Differences In Spatial Learning Research Articles

Effects of high-intensity chronic noise on spatial memory in male versus female rats.

The detrimental effects of high-intensity noise on the auditory system and emotional status, including the induction of anxiety, are well documented. Preclinical as well as epidemiological and clinical studies have solidly established differential responses between males and females to various stressful stimuli, including high-intensity white noise (HIWN). However, whether chronic exposure to noise affects cognitive functions and whether this effect is sex dependent has not been adequately addressed. In this study, we used two cognitive test paradigms, such as the Morris water maze (MWM) and the multi-branch maze (MBM), to test the effect of chronic HIWN on indices of spatial learning and memory in both male and female Wistar rats. Our findings indicate that daily (1 h) exposure to 100 dB of noise for 30 consecutive days induces different task-dependent responses in male versus female rats. For example, in the acquisition phase of MWM, female rats exposed to noise outperformed their male counterparts at twice the speed. Similarly, in the MBM test, noise-exposed female rats outperformed the male rats in reaching the nest box. It is clear from these studies that noise impairs cognitive functions twice as negatively in male rats as in female rats. Thus, sex-related differences in spatial learning and memory in response to HIWN must be taken into consideration when investigating the neurobiological components and/or treatment modalities.

Impacts of spatial learning on male prairie vole mating tactics in seminatural field enclosures are context dependent

Mating systems, and individual mating tactics therein, are regularly defined by patterns of space use and are inherent reflections of spatial cognition. Despite this, spatial learning is rarely considered in the context of mating tactics. The goal of this study was to determine the relationship between spatial learning and the mating tactics that males adopt. Specifically, we asked whether spatial learning predicts the adoption of a particular tactic, whether the adoption of a particular tactic results in differences in spatial learning and/or whether individual variance in spatial learning is flexible or persistent across time and mating tactic experiences. To this end, we assessed spatial learning of male prairie voles, Microtus ochrogaster , under laboratory conditions before and after allowing them to live freely in seminatural field enclosures. Male prairie voles adopt two types of mating tactics, each with distinct patterns of space use. Monogamous ‘resident’ males have relatively small home ranges and exhibit high degrees of territory overlap with one female (partner) and very little with others. Wanderer males, by contrast, have large territories that overlap with multiple females and remain single. Our data revealed that spatial learning might be more associated with wandering behaviour overall when comparing between tactics. However, we also found that the significance of space use and mating behaviour was contextually dependent, and that spatial learning impacted space use uniquely within each tactic. The relationship with pre-test spatial learning explained the variance for some patterns of space use in the field for residents, and the relationship with post-test spatial learning explained the variance for some patterns of space use in the field for wanderers. Taken together, we conclude that differences in spatial learning ability and how they relate to mating tactics are contextual and best interpreted by examining within- and between-tactic variation. • We tested spatial learning in the lab and alternative mating tactics in the field. • Spatial learning relates to individual variation in space use among mating tactics. • Good spatial learning predicted space use most characteristic of monogamous males. • Good spatial learning related to uncharacteristic space use for nonmonogamous males. • Spatial cognition contextualizes reproductive decision making in prairie voles.

Individual differences in spatial learning are correlated across tasks but not with stress response behaviour in guppies

Cognition is vital for carrying out behaviours required for survival and reproduction. Cognitive performance varies between species, but also between individuals within populations. While variation is a prerequisite for natural selection, selection does not act on traits in isolation. The extent to which cognitive traits covary with other aspects of phenotype (e.g. personality traits) may be important in shaping evolutionary dynamics. Here we adopted a multivariate approach to test spatial learning in male Poecilia reticulata and asked whether differences in cognitive performance are associated with (repeatable) differences in stress response behaviour. Functional links between cognitive traits and ‘stress coping style’ have been hypothesized. Furthermore, individual level studies of cognitive performance typically rely on multiple testing paradigms that may themselves be a stressor. There is a risk that variation in stress responsiveness is itself a cause of apparent, but artefactual variance in cognitive ability. Fish repeatedly experienced two spatial learning tasks (maze layouts) and an acute stress response test (open field trial). We found repeatable differences between individuals in performance within and across maze layouts. On average, performance improved with experience in the first maze, consistent with spatial learning, but not in the second. Individuals varied in the trajectory of mean performance with trial number in both mazes, suggesting they differ in ‘learning rate’. Acute stress response behaviour was repeatable but predicted neither average time to solve the maze nor learning rate. We found no support for between-individual correlation between acute stress response and cognitive performance. However, we highlight the possibility that cumulative, chronic stress effects may nevertheless cause declines in performance for some individuals (leading to lack of improvement in mean time to solve the second maze). If so, this may represent a pervasive but difficult challenge for our ability to robustly estimate learning rates in studies of animal cognition.

Sex Differences in Spatial Learning and Memory in Valproic Acid Rat Model of Autism: Possible Beneficial Role of Exercise Interventions.

In the current study, we first tried to determine sex differences in spatial learning and memory in the valproic acid (VPA) rat model of autism. Second, the effects of interval training (IT) and continuous training (CT) exercises were examined in male and female offsprings. To induce autism-like animal model, the pregnant rats were injected 500 mg/kg NaVPA (intraperitoneal) at the embryonic day 12.5. IT and CT aerobic exercises were started at postnatal day 56. Then, on postnatal days 84–89, a Morris water maze (MWM) test was conducted on the separate groups of offsprings. Aerobic training was performed on a rodent treadmill with 0% slope for 8 weeks, 5 days/week, and 50 min/day. Unlike control animals, VPA-exposed female offspring had a better performance than VPA-exposed male offspring in MWM acquisition. In the case of MWM reference memory, we did not observe a sex difference between VPA-exposed male and VPA-exposed female offspring. Both IT and CT exercises in both control and VPA-exposed male rats significantly improved MWM acquisition. Moreover, both IT and CT exercises significantly improved MWM acquisition in control female rats. In addition, IT exercise (but not CT) significantly improved MWM acquisition in VPA-exposed female offsprings. Both IT and CT exercises in VPA-exposed that male and female offsprings improved the MWM reference memory. In conclusion, our observation demonstrated that prenatal exposure to VPA affects the spatial learning and memory in a sex dependent manner. We have shown that both IT and CT exercises are able to improve cognitive function in healthy and autistic rat offsprings.

Sexual Dimorphism in the Effect of Neonatal Inflammatory Pain on Stress Reactivity of Hormonal Response and Cognitive Functions in Adult Rats.

The effect of moderate neonatal stress induced by inflammatory pain in rat pups of both sexes on the hormonal response and cognitive processes in adult animals was studied in the Morris water maze. No significant differences in spatial learning and memory were found in experimental rats exposed to neonatal inflammatory pain vs. control animals. However, experimental rats exhibited sex differences in long-term spatial memory whose efficiency was higher in males vs. females. After long-term memory testing, stress responsiveness of the hypothalamic-pituitary-adrenocortical axis, as assessed by the plasma corticosterone level in the formalin test, was higher in experimental males vs. females. Only experimental females exhibited differences between short-term and long-term memory, with the efficiency being higher in the former. Thus, sexual dimorphism was found in the effect of neonatal nociceptive stress on long-term spatial memory in adult rats: experimental males vs. females demonstrated more effective long-term memory combined with a higher stress reactivity of the hormonal response.

Novel measures of Morris water maze performance that use vector field maps to assess accuracy, uncertainty, and intention of navigational searches.

Most commonly used behavioral measures for testing learning and memory in the Morris water maze (MWM) involve comparisons of an animal's residence time in different quadrants of the pool. Such measures are limited in their ability to test different aspects of the animal's performance. Here, we describe novel measures of performance in the MWM that use vector fields to capture the motion of mice as well as their search pattern in the maze. Using these vector fields, we develop quantitative measures of performance that are intuitive and more sensitive than classical measures. First, we describe search patterns in terms of vector field properties and use these properties to define three metrics of spatial memory namely Spatial Accuracy, Uncertainty and, Intensity of Search. We demonstrate the usefulness of these measures using four different data sets including comparisons between different strains of mice, an analysis of two mouse models of Noonan syndrome (NS; Ptpn11 D61G and Ptpn11 N308D/+), and a study of goal reversal training. Importantly, besides highlighting novel aspects of performance in this widely used spatial task, our measures were able to uncover previously undetected differences, including in an animal model of NS, which we rescued with the mitogen activated protein kinase kinase (MEK) inhibitor SL327. Thus, our results show that our approach breaks down performance in the MWM into sensitive measurable independent components that highlight differences in spatial learning and memory in the MWM that were undetected by conventional measures.

Social dominance has limited effects on spatial cognition in a wild food-caching bird.

Social dominance has long been used as a model to investigate social stress. However, many studies using such comparisons have been performed in captive environments. These environments may produce unnaturally high antagonistic interactions, exaggerating the stress of social subordination and any associated adverse consequences. One such adverse effect concerns impaired cognitive ability, often thought to be associated with social subordination. Here, we tested whether social dominance rank is associated with differences in spatial learning and memory, and in reversal spatial learning (flexibility) abilities in wild food-caching mountain chickadees at different montane elevations. Higher dominance rank was associated with higher spatial cognitive flexibility in harsh environments at higher elevations, but not at lower, milder elevations. By contrast, there were no consistent differences in spatial learning and memory ability associated with dominance rank. Our results suggest that spatial learning and memory ability in specialized food-caching species is a stable trait resilient to social influences. Spatial cognitive flexibility, on the other hand, appears to be more sensitive to environmental influences, including social dominance. These findings contradict those from laboratory studies and suggest that it is critical to investigate the biological consequences of social dominance under natural conditions.

Sex differences in spatial learning and memory and hippocampal long-term potentiation at perforant pathway-dentate gyrus (PP-DG) synapses in Wistar rats

BackgroundRecent studies show that gender may have a significant impact on brain functions. However, the reports of sex effects on spatial ability and synaptic plasticity in rodents are divergent and controversial. Here spatial learning and memory was measured in male and female rats by using Morris water maze (MWM) task. Moreover, to assess sex difference in hippocampal synaptic plasticity we examined hippocampal long-term potentiation (LTP) at perforant pathway-dentate gyrus (PP-DG) synapses.ResultsIn MWM task, male rats outperformed female rats, as they had significantly shorter swim distance and escape latency to find the hidden platform during training days. During spatial reference memory test, female rats spent less time and traveled less distance in the target zone. Male rats also had larger LTP at PP-DG synapses, which was evident in the high magnitude of population spike (PS) potentiation and the field excitatory post synaptic potentials (fEPSP) slope.ConclusionsTaken together, our results suggest that sex differences in the LTP at PP-DG synapses, possibly contribute to the observed sex difference in spatial learning and memory.

In aged rats, differences in spatial learning and memory influence the response to late-life Environmental Enrichment

It has clearly been demonstrated that cognitive stimulation, physical exercise, and social engagement help counteract age-related cognitive decline. However, several important issues remain to be addressed. Given the wide differences in cognitive impairment found among individuals of the same age, identifying the subjects who will benefit most from late-life interventions is one such issue. Environmental Enrichment (EE) is a particularly valuable approach to do this. In this study, aged (21-month-old) rats were assigned to a better (BL) or a worse (WL) learner group (training phase) and to a non-impaired (NI) or an impaired (I) group (probe phase) by their performance on the Morris Water Maze, using the test performances of adult (12-month-old) rats as the cut-offs. The aged rats were retested after a 12-week EE or standard housing (SH) protocol. After 12weeks, the performances of SH rats had deteriorated, whereas all rats benefited from EE, albeit in different ways. In particular, the animals assigned to the BL and the NI groups prior to EE still performed as well as the adult rats (performance preservation) whereas, critically, the animals assigned to the WL and the I groups before EE showed such improved performances that they reached the level of the adult rats (performance improvement), despite having aged further. EE seems to induce the preservation in BLs and the improvement in WLs of spatial search strategies and the preservation in NIs and the increase in Is of a focused and protract research of the escape point. Our findings suggest that late-life EE prevents spatial learning and memory decline in still cognitively preserved animals and stimulates residual functional reserve in already cognitively compromised animals. Future research should focus on individually tailored stimulation protocols to improve their effect and afford a better understanding of the underlying processes.

A membrane protein insertion complex

The present study examined the long-standing concept that changes in hippocampal circuitry contribute to age-related learning impairment. Individual differences in spatial learning were documented in young and aged Long–Evans rats by using a hippocampal-dependent version of the Morris water maze. Postmortem analysis used a confocal laser-scanning microscopy method to quantify changes in immunofluorescence staining for the presynaptic vesicle glycoprotein, synaptophysin (SYN), in the principal relays of hippocampal circuitry. Comparisons based on chronological age alone failed to reveal a reliable difference in the intensity of SYN staining in any region that was examined. In contrast, aged subjects with spatial learning deficits displayed significant reductions in SYN immunoreactivity in CA3 lacunosum-moleculare (LM) relative to either young controls or age-matched rats with preserved learning. SYN intensity values for the latter groups were indistinguishable. In addition, individual differences in spatial learning capacity among the aged rats correlated with levels of SYN staining selectively in three regions: outer and middle portions of the dentate gyrus molecular layer and CA3-LM. The cross-sectional area of SYN labeling, by comparison, was not reliably affected in relation cognitive status. These findings are the first to demonstrate that a circuit-specific pattern of variability in the connectional organization of the hippocampus is coupled to individual differences in the cognitive outcome of normal aging. The regional specificity of these effects suggests that a decline in the fidelity of input to the hippocampus from the entorhinal cortex may play a critical role.

Exploring the effects of geographic scale on spatial learning

BackgroundInvestigating the relationship between the human body and its spatial environment is a critical component in understanding the process of acquiring spatial knowledge. However, few empirical evaluations have looked at how the visual accessibility of an environment affects spatial learning. To address this gap, this paper focuses on geographic scale, defined as the spatial extent visually accessible from a single viewpoint. We present two experiments in which we manipulated geographic scale using two perspectives, a ground level and an elevated view, in order to better understand the scale effect on spatial learning. Learning outcomes were measured using estimates of direction and self-reports of mental workload.ResultsIn contrast to our hypothesis, we found few differences in spatial learning when comparing different perspectives. However, our analysis of pointing errors shows a significant interaction effect between the scale and spatial ability: The elevated perspective reduced the differences in pointing errors between low and high spatial ability participants in contrast to when participants learned the environment at ground level alone. Bimodal pointing distributions indicate that participants made systematic errors, for example, forgetting turns or segments. Modeling these errors revealed a unified alternative representation of the environment and further suggests that low spatial ability participants benefited more from the elevated perspective in terms of spatial learning compared to high spatial ability participants.ConclusionsWe conclude that an increased geographic scale, which was accessible through an elevated perspective in this study, can help bridge the performance gap in spatial learning between low and high spatial ability participants.

Effect of age on discrimination learning, reversal learning, and cognitive bias in family dogs.

Several studies on age-related cognitive decline in dogs involve laboratory dogs and prolonged training. We developed two spatial tasks that required a single 1-h session. We tested 107 medium-large sized dogs: "young" (N=41, aged 2.5-6.5 years) and "old" (N=66, aged 8-14.5 years). Our results indicated that, in a discrimination learning task and in a reversal learning task, young dogs learned significantly faster than the old dogs, indicating that these two tasks could successfully be used to investigate differences in spatial learning between young and old dogs. We also provide two novel findings. First, in the reversal learning, the dogs trained based on the location of stimuli learned faster than the dogs trained based on stimulus characteristics. Most old dogs did not learn the task within our cut-off of 50 trials. Training based on an object's location is therefore more appropriate for reversal learning tasks. Second, the contrast between the response to the positive and negative stimuli was narrower in old dogs, compared to young dogs, during the reversal learning task, as well as the cognitive bias test. This measure favors comparability between tasks and between studies. Following the cognitive bias test, we could not find any indication of differences in the positive and negative expectations between young and old dogs. Taken together, these findings do not support the hypothesis that old dogs have more negative expectations than young dogs and the use of the cognitive bias test in older dogs requires further investigation.

Sex differences and the role of acute stress in the open-field tower maze

Many studies provide evidence that differences in spatial learning exist between males and females. However, it is necessary to consider non-mnemonic factors that may influence these findings. The present experiment investigated acquisition, retention, and the effects of stress on response- and place-learning in male and female rats. Rats were trained in an open-field tower maze. Procedures were used to minimize stress in the rats, and their ability to solve place- or response-learning in the maze was determined by analyzing a response variable (i.e., first choice correct response) that was not influenced by general locomotor activity. The results revealed that male and female rats acquire place- and response-learning at the same rate even though females moved significantly faster in the maze. However, females showed better retrieval of place-, but not response-learning compared to male rats. This effect appeared to be enhanced when the rats were tested immediately following an acute restraint stress. Furthermore, both female and male rats that were exposed to acute restraint stress showed less impairment than controls when subsequently tested in a novel situation. These findings have clinical implications that a mild physiological stress response can make one more cognitively resistant to adversities later in life.

Sex effects on spatial learning but not on spatial memory retrieval in healthy young adults

ObjectivesSex differences have been found in spatial learning and spatial memory, with several studies indicating that males outperform females. We tested in the virtual Morris Water Maze (vMWM) task, whether sex differences in spatial cognitive processes are attributable to differences in spatial learning or spatial memory retrieval in a large student sample. MethodsWe tested 90 healthy students (45 women and 45 men) with a mean age of 23.5 years (SD=3.5). Spatial learning and spatial memory retrieval were measured by using the vMWM task, during which participants had to search a virtual pool for a hidden platform, facilitated by visual cues surrounding the pool. Several learning trials assessed spatial learning, while a separate probe trial assessed spatial memory retrieval. ResultsWe found a significant sex effect during spatial learning, with males showing shorter latency and shorter path length, as compared to females (all p<0.001). Yet, there was no significant sex effect in spatial memory retrieval (p=0.615). Furthermore, post-hoc analyses revealed significant sex differences in spatial search strategies (p<0.05), but no difference in the number of platform crossings (p=0.375). ConclusionOur results indicate that in healthy young adults, males show faster spatial learning in a virtual environment, as compared to females. Interestingly, we found no significant sex differences during spatial memory retrieval. Our study raises the question, whether men and women use different learning strategies, which nevertheless result in equal performances of spatial memory retrieval.

Lewis and Fischer 344 rats as a model for genetic differences in spatial learning and memory: Cocaine effects

Lewis (LEW) and Fischer 344 (F344) rats are considered a model of genetic vulnerability to drug addiction. We previously showed important differences in spatial learning and memory between them, but in contrast with previous experiments demonstrating cocaine-induced enhanced learning in Morris water maze (MWM) highly demanding tasks, the eight-arm radial maze (RAM) performance was not modified either in LEW or F344 rats after chronic cocaine treatment. In the present work, chronically cocaine-treated LEW and F344 adult rats have been evaluated in learning and memory performance using the Y-maze, two RAM protocols that differ in difficulty, and a reversal protocol that tests cognitive flexibility. After one of the RAM protocols, we quantified dendritic spine density in hippocampal CA1 neurons and compared it to animals treated with cocaine but not submitted to RAM.LEW cocaine treated rats showed a better performance in the Y maze than their saline counterparts, an effect that was not evident in the F344 strain. F344 rats significantly took more time to learn the RAM task and made a greater number of errors than LEW animals in both protocols tested, whereas cocaine treatment induced deleterious effects in learning and memory in the highly difficult protocol. Moreover, hippocampal spine density was cocaine-modulated in LEW animals whereas no effects were found in F344 rats.We propose that differences in addictive-like behavior between LEW and F344 rats could be related to differences in hippocampal learning and memory processes that could be on the basis of individual vulnerability to cocaine addiction.

Gender differences in spatial learning, synaptic activity, and long-term potentiation in the hippocampus in rats: molecular mechanisms.

In tests of spatial ability, males outperform females both in rats and in humans. The mechanism underlying this gender differential learning ability and memory in spatial tasks remains unknown. Long-term potentiation (LTP) in the hippocampus is considered the basis for spatial learning and memory. The aims of this work were (a) to assess spatial learning and memory in male and female rats in the radial and Morris mazes; (b) to assess whether basal synaptic activity and LTP in the hippocampus are different in male and female rats; and (c) to identify the molecular mechanisms responsible for the gender differences in LTP. We analyzed in young male and female rats (a) performance in spatial tasks in the radial and Morris water mazes; (b) basal synaptic activity in hippocampal slices; and (c) LTP and some mechanisms modulating its magnitude. The results reported allow us to conclude that female rats show larger AMPA receptor-mediate synaptic responses under basal conditions, likely due to enhanced phosphorylation of GluR2 in Ser880 and increased amounts of GluR2-containing AMPA receptors in postsynaptic densities. In contrast, the magnitude of tetanus-induced LTP was lower in females than in males. This is due to reduced activation of soluble guanylate cyclase and the formation of cGMP, leading to lower activation of cGMP-dependent protein kinase and phosphorylation of GluR1 in Ser845, which results in lower insertion of AMPA receptors in the synaptic membrane and a lower magnitude of LTP. These mechanisms may contribute to the reduced performance of females in the radial and Morris water mazes.

Effects of chronic cocaine treatment during adolescence in Lewis and Fischer-344 rats: Novel location recognition impairment and changes in synaptic plasticity in adulthood

The use of Lewis (LEW) together with Fischer-344 (F344) rats has been proposed as an addiction model because of the addiction behavior differences of these two strains. We have previously suggested that these differences could be related to learning and memory processes and that they depend on the genetic background of these two strains of rats. Adolescence is a period of active synaptic remodeling, plasticity and particular vulnerability to the effects of environmental insults such as drugs of abuse. We have evaluated spatial memory using novel location recognition in LEW and F344 adult rats undergoing a chronic treatment with cocaine during adolescence or adulthood. In order to study whether synaptic plasticity mechanisms were involved in the possible changes in learning after chronic cocaine treatment, we carried out electrophysiological experiments in hippocampal slices from treated animals. Our results showed that, in LEW cocaine-treated rats, hippocampal memory was only significantly impaired when the drug was administered during adolescence whereas adult administration did not produce any detrimental effect in spatial memory measured in this protocol.Moreover, F344 rats showed clear difficulties carrying out the protocol even in standard conditions, confirming the spatial memory problems observed in previous reports and demonstrating the genetic differences in spatial learning and memory.Our experiments show that the effects in behavioral experiments are related to synaptic plasticity mechanisms. Long-term depression induced by the glutamate agonist NMDA (LTD-NMDA) is partially abolished in cocaine-treated animals in hippocampal slices from LEW rats. Hippocampal LTD-NMDA is partially inhibited in F344 animals regardless of whether saline or cocaine administration, suggesting the lack of plasticity of this strain that could be related to the inability of these animals to carry out the novel object location protocol.

Sex, but not Apolipoprotein E Polymorphism, Differences in Spatial Performance in Young Adults.

The purpose of this study was to examine how sex and apolipoprotein E (APOE) genotype contribute to individual differences in spatial learning and memory. The associations of APOE genotype with neurocognitive function have been well studied among the elderly but less is known at earlier ages. Young adults (n = 169, 88 females) completed three neurocognitive tasks: mental rotation, spatial span, and Memory Island, a spatial navigation test. Males outperformed females on all three tasks: finding the hidden targets more quickly on Memory Island (Cohen's d = 0.62) and obtaining higher scores on mental rotation (d = 0.54) and spatial span (d = 0.37). In contrast, no significant effects of APOE were observed. The identified sex differences elaborate upon past literature documenting sexually dimorphic performance on specific neurobehavioral tasks.

Sex differences in learning and memory following short-term dietary restriction in the rat

IntroductionAcute or prolonged dietary restriction has been shown to have significant effects on learning and memory, and also on the food seeking behaviour in animals. AimThis study investigated whether or not there are sex differences in spatial learning and memory following short-term dietary restriction in the rat. MethodsTwo month-old male (n=24) and female (n=24) Sprague-Dawley rats were randomly assigned to either (1) male or female control (i.e. normal diet regimen); (2) male or female 40% dietary restriction for either 2hours (2h-DR) or 2 weeks (2 wks-DR) duration. Following the restriction paradigm (i.e. either 2h or 2 weeks), animals were weighed, and learning and memory was assessed daily for a total of 5 days by Morris Water Maze. ResultsDietary restriction for 2h provoked high speed swimming in female rats compared to controls. However the females performance in water maze was inferior to the control animals. Two weeks after 40% DR resulted in reduction of male's body weight by 20% compared to their control group. However, both males and females showed difficulties in water maze learning and memory test after the 2 weeks 40% DR. The animals swam longer distance and took longer time to reach the platform when compared to their age-matched controls. ConclusionIn fully developed brain, adult animal's cognitive performance is shown to be affected by acute and prolonged stress in the form of food restriction. Interestingly, the impact of this stress was different according to the sex of the animals. In female rats, dietary restriction has a negative effect on learning and memory after 2h and 2 weeks intervals. In male rats, 2h of DR has a positive effect on learning and memory; however this effect is not maintained and by 2 weeks there is a negative effect similar to that seen in female animals.

Sex and boldness explain individual differences in spatial learning in a lizard

Understanding individual differences in cognitive performance is a major challenge to animal behaviour and cognition studies. We used the Eastern water skink (Eulamprus quoyii) to examine associations between exploration, boldness and individual variability in spatial learning, a dimension of lizard cognition with important bearing on fitness. We show that males perform better than females in a biologically relevant spatial learning task. This is the first evidence for sex differences in learning in a reptile, and we argue that it is probably owing to sex-specific selective pressures that may be widespread in lizards. Across the sexes, we found a clear association between boldness after a simulated predatory attack and the probability of learning the spatial task. In contrast to previous studies, we found a nonlinear association between boldness and learning: both 'bold' and 'shy' behavioural types were more successful learners than intermediate males. Our results do not fit with recent predictions suggesting that individual differences in learning may be linked with behavioural types via high-low-risk/reward trade-offs. We suggest the possibility that differences in spatial cognitive performance may arise in lizards as a consequence of the distinct environmental variability and complexity experienced by individuals as a result of their sex and social tactics.