here, we employed a weight-drop model of mild TBI (mTBI) to investigate changes in internal cognitive states resulting from mTBI treatment. mTBI mice were not significantly impaired in either interval timing or NOR, but they demonstrated impaired spatial memory in the Barnes Maze. Interestingly, within-sex comparisons revealed impairments in male mTBI mice in the interval-timing task and the NOR, suggesting that male and female mice may be differently affected by mTBIs.

The ability to learn by observing the behavior of others is both energy efficient and brings high survival value, making it an important learning tool for many species in the animal kingdom. As such, several forms of observational learning have been documented in a myriad of species. In the laboratory, rodents have proven useful models for studying different forms of observational learning, however, the most robust learning paradigms typically rely on aversive stimuli, like foot shocks, to drive the social acquisition of fear. Non-fear-based tasks have also been developed, but these rarely succeed in having observer animals perform a new behavior de novo. Consequently, much less is known regarding the cellular mechanisms supporting non-fear-based types of learning, such as visuomotor skill acquisition. To address this we developed a reward-based social learning paradigm in adult rats, in which observer animals learn to tap lit spheres in a specific sequence by watching skilled demonstrators, with successful trials leading to rewarding intracranial stimulation in both observers and performers. Following three days of observation and a 24-hour delay, observer animals outperformed control animals on several metrics of task performance and efficiency, with a subset of observers demonstrating correct performance immediately when tested. This paradigm thus introduces a novel tool to investigate the neural circuits supporting observational learning and memory for visuomotor behavior, a phenomenon about which little is understood, particularly in rodents.

Mild traumatic brain injury (mTBI) is the most common type of traumatic brain injury. Symptoms following mTBI fall into physical, emotional, sleep, and cognitive categories, with memory deficits being a commonly documented sequelae. Whereas many animal models of mTBI exist, relatively few studies have examined the cognitive deficits of mTBI with human-like cognitive tasks. The Wayne State University Closed Head Weight Drop Model recapitulates critical physical elements of sport-related concussions and trauma-based mTBI. However, until now, this model has not previously been evaluated using a human-like memory task. Rats were trained in an odor-based item-in-context task that dissociates episodic and non-episodic memory (Panoz-Brown et al., Current Biology, 2016). The animals then underwent either a weight drop or a sham procedure. After the manipulation, animals were assessed in the item-in-context task. Episodic memory was significantly impaired in the injured rats by over 10% but not in the sham rats. Non-episodic memory was not impaired in either group. Additionally, a time-course immunohistochemical analysis of the hippocampus was performed to examine possible time-dependent changes in ionized calcium-binding adaptor molecule 1 (iba1), a marker of activated microglia/macrophages and glial fibrillary acidic protein (GFAP), a marker of astrocytes. Concussion injury was associated with time-dependent morphological changes in astrocytes and microglia in injured rats compared to sham rats. This study is the first to document episodic memory impairment in an animal model of mTBI.

Rationale: Nearly one third of women of reproductive age in the United States are prescribed opioids annually; 14% will fill an opioid prescription during pregnancy, and one in five report misuse. Opioid use during pregnancy has given rise to an increasing population of infants born with gestational opioid exposure. At school age, these children show neurodevelopmental impairment and higher rates of learning disability. Objectives: To characterize how exposure to exogenous opioids during brain development affects learning and memory performance, our lab has developed a rat model of perigestational opioid exposure that closely recapitulates a clinically relevant dosing timeline by beginning morphine exposure before pregnancy and continuing through the first postnatal week. Male and female offspring generated from this model were assessed on several facets of learning and memory during adolescence. Results: Here, we report that morphine exposure selectively impaired spatial learning, as measured by the Barnes Maze, and associative learning, as measured by an Attentional Set Shift Task, without significantly impacting working or short-term memory. Environmental enrichment rescued the spatial learning deficit in males but not females. Conclusion: Our findings suggest that gestational opioid exposure can impair performance in complex cognitive tasks that are attenuated by non-invasive, non-pharmacological intervention.

The rostral anterior cingulate cortex (rACC) is a critical brain structure related to defensive behavior. However, still unclear is whether the rACC also plays a role in defensive behavior induced by electrical stimulation of the dorsal periaqueductal gray (dPAG). In the present study, rats were implanted with electrodes into the dPAG to determine freezing and escape response thresholds after sham or bilateral electrolytic lesions of the rACC. The duration of freezing behavior that outlasted electrical stimulation of the dPAG was also measured. The next day, these animals were subjected to contextual fear conditioning using footshock as an unconditioned stimulus. Lesions of the rACC did not change aversive freezing and escape response thresholds but disrupted post-dPAG stimulation freezing. The lesions also disrupted defensive freezing behavior and analgesia in the formalin test in response to contextual cues previously associated with footshock. These results indicate that the rACC is involved in some but not all aspects of defensive behavior generated at the level of the dPAG. The rACC also appears to play an important role in contextual fear conditioning.