Early-life adversity and adult cognition: the starling as an experimental model.

People who experience a harsh environment in early life - for example, low birthweight, family poverty or family disruption - are more likely to experience depression, addictions and behavioural problems years later when they are adults. This suggests that harsh early conditions induce a cognitive style involving increased pessimism and impulsivity. The human evidence for such effects is necessarily correlational. To show experimentally that there is a causal relationship, an animal model is required.

In this project, we will develop a novel animal model for studying the effects of early-life conditions on adult cognition, using European starlings. Starlings have many advantages; they are long-lived, wild animals, for whom cognitive measures in the laboratory have already been developed. Most importantly, we can experimentally manipulate the harshness of the early environment in a natural setting, by either reducing the number of chicks in a nest to 2, or increasing to 7. We will create 32 enlarged and 32 reduced nests at farms in Northumberland, and take one chick from each into the laboratory, where we will use established cognitive tasks to examine pessimism and impulsivity. These tasks involve the animal having to interpret an ambiguous stimulus as either positive or negative (for pessimism), and having to choose between immediate and deferred rewards (for impulsivity). We will also examine the extent to which a positive current environment can compensate for harsh conditions in early-life, by housing half of our birds in barren and half in enriched conditions during the testing phase. In addition, we will use a number of biological measures to explore the mechanisms underlying the impact of early-life conditions on adult phenotype. These are growth profile, responsivity of the stress hormone corticosterone, oxidative stress and telomere length. Each of these has been implicated in how early events impact on adults, in humans as well as other animals.

This study will constitute the first experimental evidence for an impact of early-life events on adult pessimism and impulsivity, and will begin to elucidate the mechanisms involved. The results have important implications for understanding the causes of the excess burden of depression, addictions and conduct disorder in deprived communities, and will help understand the extent to which a positive adult environment can mitigate the effects of early-life environment.

Exposure to early-life adversity is correlated with a range of psychological problems in adult humans, including affective disorders and addictions. We hypothesise that the common cognitive mechanisms underlying many of these effects are increased pessimism and impulsivity. In this project we aim to show experimentally that there is a causal relationship between early-life adversity and increased pessimism and impulsivity. We will develop a novel animal model using European starlings for studying the effects of early-life conditions on adult cognition. Starlings have the advantage of being long-lived, wild animals, for which measures of pessimism and impulsivity have already been developed. Importantly, we can manipulate the harshness of the early environment in the wild by a brood size manipulation. We will create 32 enlarged and 32 reduced broods, and, at fledging, take one chick from each nest into the lab, where we will examine pessimism (using a judgement bias task) and impulsivity (using a delayed reinforcement choice task). We will also examine the effects of perceived threat in the current environment by housing half the birds in barren and half in enriched cages during the testing phase. In addition, we will measure a number of biological variables to explore the mechanisms underlying the impact of brood size on adult phenotype. These include growth profile, corticosterone levels (baseline and response to acute capture-restraint stress), oxidative stress and telomere length. Each of these has been implicated in how early events impact adults in humans and birds. Our results will constitute the first experimental evidence for an impact of early-life events on adult pessimism and impulsivity, and will begin to elucidate the mechanisms involved. Our results will have implications for understanding the causes of the excess burden of depression and addiction in deprived communities, and the role of the adult environment in these effects.

Several communities of scientific researchers will benefit from the proposed project, as outlined in Academic Beneficiaries above. In addition, it will have broader benefits for society, through its relevance to human psychiatric disorders, and through its implications for the study of animal welfare.

In recent years, there has been increased focus by governments on the psychological wellbeing of their citizens, and the social discrepancies in pessimism and impulsivity account for a significant fraction of the social variation in the burden of conditions such as depression and conduct disorder. Thus, having direct causal evidence on the impact of early-life environment on pessimism and impulsivity would help policy-makers, and charitable organisations, decide about the allocation of resources towards interventions which improve children's very early environments, rather than other kinds of interventions. Thus, the knowledge created here has potential to impact on public health policy, and, ultimately, the psychological wellbeing of society as a whole. To facilitate this, we propose to write a review article of the evidence from avian behavioural ecology for the impact of early-life environment on adult phenotype, including but not limited to the brain (see Pathways to Impact).

From the animal welfare side, the central problem in animal welfare is knowing when animals' wellbeing is compromised and when it is not. The measures this grant helps to develop, such as cognitive bias, telomere length, and impulsivity, will be added to the armamentarium of researchers, policy-makers, and welfare charities, to aid in the evidence-based resolution of welfare questions. We propose to write a synthetic article targeted at the welfare community to spread knowledge about these measures and their utility (see Pathways to Impact).

The aim of this project is to create fundamental basic knowledge concerning the impact of developmental history on adult cognition. Thus, the wider societal impacts described above will not be realised within the lifetime of the grant, but rather through the cumulative long-term impact of having a solid experimental model of these processes, published in peer-reviewed scientific papers, and available for other researchers to build upon.