Adverse childhood experiences (ACEs) are a general term for a large group of nonequivalent situations (Berman et al., 2022) that have the potential to traumatise a child (Sheridan et al., 2022; Wade et al., 2020; Malave et al., 2022; Lund et al., 2020). This risk factor is caused by a sensitive period of brain development, which is based on myelination, creation of synaptic connections and pruning (Haynes et al., 2025; Stiles and Jernigan, 2010; Uylings, 2006). The consequence of these processes will be the formation of the child’s connectome responsible for cognitive functions. In addition, these processes are due to the interaction of the child’s genetic apparatus, controlled by environmental factors (Gao et al., 2019). Dramatic environmental events during this period can disrupt optimal developmental pathways, leaving biological scars for life (Malave et al., 2022; Hakamata et al., 2022; Lund et al., 2022). One of the variants of traumatic experience is the abandonment of the child by a parent, leading to a history of institutionalisation. There is currently a consensus regarding the negative impact of institutionalisation on child development (Anthony et al., 2019; Bakermans-Kranenburg et al., 2003; Beckett et al., 2006), formed on the basis of an understanding of the consequences outlined in attachment theory (Bowlby, 1951; Bowlby, 1953), the concept of sensitive periods in early ontogenesis (Walasek et al., 2024) and an analysis of the consequences of stressful events on children (Gunnar and Quevedo, 2007; McLaughlin et al., 2019).

According to attachment theory, early relationships, primarily with the mother, not only determine the child’s current state of development, but also have significant consequences for his future cognitive outcomes, self-regulation, and ability to establish close relationships both during childhood and in adulthood (Beckett et al., 2006; Bowlby, 1953; Sroufe, 2005; Bernier et al., 2010). The concept of sensitive periods (Voss, 2013; Robson, 2002; Nelson and Gabard-Durnam, 2020; Knudsen, 2004) describes the influences that regulate the formation of a certain function in a certain period of time and determine the final result of the development of this function (Gunnar and Quevedo, 2007; Bailes et al., 2024). Both the data obtained from attachment research (Santaguida and Bergamasco, 2024) and the results of the study of children at the psychophysiological level indicate that the first 18 months of life are a highly sensitive period for the formation of a child’s interactions with the social world (Nelson, 2001).

Moreover, this is confirmed by studies where attempts to correct cognitive and psychosocial impairments in the child’s development, as well as problems with establishing secure attachment, were made at different periods of time, and it was shown that the maximum benefits of such interventions were found if they were implemented before the age of 18 months (Bakermans-Kranenburg et al., 2008; Wright and Edginton, 2016; Nelson et al., 2023).

Among the many consequences of institutionalisation, the deficit in the child’s cognitive functions is one of the most difficult to restore (Merz et al., 2013; Peñarrubia et al., 2020; Wade et al., 2019). First of all, a decrease in IQ is noted, which is sometimes explained by a change in brain volume (Mackes et al., 2020; Bick and Nelson, 2017). While foster care significantly restores both psycho emotional development (Forbes and Gallo, 2017; McCall et al., 2016; McCall et al., 2016; Garvin et al., 2012; Jaffari-Bimmel et al., 2006) and intelligence (Sánchez, 2015; Sonuga-Barke et al., 2017; Nelson et al., 2007; Van Ijzendoorn et al., 2005), for some aspects of cognitive development the negative consequences of institutional experience persist long after placement in a foster family (Bakermans-Kranenburg et al., 2008; Wade et al., 2019). Here we focus on executive functions which refers to a family of top-down mental processes needed, as Diamond describes, “to take time to think before acting; meeting unanticipated challenges; resisting temptations; and staying focused” (Diamond, 2013; Friedman and Miyake, 2017). In other words, using executive functions is effortful because they are involved in changing a patterned, habitual behaviour to a new one, that is appropriate to the new circumstances. Three core executive functions are usually distinguished: inhibitory control, working memory and cognitive flexibility (Friedman and Miyake, 2017; McKenna et al., 2017; Miyake et al., 2000). Given that the formation of executive functions is associated with the development of the prefrontal cortex, and is therefore long-term and non-linear (Friedman and Robbins, 2022; Anderson, 2002; Lieberman, 2020), this also indicates a large window open to both positive and negative environmental influences.

But what are these influencing factors? There is currently no clear understanding of what else, besides the fact of placing a child in an orphanage, influences the process of restoring executive functions after placing a child in a foster family. First of all, this difficulty is explained by the complexity of organising studies involving institutionalised children. Children have very different life histories prior to placement in an orphanage: both pre-institutionalisation experiences (Hawk et al., 2018), reasons for institutionalisation (Berman et al., 2022; The St. Petersburg–USA Orphanage Research Team, 2005), and post-institutional experiences (Vreeland et al., 2020) vary greatly. This suggests that each child can have a unique life-path influenced by many different factors, however their influence is reduced by the creation of a certain group of institutionalised children. And although all researchers came to the same conclusion that the longer the institutionalisation and the later the foster care intervention, the more pronounced the deficits in inhibitory control and working memory (Colvert et al., 2008; McDermott et al., 2013; Loman et al., 2013; Merz et al., 2013; Pollak et al., 2010; Desmarais et al., 2012), there is still confusion with age and the duration of placement in an institution (Julian, 2013). The challenge of studying the effects of institutional history also relates to individual child differences in vulnerability and resilience to early adversity, as well as in the quantity and quality of these experiences.

A meta-analysis of over 30,000 children with early adversity found that psychosocial deprivation, but not threat, was associated with significant declines in both inhibitory control and working memory (Johnson et al., 2021). Children adopted between 4 and 60 months of age with prior institutional experience continued to make more errors on an inhibition task nearly a decade later than their biological peers (Lewis et al., 2024). Another study compared children who were institutionalised immediately after birth with children who grew up in foster care. Both groups performed worse on inhibition and memory tasks 8 years later than a never institutionalised group, and the effect of foster care was found only after controlling for prenatal factors (Bos et al., 2009). Stinson et al. (2024) assessed the state of inhibitory control in children at 8 years old, after they were adopted from an orphanage at age 3, finding that differences in executive functions persisted.

There is evidence that the long-term consequences of institutionalisation are more pronounced the earlier the child enters the orphanage. Moreover, there is an opinion that the risk of increasing social and psychological problems is not determined by gradual changes, but is abrupt, sharply increasing in a certain time range (Julian, 2013). The age at which significant changes occur is determined by the severity of the conditions of institutionalisation. And such a jump may occur at 6 months for Romanian children studied within the Bucharest project (Rutter, 2006) and 18 months for Russian children (Naumova et al., 2019). The presence of such a boundary effect was also noted in the study, which noted that staying in a blood family during the first 9 months after birth reduced the severity of the consequences of further stay in an orphanage (Hawk et al., 2018).

The hypothesis to be tested in this study is that there is a critical period for the formation of optimum working memory and inhibitory control within the first 18 months of a child’s life. This suggests that children who were placed in an institution during this period and then despite being placed in a substitute family will not achieve the parameters of working memory and inhibitory control that will be found in children who end up in an institution after this period. We make this assumption based on the relationship between these executive functions, the development of the prefrontal cortex, and the importance of the first years of life in the functional development of the prefrontal cortex (Jeong et al., 2024; Fox et al., 2010).

The aim of the research reported here was to explore the impact of early institutionalisation history on the formation of inhibitory control and working memory in children, and to test the speculative hypothesis if there is a critical period in the development of these functions which is limited to the first 18 months of the child’s life. This hypothesis was based on the dependence of various components of the formation of executive functions on the development of neural networks generated by the prefrontal cortex (Hanson et al., 2013; Cheng et al., 2021; Teicher et al., 2016). Interest in executive functions is related to their resource component. It is understood that executive functions are responsible for activity associated with behavioural change, i.e., numerous types of activity that allow a child traumatised in early childhood to restore their potential in the cognitive sphere. We hypothesise that a decrease in the specialisation of neural networks during stress in early ontogenesis (Malave et al., 2022; Hambrick et al., 2019; Hostinar et al., 2018) reduces the potential for recovery of executive functions at a later age.

The development of executive functions is usually associated with the so-called “expectable environment” (Nelson and Gabard-Durnam, 2020; Fox et al., 2010), which is rich in sensory and cognitive stimulation. It has been established that executive functions are formed in preschool childhood (Best et al., 2009; Rueda et al., 2016), with working memory developing significantly already in the first 12 months of life (Buss et al., 2018) and by the age of six, reached a basic modular structure (Gathercole et al., 2004), while inhibitory control much more slowly (Nikolaeva et al., 2020), nevertheless is observed by age of seven the relative level of productivity of this component (Best et al., 2009; Rueda et al., 2016). However, when the environment does not match the expected experience, the development trajectories of the EF may vary (Sonuga-Barke et al., 2017; Vasilyeva et al., 2017).

We first compared outcomes of measures inhibition and working memory tasks between the never institutionalised group and the ever-institutionalised group living in substitute care at the time of the study. The ever-institutionalised group had the lowest scores on most outcomes, including number of errors and number of stimuli remembered. These findings are consistent with previous studies of working memory (Bos et al., 2009) and inhibitory control (McDermott et al., 2013; Loman et al., 2013) in children with institutional history. Analysing the role of substitute care, we found that the protective effect of family was significant for the working memory task, eliminating any differences between the ever and never institutionalised groups. However, the significant differences in performance on the inhibition task remained. A previous experiment compared the outcomes of never institutionalised children with two groups of children who entered early institutional care (in the first 2–3 months of life), with the only difference being that some remained in institutional care and the others were immediately placed in foster care (McDermott et al., 2013). It was shown that after 8 years, children from both foster care and institutional care were equally worse on the inhibition task compared with a control group that had never been institutionalised. In other words, it seems that the factor of early placement in an institution, even for a short time, was more influential than the early intervention of foster families. It appears the rule “the earlier the better” (Zeanah et al., 2011) (implying fostering) helps, but does not solve, all the developmental challenges of children placed in institutions.

Then, in accordance with the objectives of this study, the ever-institutionalised children were divided into two groups: early and late institutionalised. The empirical basis for the age cutoff was previous research showing that children institutionalised after 18 months have better cognitive development outcomes after institutional intervention (Hawk et al., 2018), in another study this cutoff was lowered to 9 months (Julian, 2013), and in the case of severe deprivation observed in Romanian institutionalised children—to 6 months (Rutter, 2006). Since this may mean the most sensitive age cutoff for working memory and inhibitory control varies somewhere within the first 2 years of life, we tested different cutoffs in 6-month increments within 24 months. Thus, we compared groups of those institutionalised before 6 months with those after this age, then those institutionalised before 12 months with those after, and so on.

Although the analysis of the results depending on the age of placement only within the ever-institutionalised group did not show significant differences, they were found when comparing the early institutionalised groups with the never institutionalised group. For the performance of working memory tasks, the most sensitive age cutoff was 18 months, while for inhibition tasks it was 12 months. This means that the never institutionalised group had significantly higher scores on the working memory key test tasks compared only with those children who were institutionalised before 18 months, whereas there was little difference in scores with the group institutionalised after this age.

For the inhibition scores, the age cutoff dropped to 12 months, moreover differences appear in the second part of the go/no-go series. This can indicate greater vulnerability and instability of inhibitory control due to the lack of resources to support more complex cognitive activity that is consistent with the literature on the disruption of neural networks in children exposed to ACE’s in the early period of development (Nelson et al., 2023). This is particularly curious given that the early and late institutionalised groups did not differ in gender, caregiver characteristics, or length of institutionalisation, but the early institutionalised group received more substitute care, and in the comparison group at the 12-month cutoff, this difference in duration of substitute care was statistically significant.

One of the results of the study was the discovery of vulnerability to stress in the early ontogenesis of the retrieval-based learning mechanism in working memory, which is responsible for resisting the mechanism of proactive interference (Anderson et al., 2000). This mechanism allows the retention of information, despite the emergence of new information (Karpicke, 2012). In the current study, working memory is assessed in three attempts, each of which presents the same set of stimuli, but in a different sequence. The child is required to select a stimulus that was not selected in the current attempt, but could have been selected in the previous attempt. When the child makes the first attempt—the first reproduction, they often remember many stimuli. Therefore, when they reproduce them for the second time, they encounter proactive interference, when the previous information interferes with the reproduction of the next one (Anderson et al., 2000). Most normally developing children after 5 years of age try to find a method to resist such a mixture of stimuli and strive to develop a strategy for independently memorising information in the third reproduction (Forest and Amso, 2023). But institutionalised children, probably, are not ready to resist this mechanism of projective interference, and therefore the last reproduction has a minimum number of elements.

The suppression of irrelevant information is a function of the prefrontal cortex (PFC) (Anderson and Hulbert, 2021). The specificity of its formation is that throughout a child’s development it is involved in the process of developmental management (Andersen, 2003) beginning in the early postnatal period. Myelination in the PFC differs from that occurring in other brain regions in the postnatal period due to the longer presence of premyelinating oligodendrocytes (remaining from the prenatal period). They are more vulnerable to perinatal damage than mature oligodendrocytes and predominate in the frontal lobe areas at birth (Back et al., 2001), which clearly makes the early white matter of the frontal lobe susceptible to injury. It is worth emphasising the important role of early migration of prefrontal neurons to the cortex: this allows them to participate in the organisation of early brain activity (Collin and van den Heuvel, 2013), but at the same time leads to a unique vulnerability of the frontal white matter to early injury (Hodel, 2018). Modern non-invasive methods of studying infants convincingly demonstrate that it is in the first years of life that extensive structural development of the prefrontal cortex occurs, and it plays a unique role in connecting other brain structures to the general network (Buss et al., 2018; Massera et al., 2023; Wade et al., 2022; Kolb et al., 2012).

The results of this study show that the outcomes of working memory and inhibitory control of children who were placed in an orphanage after 18 months, but later found themselves in a substitute family, are comparable to the outcomes of children without the experience of institutionalisation. However, such a correspondence is not observed in children who were placed in an orphanage before 18 months. In addition, early institutionalised children ended up spending more time in the substitute family than late institutionalised children. However, the beneficial effect of family placement on cognitive functions was more successful in late institutionalised children. The “earlier the better” rule probably does not apply to the sample of this study as well, since some of the early institutionalised children were placed to substitute families 2–3 months after entering an institution, but this did not affect their results. Could these data serve as a prerequisite for the presence of a critical period in the formation of working memory and inhibitory control?

The term “critical period” comes from animal models [e.g., (Hubel and Wiesel, 1970)], is commonly used to describe sensory systems [e.g., (Kral et al., 2019; Maurer et al., 2007)], and explains how experience affects the brain in ways that permanently alter performance. In humans, the term “sensitive periods” is more commonly used to reflect the brain’s characteristic neuroplasticity and high sensitivity to the environment throughout life (Zeanah et al., 2011; Stamps and Luttbeg, 2022; Frankenhuis and Walasek, 2020). We propose to consider the concept of “critical” period in relation to the development of working memory and inhibitory control in the first 18 months of life, underlining the neurobiological nature of the phenomenon (Larsen and Luna, 2018; Uylings, 2006). It has been suggested the plastic capabilities of the brain are provided by the absence of myelination. Gradual myelination leads to a narrowing of these capabilities (Uylings, 2006). A recent intriguing study showed that in 29 institutionalised infants, some methylated genes were correlated with the length of stay in an orphanage, including a gene required for the organisation of myelinated axons during brain development (Naumova et al., 2019). In other words, by using the term “critical” period, we want to emphasise that after being institutionalised, some children adjust worse than others to the new conditions (Ellis et al., 2009), and, different brain systems within a person may adjust to new conditions at different rates (Zeanah et al., 2011).

We would like to acknowledge several important limitations of this study that should be taken into account in the interpretation. The first and most important limitation is related to the wide age range of the study sample. Despite constant age control in statistical analyses, the results remain vulnerable to proof. In addition, the lack of information on the prenatal period of children’s development and the quality of parent–child relationships with their biological parents in the first 18 months of life also limits the possibilities of interpretation. Finally, the present study is cross-sectional, which precludes claims about causal mechanisms for the observed results. Further development of the concept of a critical period for the development of executive functioning components requires further longitudinal studies with strict controls for the life trajectory of the child exposed to adversity.

In conclusion, when looking for a common denominator that may help explain the impact of family deprivation during early life critical periods in brain development on infants placed in institutions the lack of, primarily maternal, nurturing care, is posited here as a major candidate for the source of such deprivation. Maternal tactile affection, as mediated by gentle caressing touch, provides an optimal stimulus for a class of thermo-mechanosensitive unmyelinated afferents innervating the skin of the body, called c-tactile afferents (CT) (McGlone et al., 2014). Animal models of juvenile social isolation result in myelination changes that mimic conditions related to neurodevelopmental disorders, with prolonged social isolation, and therefore tactile deprivation, inducing hypomyelination in the PFC, partially explaining the long-term consequences of early childhood experiences on the development of working memory and inhibitory control reported in this paper (Liu et al., 2012).