Environmentally induced changes to brain morphology predict cognitive performance.

Cognition, the process by which animals acquire, process, store and use information from their environment, plays a major role in various behaviours across all aspects of an individuals’ life. However, despite this overall importance of cognitive abilities, we still know little about how cognitive traits evolved. In the past, research on cognitive evolution focussed on comparing different species in their cognitive abilities and linked variation in cognition to inter-specific differences in ecological and social conditions. This comparative approach helps to understand when in evolutionary history and under which conditions particular cognitive abilities evolved. Individual variation in cognitive abilities has been widely ignored in these studies on the species level, however. This changed only recently when the interest in how and why individuals differ in cognitive traits emerged. Only by investigating inter-individual variation in cognitive abilities and their link with fitness outcomes, we can begin to understand the causes and consequences of this variation and finally unravel how cognition evolved. Because fitness can only be studied in wild, free-ranging individuals, the study of individual differences in cognitive abilities and their fitness consequences is challenging and has been conducted mainly in different species of birds until today. The few studies so far focused largely on single measures of cognition and fitness and revealed not only positive but also negative and not significant correlations between cognitive performance and fitness outcomes. With my thesis, I contribute to this young field of research aiming to better understand the adaptive value of cognitive traits. I investigated cognitive abilities in five cognitive tasks in wild grey mouse lemurs (Microcebus murinus), a primate species endemic to Madagascar, and linked cognitive performance with different fitness proxies. The cognitive tasks addressed different ecologically relevant cognitive abilities. They included associative and motor learning during repeated problem solving, causal reasoning and spontaneous problem solving in a string-pulling task, spatial learning, inhibitory control and behavioural flexibility during reversal learning. Subjects were tested during short-term captivity of up to three nights and subsequently released back into the wild. Furthermore, individuals were tested in two personality tests and their neophilia and activity during a novel object and an open field test was assessed. In the first part of my thesis, I focused on inter- and intra-individual differences of cognitive performance: the potential confounding effects of non-cognitive factors on cognitive performance and the structure of cognitive performance across different cognitive abilities. My results demonstrated that, first of all, subjects differed greatly in cognitive performance and performance was not systematically affected by non-cognitive factors such as personality, body condition, motivation, age or sex. Furthermore, performance in one cognitive task was generally a weak predictor of performance in any other tasks of the test battery and could not be summarized into a general factor. Thus, I could not find evidence for a general factor of cognitive performance similar to the general intelligence factor (g) in humans, where performance is positively correlated across cognitive tasks and domains. In the second part of the thesis, I studied different fitness-related traits in grey mouse lemurs and linked cognitive performance with two fitness proxies. I found that efficient repeated solving of a food extraction task correlated positively with the ability to maintain body condition during the long dry season with low food availability. This suggests that the ability to quickly apply a newly discovered motor technique during problem solving also facilitates the exploitation of new, natural food resources when food is scarce. By contrast, cognitive performance, irrespective of cognitive task, did not correlate with survival or longevity, suggesting that the assessed cognitive abilities did not provide (net) benefits in survival. Moreover, difficulties in validating a physiological condition factor, that summarized measures of body condition, hematocrit and long-term cortisol levels, demonstrated that identifying and operationalizing meaningful fitness proxies can be challenging for many taxa. In summary, my thesis contributes the first study on a wild primate to the growing body of research investigating individual differences in cognitive abilities and their link with fitness outcomes. Together with the other recent findings revealing heterogenous links between cognitive performance and fitness measures, my thesis demonstrates that cognitive abilities are involved in complex interactions between various traits. At the same time, they are likely to have costs and benefits, and thus do not necessarily correlate positively with fitness outcomes. Further studies in different species in the wild, that investigate multiple cognitive traits and fitness outcomes as well as potentially confounding covariates simultaneously, will help to unravel this complex system, the evolution of cognition.

Recent studies on the differences in cognitive ability between individuals focused on two aspects: one is whether the individual differences in cognitive ability are related to brain size, the other is whether they pertain to certain personality traits. To explore these two hypotheses, we tested the personality traits, cognitive abilities, and brain volumes of western mosquitofish (Gambusia affinis). First, a color preference test was conducted to select two unbiased colors for G. affinis for subsequent cognitive tests. The results showed that G. affinis had a great preference for red and green to yellow and blue; therefore, the red-green combination was selected for the study of cognitive abilities. Then, we explored the relationship among cognition, personality, and brain morphology through cognitive abilities tests, personality traits, and brain volume measurements. We found that there was a trade-off among cognition, personality, and brain morphology. For example, more active individuals found food faster, but had also poor memory; Those individuals with larger corpus cerebelli were bolder while they were less likely to find food; The individuals that found food faster were more active and had a smaller inferior lobe. The color preference test provides a reliable way for selecting unbiased colors for behavioral studies in G. affinis. Meanwhile, our study indicates that there exists a balance mechanism among cognition, personality, and brain morphology.

Cognitive Psychology (CP) in the last 50 years has shown impressive development, producing a large body of data mainly concerned with specific elements of the complex cognitive architecture of the mind. The focus on single processes, in large part necessarily narrow and detailed, has not prevented the development of general concepts, paradigms, and models that can be useful to all areas of psychology. In fact, since the mind’s operations typically studied by CP, such as memory, attention, language, reasoning, and so on, are the basis for every psychological activity and behaviour, their scientific analysis can be used by other associated areas of study, for example Social Psychology, Clinical Psychology, Applied Psychology, Educational Psychology, Developmental Psychology, etc. Indeed, we are observing in these areas an increasing interest in concepts emerging from CP. The potential contribution of CP to the study of human intelligence is particularly representative and interesting. In fact, the consideration of individual differences in cognitive abilities and, in particular, in intelligence is one of the main topics that should be covered by CP. But this has not been the case for many years. Despite its obvious importance, the concept of intelligence has been suspiciously considered by many researchers and in particular by researchers working in the cognitive area. An implicit consideration has been that the concept ‘‘intelligence’’ is ill-defined and lacks an association with a well-supported research tradition. The misleading and circular definition of ‘‘intelligence’’, as the dimension measured by intelligence tests, was considered representative of the theoretical poverty of the field. For this reason the study of intelligence was mainly left to psychologists working in the psychometric tradition and to a certain extent the field of developmental psychology. However there are now signs that the time has come for CP to make a more substantial contribution to the study of individual differences in intelligence and other related cognitive abilities.

Cognitive abilities probably evolve through natural selection if they provide individuals with fitness benefits. A growing number of studies demonstrate a positive relationship between performance in psychometric tasks and (proxy) measures of fitness. We assayed the performance of 154 common pheasant (Phasianus colchicus) chicks on tests of acquisition and reversal learning, using a different set of chicks and different set of cue types (spatial location and colour) in each of two years and then followed their fates after release into the wild. Across all birds, individuals that were slow to reverse previously learned associations were more likely to survive to four months old. For heavy birds, individuals that rapidly acquired an association had improved survival to four months, whereas for light birds, slow acquirers were more likely to be alive. Slow reversers also exhibited less exploratory behaviour in assays when five weeks old. Fast acquirers visited more artificial feeders after release. In contrast to most other studies, we showed that apparently ‘poor’ cognitive performance (slow reversal speed suggesting low behavioural flexibility) correlates with fitness benefits in at least some circumstances. This correlation suggests a novel mechanism by which continued exaggeration of cognitive abilities may be constrained.This article is part of the theme issue ‘Causes and consequences of individual differences in cognitive abilities’.

Intracranial space-occupying lesions (ISOLs) are common pediatric conditions. Recent therapeutic advances have significantly improved survival rates, necessitating increased attention to post-operative cognitive outcomes, which are crucial determinants of patients' quality of life. While previous studies have predominantly focused on short-term post-operative changes, this study aimed to investigate longitudinal changes in cognition, brain structure, and function of the contralateral hemisphere following pediatric neurosurgery. Nineteen pediatric patients with ISOLs were enrolled in a paired design study. Cognitive assessments, structural imaging, and functional imaging data were collected at three time points: pre-operation, first post-operative follow-up (mean 75 days pre-operation), and second post-operative follow-up (mean 316 days pre-operation). Relevant metrics were computed and compared across time points. The majority of cognitive domains exhibited a gradual longitudinal improvement trajectory, with three domains showing significant enhancement at the second follow-up compared to preoperative baseline: cognitive flexibility (t = 4.201, p = 0.001), executive function (t = 3.478, p = 0.003), and social accuracy (t = 3.248, p = 0.004). The contralesional hemisphere demonstrated alterations primarily characterized by gray matter density reduction, progressing from subcortical structures (first follow-up: thalamus, peak intensity = -7.54, cluster p < 0.016) to cortical regions (second follow-up compared to previous follow-up: superior frontal gyrus, peak intensity = -7.80, cluster p < 0.016), followed by a subsequent increase in brain activity power of smaller magnitude (second follow-up: medial superior frontal gyrus, amplitude of low frequency fluctuation, peak intensity = 5.96, cluster p < 0.016). Correlation analysis suggests that there is an association between changes in brain structure and alterations in cognitive function (r = -0.53, p = 0.019). Our findings suggest that post-craniotomy structural and functional brain changes in children follow a subcortical-to-cortical trajectory, with structural alterations (decreased gray matter density) preceding functional activation. This process demonstrates progressive and cumulative characteristics. These modifications appear to correlate with cognitive function recovery and may represent potential mechanisms underlying spontaneous cognitive rehabilitation in pediatric patients post-surgery. Cautiously interpreted, the deeper neuroplastic mechanisms underlying these changes might involve synaptic pruning-like processes induced by external perturbation.

Natural selection is a major force in the evolution of vertebrate brain size, but the role of sexual selection in brain size evolution remains enigmatic. At least two opposing schools of thought predict a relationship between sexual selection and brain size. Sexual selection should facilitate the evolution of larger brains because better cognitive abilities may aid the competition for mates. However, it may also restrict brain size evolution due to energetic trade‐offs between brain tissue and sexually selected traits. Here, we examined the patterns of selection on brain size and brain anatomy in male anurans (frogs and toads), a group where the strength of sexual selection differs markedly among species, using a phylogenetically controlled generalized least‐squared (PGLS) regression analyses. The analysis revealed that in 43 Chinese anuran species, neither mating system, nor type of courtship, or testes mass was significantly associated with relative brain size. While none of those factors related to the relative size of olfactory nerves, optic tecta, telencephalon, and cerebellum, the olfactory bulbs were relatively larger in monogamous species and those using calls during courtship. Our findings support the mosaic model of brain evolution and suggest that while the investigated aspects of sexual selection do not seem to play a prominent role in the evolution of brain size of anurans, they do impact their brain anatomy.

The effects of air pollution on sleep and dementia remain unclear. The objective of this study was to investigate the effects of air pollution on cognitive function as mediated by the sleep cycle. A cross-sectional study design was conducted to recruit 4866 subjects on which PSG had been performed. Fifty of them were further given a cognitive function evaluation by the MMSE and CASI as well as brain images by CT and MRI. Associations of 1-year air pollution parameters with sleep parameters, cognitive function, and brain structure were examined. We observed that O3 was associated with a decrease in arousal, an increase in the N1 stage, and a decrease in the N2 stage of sleep. NO2 was associated with an increase in the N1 stage, a decrease in the N2 stage, and an increase in REM. PM2.5 was associated with a decrease in the N1 stage, increases in the N2 and N3 stages, and a decrease in REM. The N1 and N2 stages were associated with cognitive decline, but REM was associated with an increase in cognitive function. The N1 stage was a mediator of the effects of PM2.5 on the concentration domain of the MMSE. O3 was associated with an increase in the pars orbitalis volume of the left brain. NO2 was associated with increases in the rostral middle frontal volume, supramarginal gyrus volume, and transverse temporal volume of the left brain, and the pars opercularis volume of the right brain. PM2.5 was associated with increases in the pars triangularis volume of the left brain and the fusiform thickness of the right brain. In conclusion, we observed that air pollution was associated with cognitive decline by mediating effects on the sleep cycle with changes in the brain structure in controlling executive, learning, and language functions in adults.

The capacity to deliberately control attention in order to hold and manipulate information in working memory is critical to higher cognitive functions. This suggests that between-subject differences in general cognitive ability might be related to observable differences in the activity of brain systems that support working memory and attention control. To test this notion, electroencephalograms were recorded from 80 healthy young adults during spatial working memory tasks. Measures of task-related neurophysiological and behavioral variables were derived from these data and compared to scores on a test battery commonly used to assess general cognitive ability (the WAIS-R). Subjects who scored high on the psychometric test also tended to respond faster in the experimental tasks without any loss of accuracy. The amplitude of the late positive component of the event-related potential was larger in high-ability subjects, and the frontal midline theta component of the EEG signal was also selectively enhanced in this group under conditions of sustained performance and high working memory load. These results suggest that subjects who scored high on the WAIS-R were better able to focus and sustain attention to task performance. Changes in the EEG alpha rhythm in response to manipulations of task practice and load were also examined and compared between frontal and parietal regions. The results indicated that high-ability subjects developed strategies that made relatively greater use of parietal regions, whereas low-ability subjects relied more exclusively on frontal regions. Other analyses indicated that hemispheric asymmetries in alpha band measures distinguish between individuals with relatively high verbal aptitude and those with relatively high nonverbal aptitude. In particular, subjects with a verbal cognitive style tended to make greater use of the left parietal region during task performance, and subjects with a nonverbal style tended to make greater use of the right parietal region. These results help clarify relationships between task-related brain activity and individual differences in cognitive ability and style.

Educational attainment in adolescence is of paramount importance for attaining higher education and for shaping subsequent life chances. Sociological accounts focus on the role of differences in socioeconomic resources in intergenerational reproduction of educational inequalities. These often disregard the intergenerational transmission of cognitive ability and the importance of children's cognitive ability to educational attainment. Psychological perspectives stress the importance of cognitive ability for educational attainment but underemphasize potentially different roles of specific socioeconomic resources in shaping educational outcomes, as well as individual differences in cognitive ability. By integrating two strands of research, a clearer picture of the pathways linking the family of origin, cognitive ability, and early educational outcomes can be reached. Using the population-based TwinLife study in Germany, we investigated multidimensional pathways linking parental socioeconomic position to their children's cognitive ability and academic track attendance in the secondary school. The sample included twins (N = 4008), respectively ages 11 and 17, and siblings (N = 801). We observed strong genetic influences on cognitive ability, whereas shared environmental influences were much more important for academic tracking. In multilevel analyses, separate dimensions of socioeconomic resources influenced child cognitive ability, controlling parental cognitive ability. Controlling adolescent cognitive ability and parental cognitive ability, parental socioeconomic resources also directly affected track attendance. This indicated that it is crucial to investigate the intertwined influences on educational outcomes in adolescence of both cognitive ability and the characteristics of the family of origin.

Variation in cognitive abilities is thought to be linked to variation in brain size, which varies across species with either social factors (Social Intelligence Hypothesis) or ecological challenges (Ecological Intelligence Hypothesis). However, the nature of the ecological processes invoked by the Ecological Intelligence Hypothesis, like adaptations to certain habitat characteristics or dietary requirements, remains relatively poorly known. Here, we review comparative studies that experimentally investigated interspecific variation in cognitive performance in relation to a species’ degree of ecological specialisation. Overall, the relevant literature was biased towards studies of mammals and birds as well as studies focusing on ecological challenges related to diet. We separated ecological challenges into those related to searching for food, accessing a food item and memorising food locations. We found interspecific variation in cognitive performance that can be explained by adaptations to different foraging styles. Species-specific adaptations to certain ecological conditions, like food patch distribution, characteristics of food items or seasonality also broadly predicted variation in cognitive abilities. A species’ innovative problem-solving and spatial processing ability, for example, could be explained by its use of specific foraging techniques or search strategies, respectively. Further, habitat generalists were more likely to outperform habitat specialists. Hence, we found evidence that ecological adaptations and cognitive performance are linked and that the classification concept of ecological specialisation can explain variation in cognitive performance only with regard to habitat, but not dietary specialisation.

BackgroundWhile extensive research has examined brain‐behavior relationships in cognitive decline, far less study of the other extreme has been done with super‐agers or those with extraordinary abilities. Harold Coxeter (HC), an extraordinary geometrician (Figure 1), considered one of the foremost mathematical minds of the 20th century, volunteered to have his brain studied after learning about the neuroanatomical analysis of Albert Einstein's brain (Witelson et al., 1999). We aimed to explore whether HC's exceptional geometrical prowess was related to variations in brain anatomy, particularly the parietal lobes.MethodAt the age of 93, HC underwent structural MRI, which was analyzed using Semi‐Automated Brain Region Extraction (SABRE) and FreeSurfer (Figure 2). Brain images were compared to 24 neurotypical men of senior age. Grey matter (GM) and white matter (WM) volumes were assessed in HC and controls, focusing on key regions associated with mathematical cognition and spatial abilities.ResultNo significant differences in GM volumes were observed between HC and controls in any region, based on both SABRE and FreeSurfer analyses. However, HC exhibited larger WM volumes in several brain regions, notably in the right and left superior parietal regions, as well as the left superior frontal, left occipital, and right posterior temporal regions, where HC's white matter volume exceeded the control group mean by at least two standard deviations (Figure 3). Moreover, his WM volumes were greater than that of any individual control.ConclusionThe findings suggest that HC's exceptional abilities may be associated with increased connectivity mediated by WM tracts in specific brain regions, particularly those related to visuospatial processing and mathematical cognition. These results support the general hypothesis that WM connectivity may play a key role in intelligence variability, especially in domains involving spatial and mathematical processing. We found no evidence for GM differences. Some other studies of cognitive expertise showed increased GM density, but used transformed measures of relative GM density, whereas our method allows direct quantification of tissue volumes. This study highlights the potential link between structural brain differences and variations in cognitive ability, offering insight into the neurobiological basis of some aspects of human intelligence.

Rapid individual cognitive phenotyping holds the potential to revolutionize domains as wide-ranging as personalized learning, employment practices, and precision psychiatry. Going beyond limitations imposed by traditional lab-based experiments, new efforts have been underway toward greater ecological validity and participant diversity to capture the full range of individual differences in cognitive abilities and behaviors across the general population. Building on this, we developed Skill Lab, a novel game-based tool that simultaneously assesses a broad suite of cognitive abilities while providing an engaging narrative. Skill Lab consists of six mini-games as well as 14 established cognitive ability tasks. Using a popular citizen science platform (N = 10,725), we conducted a comprehensive validation in the wild of a game-based cognitive assessment suite. Based on the game and validation task data, we constructed reliable models to simultaneously predict eight cognitive abilities based on the users' in-game behavior. Follow-up validation tests revealed that the models can discriminate nuances contained within each separate cognitive ability as well as capture a shared main factor of generalized cognitive ability. Our game-based measures are five times faster to complete than the equivalent task-based measures and replicate previous findings on the decline of certain cognitive abilities with age in our large cross-sectional population sample (N = 6369). Taken together, our results demonstrate the feasibility of rapid in-the-wild systematic assessment of cognitive abilities as a promising first step toward population-scale benchmarking and individualized mental health diagnostics.

Age-related decline in cognitive control and general slowing are prominent phenomena in aging research. These declines in cognitive functions have been shown to also involve age-related decline in brain structure. However, most evidence in support of these associations is based on cross-sectional data. Therefore, the aim of this study is to contrast cross-sectional and longitudinal analyses to re-examine if the relationship between age-related brain structure and cognitive function are similar between the two approaches. One hundred and two participants completed two sessions with an average interval of 2 years. All participants were assessed by questionnaires, a series of cognitive tasks, and they all underwent neuroimaging acquisition. The main results of this study show that the majority of the conclusions regarding age effect in cognitive control function and processing speed in the literature can be replicated based on the cross-sectional data. Conversely, when we followed up individuals over an average interval of 2 years, then we found much fewer significant relationships between age-related change in gray matter structure of the cognitive control network and age-related change in cognitive control function. Furthermore, there was no “initial age” effect in the relationships between age-related changes in brain structure and cognitive function. This finding suggests that the “aging” relationship between brain structure and cognitive function over a short period of time are independent of “initial age” difference at time point 1. The result of this study warrants the importance of longitudinal research for aging studies to elucidate actual aging processes on cognitive control function.

This chapter discusses the brain structural changes arising from fetal alcohol exposure. It argues that teratogenic exposure to alcohol causes permanent changes in brain structure and differentially affects specific components and regions of the brain. These structural changes likely underlie deficits in the cognitive ability and adaptive functioning of exposed individuals. Structural brain deficits revealed by quantitative image analyses of alcohol-exposed individuals include reductions in overall brain volume and alterations in brain shape, density, and bilateral symmetry.

Influence of a sensorimotor conflict on the memorization of a path traveled in virtual reality