Editorial: ‘The people they are a changin’ – overview of the 2024 Annual Research Review

Two years ago, the title of my editorial (with thanks to Edmund Sonuga-Barke and Bob Dylan) was ‘The times they are a-changin’. This title was meant to highlight the paradigm shifts in the field reflected in the papers included in that year's Annual Research Review. This year's editorial is instead titled ‘The people, they are a-changin’. This is because, overwhelmingly, the papers in the 2024 Annual Research Review describe how people and systems change each other, how people change over developmental and historical time, and how environments characterized by change impact human development.

One way in which people change over time is in the degree to which they manifest symptoms of psychopathology, with certain disorders likely to emerge at particular points in development. This observation is at the core of research in developmental psychopathology and psychiatric epidemiology. Why, for example, do rates of depression spike in adolescence, particularly for girls? In search of mechanisms, researchers have identified interpersonal, cognitive, and biological factors (see commentary by Shanahan and Copeland). Gupta, Eckstrand, and Forbes introduce an integrative model to explain the emergence in adolescence of symptoms of anhedonia – a core feature of depression, characterized by diminished experience of pleasure and motivation to pursue rewards. They hypothesize that anhedonia may be the result of chronic inflammation in response to childhood adversity that influences the development of frontostriatal and dopamine circuitry during puberty. The authors describe evidence from animal and human studies that these neural circuits underlie our motivation to pursue and experience rewards and present data showing that proinflammatory molecules contribute to dopamine availability and alterations in ventrostriatal response to reward.

Additional evidence for this conceptual model linking early adversity, chronic immune activation, and neural circuitry is provided by Nusslock et al., who, like Gupta et al., present an integrative model that crosses biological and behavioral accounts of psychopathology. The neuroimmune network model of physical and mental health describes interactions between proinflammatory molecules (e.g., monocytes and cytokines) and neural circuitry underlying threat sensitivity, anticipation of and response to reward, executive function, and emotion regulation. These neuroimmune interactions are hypothesized to underlie symptoms of anhedonia and dysphoria that are implicated transdiagnostically. Moreover, the neuroimmune network model acknowledges the role of health risk behaviors that can arise in response to anhedonia, dysphoria, and distress and that also increase the risk for poor mental and physical health. This review, like Gupta et al., describes adolescence as a period of vulnerability for anhedonia and depression resulting from neuroimmune interactions and it extends the discussion of the conceptual model to its implications for comorbidity between depression and other psychiatric disorders as well as multimorbidity with other medical illnesses.

These papers by Gupta et al. and Nusslock et al. highlight puberty as a sensitive period for the development of anhedonia, dysphoria, and distress, in part because it is a window of heightened brain plasticity. Nelson et al. focus on an earlier period of rapid brain development – the first 3 years of life – and discuss the implications of conducting interventions when the brain is being actively constructed. Nelson et al. review the evidence that the brain does, in fact, change in response to early intervention, with a particular focus on early intervention services for children growing up in disadvantaged environments and for children at risk of neurodevelopmental delay. Findings not only demonstrate short-term effects of early intervention on indices of healthy brain development but, in some cases, also demonstrate enduring effects. In the accompanying commentary, Romeo points to the need for a parallel program of research on interventions that target social determinants of health (e.g., cash transfer programs, programs to promote housing, or food security), given that these interventions are hypothesized to have positive trickle-down effects on children's brain development and because these programs can potentially be scaled up more easily than intensive behavioral interventions can be. Taken together, the papers focusing on brain plasticity identify at least two windows – early childhood and puberty – when developmentally appropriate interventions may be optimally effective at setting or restoring normative trajectories.

The papers reviewed in the previous section describe how individuals change over time, developing symptoms or recovering with the help of intervention. In contrast, Keyes and Platt describe how populations change over historical time, highlighting increasing rates of depression over the past two to three decades, particularly for girls. Why are young people – and particularly girls – becoming more and more depressed with each subsequent generation? Rather than reviewing all possible explanations (although they review many), Keyes and Platt present an epidemiological framework for evaluating the evidence for putative explanatory factors. Specifically, they note that the potential explanatory mechanism must be associated with internalizing psychopathology and that it must have become increasingly prevalent or increasingly virulent over the past several decades. Finally, to adequately account for changes over time in gender differences in internalizing disorders, it must either be true that girls are more exposed than boys to the explanatory mechanism or, if their exposure is not greater, they are more adversely affected by it. Keyes and Platt then review evidence for a number of known risk factors for internalizing disorders (e.g., stressful life events, puberty, hormones, etc.), applying the epidemiological framework to evaluate whether these are plausible explanations for trends over time, including trends in anxiety and suicidal behavior.

Another example of how populations change over time is represented in the paper by Wang et al, who report that the number of children residing in grandfamilies (i.e., families in which grandparents are the primary caregivers) is growing worldwide. This shift in caregiving reflects demographic changes in aging and in women's labor force participation across the globe. These researchers ask whether this trend in who is caring for children has implications for children's mental health. The results of their meta-analysis show that children cared for by their grandparents have poorer mental health than children not cared for by grandparents, although effect sizes were small in magnitude. This study generates many questions for future research including whether these associations arise from how grandparents provide care for children or whether they primarily reflect the fact children who are cared for by grandparents are more socially disadvantaged than children whose parents are their primary caregivers.

Finally, although the paper by Rask et al. is not explicitly about secular change, it is likely that researchers will focus on 2020 and the onset of the COVID-19 pandemic as an inflection point for symptoms of health anxiety in the population. Rask et al. focus specifically on pediatric health anxiety, characterized by excessive worries about one's current or future health. Their review highlights a problem that may be more common in childhood than the data would suggest given the lack of developmentally appropriate assessments. Like the papers described in the following section, the Rask et al. review highlights the dyadic nature of pediatric health anxiety, emphasizing intergenerational continuities in symptoms of anxiety and the implications for how caregivers co-regulate children's arousal in response to bodily sensations.

John Donne famously wrote ‘No man is an island, Entire of itself’ emphasizing the importance of human connection. The paper by Wass et al. describes the importance of connections in early life between the caregiver and the infant. Wass et al. emphasize the critical role of co-regulation, which they define as a dyadic process designed to ‘maintain an optimal level of Central Nervous System (CNS) arousal, intermediate between under- and over-excitation’. This process is inherently dynamic, with the infant and caregiver's behavior at any point in time contingent on the behavior of each at the previous moment. An important contribution of this paper is its exploration of co-regulation over time and over multiple time scales. In contrast to conventional accounts of child development that describe how passive and active co-regulatory processes ultimately give way to self-regulation, Wass et al. propose that co-regulation is a key process throughout development – one that becomes increasingly elaborated to shape social–emotional, social-communicative, and cognitive function and that shifts from an asymmetric, unidirectional process in early development (with the caregiver adapting to the child more than the reverse) to one that is truly bidirectional later in development.

Interestingly, several of the papers in the 2024 Annual Research Review adopt a dynamic systems perspective. For example, Nusslock et al., describe the communication among organ systems (e.g., immune and central nervous systems) whereby neural circuitry adapts to inflammation, leading to symptoms of dysphoria and anhedonia. These symptom states can, in turn, result in unhealthy coping behaviors that induce more inflammation, ultimately creating positive feedback loops. The discussion of dynamic systems models diverges in important ways, however, in the context of multiple organ systems versus dyadic co-regulation. Nusslock et al. observe that dysregulation of the immune system (as reflected in chronic inflammation) arises from what is initially a normative immune process: activation in response to psychosocial threat. Thus, the immune system shifts from regulation to dysregulation over time as a result of chronic activation. In contrast, although Wass et al. propose that passive and active co-regulatory processes are implicated in both regulation and dysregulation, the active processes that lead to optimal arousal (i.e., compensatory adult behaviors to correct for the infant or toddler moving away from a critical state) are entirely different from the active processes that lead to dysregulation (i.e., changes in adult behavior that move the child even further from the critical state). As one example of this process, Rask et al. describe how excessive health worries in children may emerge from interactions with anxious parents who, rather than down-regulating their child's anxious arousal in response to benign physiological sensations, instead amplify it.

Although many of the papers in the 2024 Annual Research Review are about the ways in which people change over an individual lifetime, over historical time, or in time with each other, the paper by Davis and Glynn describes how environments change from moment to moment, from day to day, and over longer time periods. Whether or not we can predict these changes has important implications for healthy development. Davis and Glynn review a large body of evidence on the many forms of unpredictability that children experience, including housing instability and household chaos, caregiver changes, and unstable parental mental health. One of the novelties of this review is the emphasis on time scale, with a particular focus on moment-to-moment interactions between young children and caregivers. Davis and Glynn propose that there are sensitive periods when the developing brain benefits from predictable sensory inputs from caregivers, as measured on this time-scale. They describe evidence that children whose caregivers engage in unpredictable patterns of tactile, visual, or auditory signals have poorer scores on test of memory and cognitive control than children whose caregivers engage in more predictable patterns. As related to the review by Nelson et al. on early intervention, these findings suggest that interventions for children growing up in disadvantaged environments may be successful because they increase the predictability of signals between children and caregivers, leading to phenotypes (e.g., flexible cognitive control) that reduce risk for psychopathology transdiagnostically.

Shifting to the personal, I am stepping down in my role as Annual Research Review editor and passing the baton to Professor Daniel Shaw, whom I am confident will take this annual issue in exciting new directions. For the past 6 years, it has been a pleasure and a privilege to be one of the first to read these cutting-edge reviews, to work with authors who consistently put ego aside in the editorial process, and to rely on a pool of committed reviewers who volunteer their time to provide thoughtful and constructive critiques. I am enormously grateful to the JCPP editorial team for their support and encouragement. The people may be a-changin on the Annual Research Review editorial team, but I am confident the JCPP Annual Research Review will remain a go-to resource for readers wanting to learn about the best and most innovative research in child psychology and psychiatry.