The causes of variation in learning and behavior: why individual differences matter

A vast space of compact strategies for effective decisions

Inference-based decision-making, which underlies a broad range of behavioral tasks, is typically studied using a small number of handcrafted models. We instead enumerate a complete ensemble of strategies that could be used to effectively, but not necessarily optimally, solve a dynamic foraging task. Each strategy is expressed as a behavioral "program" that uses a limited number of internal states to specify actions conditioned on past observations. We show that the ensemble of strategies is enormous-comprising a quarter million programs with up to five internal states-but can nevertheless be understood in terms of algorithmic "mutations" that alter the structure of individual programs. We devise embedding algorithms that reveal how mutations away from a Bayesian-like strategy can diversify behavior while preserving performance, and we construct a compositional description to link low-dimensional changes in algorithmic structure with high-dimensional changes in behavior. Together, this work provides an alternative approach for understanding individual variability in behavior across animals and tasks.

Measuring the replicability of our own research

In the study of transgenic mouse models of neurodevelopmental and neurodegenerative disorders, we use batteries of tests to measure deficits in behaviour and from the results of these tests, we make inferences about the mental states of the mice that we interpret as deficits in "learning", "memory", "anxiety", "depression", etc. This paper discusses the problems of determining whether a particular transgenic mouse is a valid mouse model of disease X, the problem of background strains, and the question of whether our behavioural tests are measuring what we say they are. The problem of the reliability of results is then discussed: are they replicable between labs and can we replicate our results in our own lab? This involves the study of intra- and inter- experimenter reliability. The variables that influence replicability and the importance of conducting a complete behavioural phenotype: sensory, motor, cognitive and social emotional behaviour are discussed. Then the thorny question of failure to replicate is examined: Is it a curse or a blessing? Finally, the role of failure in research and what it tells us about our research paradigms is examined.

The Misguided Veneration of Averageness in Clinical Neuroscience: A Call to Value Diversity over Typicality

Research and practice in clinical neurosciences often involve cognitive assessment. However, this has traditionally used a nomothetic approach, comparing the performance of patients to normative samples. This method of defining abnormality places the average test performance of neurologically healthy individuals at its center. However, evidence suggests that neurological 'abnormalities' are very common, as is the diversity of cognitive abilities. The veneration of central tendency in cognitive assessment, i.e., equating typicality with healthy or ideal, is, I argue, misguided on neurodiversity, bio-evolutionary, and cognitive neuroscientific grounds. Furthermore, the use of average performance as an anchor point for normal performance is unreliable in practice and frequently leads to the mischaracterization of cognitive impairments. Examples are explored of how individuals who are already vulnerable for socioeconomic reasons can easily be over-pathologized. At a practical level, by valuing diversity rather than typicality, cognitive assessments can become more idiographic and focused on change at the level of the individual. The use of existing methods that approach cognitive assessment ideographically is briefly discussed, including premorbid estimation methods and informant reports. Moving the focus away from averageness to valuing diversity for both clinical cognitive assessments and inclusion of diverse groups in research is, I argue, a more just and effective way forward for clinical neurosciences.

Cognitive Test Solution in Mice with Different Brain Weights after Atomoxetine

In this paper, the data are presented concerning different reactions to seven daily injections of atomoxetine in two mouse strains differing in relative brain weight. Atomoxetine affected the performance in a puzzle-box cognitive test in a complicated way-the large brain mice were less successful at task solutions (presumably because they were not afraid of the brightly lit test box), while the small brain strain of atomoxetine treated mice solved the task more successfully. The behavior of all atomoxetine treated animals was more active in an aversive situation (an unescapable slippery funnel, (analogous to the Porsolt test) and the time of immobility decreased significantly in all atomoxetine treated mice. The general patterns of behavioral reactions to atomoxetine in the cognitive test and other interstrain differences demonstrated in these experiments made it possible to suggest that differences in ascending noradrenergic projections between the two strains used exist. Further analysis of the noradrenergic system in these strains is needed (and further analysis of the effects of drugs which affect noradrenergic receptors).

Two-stage reinforcement learning task predicts psychological traits

External sources of information influence human actions. However, psychological traits (PTs), considered internal variables, also play a crucial role in decision making. PTs are stable across time and contexts and define the set of behavioral repertoires that individuals express. Here, we explored how multiple metrics of adaptive behavior under uncertainty related to several PTs. Participants solved a reversal-learning task with volatile contingencies, from which we characterized a detailed behavioral profile based on their response sequences. We then tested the relationship between this multimetric behavioral profile and scores obtained from self-report psychological questionnaires. The PT measurements were based on the Hierarchical Taxonomy Of Psychopathology (HiTOP) model. By using multiple linear regression models (MLRMs), we found that the learning curves predicted important differences in the PTs and task response times. We confirmed the significance of these relationships by using random permutations of the predictors of the MLRM. Therefore, the behavioral profile configurations predicted the PTs and served as a "fingerprint" to identify participants with a high certainty level. We discuss briefly how this characterization and approach could contribute to better nosological classifications.

Comparable performance on a spatial memory task in data collected in the lab and online

Online data collection offers a wide range of benefits including access to larger and more diverse populations, together with a reduction in the experiment cycle. Here we compare performance in a spatial memory task, in which participants had to estimate object locations following viewpoint shifts, using data from a controlled lab-based setting and from an unsupervised online sample. We found that the data collected in a conventional laboratory setting and those collected online produced very similar results, although the online data was more variable with standard errors being about 10% larger than those of the data collected in the lab. Overall, our findings suggest that spatial memory studies using static images can be successfully carried out online with unsupervised samples. However, given the higher variability of the online data, it is recommended that the online sample size is increased to achieve similar standard errors to those obtained in the lab. For the current study and data processing procedures, this would require an online sample 25% larger than the lab sample.

Heterogeneity of performances in several inhibitory control tasks: male rhesus macaques are more easily distracted than females

Inhibitory control, the ability to override a dominant response, is crucial in many aspects of everyday life. In animal studies, striking individual variations are often largely ignored and their causes rarely considered. Hence, our aims were to systematically investigate individual variability in inhibitory control, to replicate the most common causes of individual variation (age, sex and rank) and to determine if these factors had a consistent effect on three main components of inhibitory control (inhibition of a distraction, inhibition of an action, inhibition of a cognitive set). We tested 21 rhesus macaques (Macaca mulatta) in a battery of validated touchscreen tasks. We first found individual variations in all inhibitory control performances. We then demonstrated that males had poorer performances to inhibit a distraction and that middle-aged individuals exhibited poorer performance in the inhibition of a cognitive set. Hence, the factors of age and sex were not consistently associated with the main components of inhibitory control, suggesting a multi-faceted structure. The rank of the subjects did not influence any inhibitory control performances. This study adopts a novel approach for animal behaviour studies and gives new insight into the individual variability of inhibitory control which is crucial to understand its evolutionary underpinnings.

Are the symptoms really remitting? How the subjective interpretation of outcomes can produce an illusion of causality

Judgments of a treatment’s effectiveness are usually biased by the probability with which the outcome (e.g., symptom relief) appears: even when the treatment is completely ineffective (i.e., there is a null contingency between cause and outcome), judgments tend to be higher when outcomes appear with high probability. In this research, we present ambiguous stimuli, expecting to find individual differences in the tendency to interpret them as outcomes. In Experiment 1, judgments of effectiveness of a completely ineffective treatment increased with the spontaneous tendency of participants to interpret ambiguous stimuli as outcome occurrences (i.e., healings). In Experiment 2, this interpretation bias was affected by the overall treatment-outcome contingency, suggesting that the tendency to interpret ambiguous stimuli as outcomes is learned and context-dependent. In conclusion, we show that, to understand how judgments of effectiveness are affected by outcome probability, we need to also take into account the variable tendency of people to interpret ambiguous information as outcome occurrences.

Differential associations of neurobehavioral traits and cognitive ability to academic achievement in higher education

BACKGROUND

People vary between each other on several neurobehavioral traits, which may have implications for understanding academic achievement.

METHODS

University-level Psychology or Engineering students were assessed for neurobehavioral traits, intelligence, and current psychological distress. Scores were compared with their grade point average (GPA) data.

RESULTS

Factors associated with higher GPA differed markedly between groups. For Engineers, intelligence, but not neurobehavioral traits or psychological distress, was a strong correlate of grades. For Psychologists, grades were not correlated with intelligence but they were with the neurobehavioral traits of executive dysfunction, disinhibition, apathy, and positive schizotypy. However, only the latter two were associated independently of psychological distress. Additionally, higher mixed-handedness was associated with higher GPA in the combined sample.

CONCLUSIONS

Neurological factors (i.e., neurobehavioral traits and intelligence), are differentially associated with university-level grades, depending on the major studied. However, mixed-handedness may prove to be a better general predictor of academic performance across disciplines.

The redundancy effect is related to a lack of conditioned inhibition: Evidence from a task in which excitation and inhibition are symmetrical

Rescorla and Wagner’s model of learning describes excitation and inhibition as symmetrical opposites. However, tasks used in human causal learning experiments, such as the allergist task, generally involve learning about cues leading to the presence or absence of the outcome, which may not reflect this assumption. This is important when considering learning effects which provide a challenge to this model, such as the redundancy effect. The redundancy effect describes higher causal ratings for the blocked cue X than for the uncorrelated cue Y in the design A+/AX+/BY+/CY–, the opposite pattern to that predicted by the Rescorla–Wagner model, which predicts higher associative strength for Y than for X. Crucially, this prediction depends on cue C gaining some inhibitory associative strength. In this article, we used a task in which cues could have independent inhibitory effects on the outcome, to investigate whether a lack of inhibition was related to the redundancy effect. In Experiment 1, inhibition for C was not detected in the allergist task, supporting this possibility. Three further experiments using the alternative task showed that a lack of inhibition was related to the redundancy effect: the redundancy effect was smaller when C was rated as inhibitory. Individual variation in the strength of inhibition for C also determined the size of the redundancy effect. Given that weak inhibition was detected in the alternative scenario but not in the allergist task, we recommend carefully choosing the type of task used to investigate associative learning phenomena, as it may influence results.

The impact of environmental interventions among mouse siblings on the heritability and malleability of general cognitive ability

General cognitive ability can be highly heritable in some species, but at the same time, is very malleable. This apparent paradox could potentially be explained by gene-environment interactions and correlations that remain hidden due to experimental limitations on human research and blind spots in animal research. Here, we shed light on this issue by combining the design of a sibling study with an environmental intervention administered to laboratory mice. The analysis included 58 litters of four full-sibling genetically heterogeneous CD-1 male mice, for a total of 232 mice. We separated the mice into two subsets of siblings: a control group (maintained in standard laboratory conditions) and an environmental-enrichment group (which had access to continuous physical exercise and daily exposure to novel environments). We found that general cognitive ability in mice has substantial heritability (24% for all mice) and is also malleable. The mice that experienced the enriched environment had a mean intelligence score that was 0.44 standard deviations higher than their siblings in the control group (equivalent to gains of 6.6 IQ points in humans). We also found that the estimate of heritability changed between groups (55% in the control group compared with non-significant 15% in the enrichment group), analogous to findings in humans across socio-economic status. Unexpectedly, no evidence of gene-environment interaction was detected, and so the change in heritability might be best explained by higher environmental variance in the enrichment group. Our findings, as well as the 'sibling intervention procedure' for mice, may be valuable to future research on the heritability, mechanisms and evolution of cognition.This article is part of the theme issue 'Causes and consequences of individual differences in cognitive abilities'.

Interpreting and Utilising Intersubject Variability in Brain Function

We consider between-subject variance in brain function as data rather than noise. We describe variability as a natural output of a noisy plastic system (the brain) where each subject embodies a particular parameterisation of that system. In this context, variability becomes an opportunity to: (i) better characterise typical versus atypical brain functions; (ii) reveal the different cognitive strategies and processing networks that can sustain similar tasks; and (iii) predict recovery capacity after brain damage by taking into account both damaged and spared processing pathways. This has many ramifications for understanding individual learning preferences and explaining the wide differences in human abilities and disabilities. Understanding variability boosts the translational potential of neuroimaging findings, in particular in clinical and educational neuroscience.

Cognition, personality, and stress in budgerigars, Melopsittacus undulatus

To study the fitness effects of individual variation in cognitive traits, it is paramount to understand whether traits such as personality and physiological stress influence cognitive performance. We first tested whether budgerigars showed both consistent personalities and cognitive performance across time and tasks. We tested object and food neophobia, and exploratory behavior. We measured cognitive performance in habituation, ability to solve foraging problems, spatial memory, and seed discrimination tasks. Budgerigars showed consistency in their neophobic tendencies and these tendencies were associated with their exploratory behavior. Birds were also consistent in how they performed in most of the cognitive tasks (temporal consistency), but were not consistent in their performance across tasks (context consistency). Neither corticosterone levels (baseline and stress-induced) showed a significant relationship with either cognitive or personality measures. Neophobic and exploratory tendencies determined the willingness of birds to engage only in the seed discrimination task. Such tendencies also had a significant effect on problem-solving ability. Our results suggest that consistent individual differences in cognitive performance along with consistent differences in personality could determine response to environmental change and therefore have important fitness consequences.

Cognitive test batteries in animal cognition research: evaluating the past, present and future of comparative psychometrics

For the past two decades, behavioural ecologists have documented consistent individual differences in behavioural traits within species and found evidence for animal "personality". It is only relatively recently, however, that increasing numbers of researchers have begun to investigate individual differences in cognitive ability within species. It has been suggested that cognitive test batteries may provide an ideal tool for this growing research endeavour. In fact, cognitive test batteries have now been used to examine the causes, consequences and underlying structure of cognitive performance within and between many species. In this review, we document the existing attempts to develop cognitive test batteries for non-human animals and review the claims that these studies have made in terms of the structure and evolution of cognition. We argue that our current test battery methods could be improved on multiple fronts, from the design of tasks, to the domains targeted and the species tested. Refining and optimising test battery design will provide many benefits. In future, we envisage that well-designed cognitive test batteries may provide answers to a range of exciting questions, including giving us greater insight into the evolution and structure of cognition.

do Monte BG, Watanabe IM, Cunha J, Peripato AC. A link between thrifty phenotype and maternal care across two generations of intercrossed mice

Maternal effects are causal influences from mother to offspring beyond genetic information, and have lifelong consequences for multiple traits. Previously, we reported that mice whose mothers did not nurse properly had low birth weight followed by rapid fat accumulation and disturbed development of some organs. That pattern resembles metabolic syndromes known collectively as the thrifty phenotype, which is believed to be an adaptation to a stressful environment which prepares offspring for reduced nutrient supply. The potential link between maternal care, stress reactivity, and the thrifty phenotype, however, has been poorly explored in the human and animal literature: only a couple of studies even mention (much less, test) these concepts under a cohesive framework. Here, we explored this link using mice of the parental inbred strains SM/J and LG/J–who differ dramatically in their maternal care–and the intercrossed generations F1 and F2. We measured individual differences in 15 phenotypes and used structural equation modeling to test our hypotheses. We found a remarkable relationship between thrifty phenotype and lower quality of maternal behaviors, including nest building, pup retrieval, grooming/licking, and nursing. To our knowledge, this is the first study to show, in any mammal, a clear connection between the natural variation in thrifty phenotype and maternal care. Both traits in the mother also had a substantial effect on survival rate in the F3 offspring. To our surprise, however, stress reactivity seemed to play no role in our models. Furthermore, the strain of maternal grandmother, but not of paternal grandmother, affected the variation of maternal care in F2 mice, and this effect was mediated by thrifty phenotype in F2. Since F1 animals were all genetically identical, this finding suggests that maternal effects pass down both maternal care and thrifty phenotype in these mice across generations via epigenetic transmission.

The external-internal loop of interference: two types of attention and their influence on the learning abilities of mice

Attention is a component of the working memory system, and is responsible for protecting task-relevant information from interference. Cognitive performance (particularly outside of the laboratory) is often plagued by interference, and the source of this interference, either external or internal, might influence the expression of individual differences in attentional ability. By definition, external attention (also described as "selective attention") protects working memory against sensorial distractors of all kinds, while internal attention (also called "inhibition") protects working memory against emotional impulses, irrelevant information from memory, and automatically-generated responses. At present, it is unclear if these two types of attention are expressed independently in non-human animals, and how they might differentially impact performance on other cognitive processes, such as learning. By using a diverse battery of four attention tests (with varying levels of internal and external sources of interference), here we aimed both to explore this issue, and to obtain a robust and general (less task-specific) measure of attention in mice. Exploratory factor analyses revealed two factors (external and internal attention) that in total, accounted for 73% of the variance in attentional performance. Confirmatory factor analyses found an excellent fit with the data of the model of attention that assumed an external and internal distinction (with a resulting correlation of 0.43). In contrast, a model of attention that assumed one source of variance (i.e., "general attention") exhibited a poor fit with the data. Regarding the relationship between attention and learning, higher resistance against external sources of interference promoted better new learning, but tended to impair performance when cognitive flexibility was required, such as during the reversal of a previously instantiated response. The present results suggest that there can be (at least) two types of attention that contribute to the common variance in attentional performance in mice, and that external and internal attentions might have opposing influences on the rate at which animals learn.

The Architecture of Intelligence

A person’s performance across multiple cognitive tests tends to covary. This ubiquitous observation suggests that various cognitive domains are regulated in common, and this covariance underlies the interpretation of many quantitative tests of “intelligence.” We find that, as in humans, differences in intelligence exist across genetically heterogeneous mice. Specifically, we have observed a covariance in the performance of mice across diverse tests of learning, reasoning, and attention. As in humans, the processing efficacy of working memory is both correlated with animals’ general cognitive abilities and may in some instances serve to regulate behaviors indicative of intelligence. Beyond its axiomatic significance in demonstrating the evolutionary conservation of a cognitive trait, studies of mice may provide unique opportunities to assess the molecular (e.g., brain-specific RNA expression; transgenics) and neuroanatomic substrates for intelligence. One such approach is briefly described here. Using this approach, we have determined that the signaling efficacy of the dopamine D1 receptor in the prefrontal cortex is one potential link between performance on both working-memory tasks and tests of intelligence. In combination, studies of both humans and nonhuman animals provide converging lines of evidence that might evade either approach in isolation.