We tested the hypothesis that placement of institutionalized children into foster care at ages ranging between 7 and 31 months would be associated with a specific profile of the resting EEG in the FCG at 42 months of age. Relative to the continually institutionalized children, the FCG children were hypothesized to show low levels of slow frequency power and increased levels of higher frequency power, as well as lower levels of short-distance EEG coherence. We tested this hypothesis by comparing the foster care and institutionalized groups at the 42 month assessment. We also tested an accompanying hypothesis that earlier placement into foster care would have a greater impact on EEG power and coherence than foster care that was initiated at a later age. This second hypothesis was initially tested by computing correlations between foster care placement age and EEG coherence measures, as well as a basic group approach which involved splitting the FCG into groups of children who had been placed before or after 24 months of age. A subsequent approach involved creating subgroups within the foster care group such that the children in these subgroups had entered foster care at different ages but had received, on average, a similar duration of intervention.
Considering EEG power, the initial analysis comparing the groups at 42 months of age did not reveal main effects of the foster care intervention. One interpretation of this lack of findings is that the intervention was essentially unsuccessful in changing EEG band power in the foster care group relative to the institutional group. However, it is also possible that the wide variability in age at foster care placement obscured changes in the EEG which were associated with age at placement. Given that the age at foster care placement ranged between 7 and 31 months of age, it could be that effects on EEG power were only apparent for the small number of children placed into foster care at the earliest ages in the study. Subsequent analyses indeed suggested a relation between age at placement into foster care and certain EEG power measures at the 42-month assessment. For instance, age at placement was negatively correlated with both absolute and relative alpha power within the FCG. Visual inspection of the scatterplots showing the relation between these variables suggests that the negative correlations between placement age and EEG alpha power were driven by a group of children who had entered foster care at the earliest ages (between 7 and 15 months of age). Group analyses which split the foster care group into two groups (placed before 24 months of age and placed after 24 months of age) also suggested that children who entered foster care earlier had higher alpha power at 42 months of age than the institutionalized group.
The above findings concerning EEG power are subject to at least three explanations, each of which raises a number of further questions relating to the confounding of age at foster care placement and duration of foster care intervention in the 42 month data. One interpretation is that the foster care intervention was unsuccessful at changing EEG power in the FCG, and that the group of early-placed children which appears to be driving the correlational findings is too small to warrant strong conclusions about the effect of foster care on the EEG. We do not believe that such an interpretation is warranted. A second interpretation would be that the foster care intervention was successful in changing the EEG only for children who began to receive the intervention at the earliest ages of the study, and that this change for these children was due to the intervention occurring within a sensitive period for EEG development. From this perspective, the design of the study did not include enough children placed earlier (e.g., in the first year of life) for overall group differences to be detected in EEG power at 42 months. A third, opposing interpretation of the correlational findings states that the profile of EEG power observed at 42 months in the group of children entering foster care at the earliest ages is primarily due to the longer duration of intervention for these children, rather than earlier placement into foster care. This interpretation would also suggest that the overall mean duration of intervention was too short to reveal group differences between the IG and FCG on band power at 42 months, and further, that IG/FCG group differences would emerge at assessment ages later than 42 months.
Given the confound in the current study between age at placement and the duration of foster care at the 42-month assessment, it is problematic to chose between the second or third interpretations presented above on the basis of the correlations between age at foster care placement and the EEG variables. We attempted to address this issue by creating subgroups of children of children in the foster care group who had received similar mean durations of intervention, but who had been placed either at younger (mean 13 months) or older (mean 27 months) ages. This analytic approach involved assessing the early-placed group at the 30-month age point and the late-placed group at the 42-month age point. This enabled a number of key comparisons to be made. The early-placed FC subgroup was compared on the 30-month measures with the subgroup of IG children who entered the study at similar (early) ages, and the late-placed FC subgroup was compared on the 42-month measures with the subgroup of IG children who entered the study at later ages. The early-placed FC subgroup at 30 months of age was also compared with the late-placed FC subgroup at 42 months of age. However, while the latter comparison is appropriate for standardized measures, developmental changes in the EEG introduce some problems into the interpretation of this comparison. Finally, we compared the early-placed FC subgroup and the appropriate IG comparison subgroup at 42 months of age, at which time the FC children had received between 24 and 36 months of foster care.
The subgroup analyses for EEG band power utilized the three power measures for which the 42-month correlations with age at placement were of the strongest magnitude: Absolute and relative alpha power, and relative beta power. At the 30-month assessment, after a mean duration of 18 months in foster care, the early-placed foster care subgroup did not differ on these EEG power measures from the group of IG children who entered the study at similar ages. The early-placed FC subgroup also did not differ from the late-placed FC subgroup on the three measures of EEG band power. In the third set of comparisons, the early-placed FC subgroup did differ from the appropriate IG comparison group on relative alpha power at 42 months of age. While the small sizes of the subgroups at the 42-month assessment may limit the degree of inference possible from this finding, it does suggest that effects on alpha power were not apparent for children in the FCG after 12–24 months of intervention, regardless of whether they were placed into foster care at earlier (<18.5 months) or later (>18.5) ages. Instead, differences between the IG and FCG began to emerge in the children placed at the earliest ages after the longest durations of intervention (24–36 months). This is consistent with the patterns evident from the scatterplots in for relative alpha power, where the correlation appears to be driven by the small group of children placed at the earliest ages. However, this finding still leaves open the question of whether the key aspect is whether children were placed into foster care at earlier ages, or whether 24–36 months of foster care is needed in order to see group differences emerge in relative alpha power, regardless of age at placement.
As seen above, effects of the intervention on EEG band power primarily concerned changes in relative alpha power for the children placed at the earliest ages in the study, who also received the longest durations of intervention. The coherence measures presented a slightly different picture in terms of the effect of the foster care intervention on the resting EEG. As for EEG power, the initial between-group analyses for coherence did not show clear overall effects of the foster care intervention. However, a weak interaction between group and hemisphere emerged which suggested that the intervention was associated with overall lower right-hemisphere coherence in the FCG compared with the IG. Since we did not have specific hypotheses concerning intervention effects on hemispheric asymmetries in coherence, this finding is difficult to interpret. However, prior developmental work has suggested that better performance on cognitive tasks has been associated with decreased right-hemisphere coherence, although this work was primarily with younger infants (Bell, 2001
; Bell & Fox, 1997
). In addition, lower coherence in the right hemisphere compared with the left has also been observed in typical development (Barry, Clarke, McCarthy, & Selikowitz, 2005
; John et al., 1980
While the overall FCG-IG comparison did not yield clear main effects for coherence, the correlational analyses revealed significant, negative relations between age at foster care placement and specific coherence measures at 42 months. Analyses using a median split approach also suggested that FCG children placed before 24 months of age differed from the IG at 42 months, while the FCG children placed after 24 months of age did not. The measures which showed this pattern were primarily those which indexed coherence across relatively short inter-electrode distances (frontal-central and frontal-temporal) for the alpha and beta bands. Coherence between pairs of electrodes which were more spatially separated (frontal-parietal and frontal-occipital) was not related to age at foster care placement. In addition, coherence across both short- and long-distance derivations for the theta band did not show any relation with age at placement. The focus of the coherence analyses was therefore on short-distance coherence, primarily in the alpha band.
The analysis strategy of examining subgroups that was used to separate the effects of placement age and duration intervention for EEG power was also used for the analyses of EEG coherence. The primary finding for coherence was that at the 30-month assessment, frontal-temporal alpha coherence was significantly lower in the early-placed FC subgroup than the appropriate comparison subgroup of the IG. The later-placed FC subgroup did not show a similar pattern of low frontal-temporal coherence. This suggests that effects of the foster care intervention on EEG alpha coherence at 30 months of age were apparent for a specific short-distance electrode combination (frontal-temporal) for children placed into foster care before 18 months of age. The same effects of early placement while holding duration of intervention constant were not as apparent for the other coherence measures, specifically alpha and beta coherence between frontal and central electrode sites. However, it should also be noted that the early-placed FC subgroup at 30 months had lower frontal-temporal and frontal-central alpha coherence compared with the late-placed FC subgroup at 42 months. While it is somewhat problematic to compare across different age points because of maturational factors, these findings support a general interpretation that earlier ages at foster care placement were associated with lower short-distance alpha coherence at later assessments.
When the early-placed FC subgroup was compared with the appropriate IG subgroup at the 42-month assessment, all three coherence measures (frontal-central alpha and beta coherence as well as frontal-temporal alpha coherence) showed group differences. This suggests that intervention effects on aspects of EEG coherence emerged consistently for the earliest-placed children in the foster care group after the longest possible durations of intervention (24–36 months of foster care).
For a number of our EEG variables, the lack of an EEG assessment after 42 months of age precludes strong inferences about the effects of earlier placement versus longer durations of intervention. Despite this constraint, our theoretical bias leads us to favor an interpretation that earlier age at placement into foster care was responsible for the correlations of the EEG measures with age at foster care placement, despite the confound of this variable with duration of intervention. Such an interpretation is consistent with work on post-institutionalized, internationally-adopted children in which earlier age at adoption was associated with improved cognitive outcomes compared with adoption at later ages (MacLean, 2003
; Rutter, 2006
). While transitions to a more favorable caregiving environment are almost always associated with improvement in various domains of functioning (Clarke & Clarke, 2000
), there is also evidence suggesting that plasticity in a number of behavioral and neurobiological systems may indeed be greater at earlier ages (Nelson et al., 2007
; O'Connor, 2003
In terms of limitations, there are a number of questions that could be raised about the current findings. One question concerns the observation that contrary to one of our initial hypotheses, the foster care intervention did not appear to change theta (low-frequency) EEG power. In comparing the entire institutionalized sample with the community comparison sample at the baseline assessment (i.e., prior to randomization),Marshall et al. (2004)
reported an EEG profile in the institutional group characterized by an excess of theta power combined with a reduction in higher frequency (alpha and beta) power. This EEG profile has been associated with cognitive delays, learning disabilities and attentional problems in a variety of samples (mostly with older children) and was interpreted byMarshall et al. (2004)
as signifying two possible deficits: Cortical hypoarousal (from the lack of higher-frequency power) or a delay in the development of the EEG as indicated by the excess of low-frequency theta power, which is expected to decrease with age. Given the strength of findings concerning an excess of theta power in the EEG profile of the institutionalized children at baseline, it is somewhat surprising to see intervention effects mostly occurring in the alpha band and not also the theta band.
Another particularly important question concerns the functional significance of the EEG changes that were observed in the current analyses. In terms of alpha power, the main finding was that the children placed into foster care at the earliest ages showed increased levels of power at the 42 month assessment, relative to children in the institutional group. Our perspective on this finding is that the increase in alpha power in the FCG represents a partial remediation of the deficits in this measure that were present at the baseline assessment. When viewed in the context of the models presented byMarshall et al. (2004)
, this remediation may represent catch-up in the development of the EEG in the foster care children placed at the earliest ages in the study. In terms of coherence, the current findings are consistent with work byMundy et al. (2003)
, who showed that decreased short-distance EEG coherence in infancy was predictive of improved language outcomes, as well as research relating increased coherence to cognitive delays in children (Gasser et al., 1988
; Marosi et al., 1995
A final question concerned how the changes in EEG power and coherence relate to changes in other measures in the BEIP, particularly assessments of cognitive status. As suggested in the introduction to this paper, one theoretically favorable model states that changes in neurobiological measures may be expected to mediate changes in behavioral or psychological measures that are seen in response to a given intervention. When the children placed in foster care were assessed at 42 months, we did observe correlations between specific EEG band power variables and scores on particular tests of intellectual functioning, namely the Reynell language scales and the developmental quotient derived from the Bayley scales. We also found that specific EEG measures and the scores on the cognitive assessments tended to correlate with the age at placement in foster care for the FCG. These intercorrelations, along with the other evidence presented here and elsewhere (Nelson et al., 2007
) suggest that the children placed in foster care at earlier ages show concurrent gains in both cognitive functioning and the development of certain aspects of the EEG signal (e.g., an increase in alpha power). However, analyses using partial correlations and multiple regression did not find particular evidence suggesting that the EEG variables were mediating the changes in DQ or language abilities. It is possible that our sample size was too small to detect such effects, but the lack of mediation also illustrates the often complex and sometimes counterintuitive relations between measures of physiological functioning and measures tapping complex psychological constructs. The nature and importance of these cross-domain relations has been the subject of much debate both within the domain of developmental psychopathology (e.g., Cichetti & Curtis, 2006
; Pollak, 2005
) and in psychology more generally (e.g., Kagan, 2006
Additional limitations of the current analyses should be pointed out. Although we found particular effects of age at placement, it should be noted that children were not randomized on age at foster care placement. This leaves open the possibility that children placed earlier and later into foster care may have differed on certain preexisting characteristics. However, analyses of these subgroups at baseline did not reveal preexisting differences on the EEG variables that were used as later outcomes. Perhaps more importantly, the sample sizes at 42 months of age were relatively small given the (reasonable) rate of attrition and noncompliance with the EEG procedures. The small sample sizes were particularly evident in the comparison of the early- and late-placed foster care subgroups and the comparison subgroups of institutionalized children, so our conclusions about age at placement may be tempered by issues of statistical power as well as the possibility of a Type I error. One final point concerns the lack of strength of the intervention effects. It should be noted that the intent-to-treat analysis adopted in the current paper represents a conservative approach towards the assessment of the foster care intervention. Since a significant number of the institutionalized children were no longer living in institutions at the 42-month assessment, the foster care intervention is essentially being compared to the natural course of institutionalization over the course of the 3 years of the study. This three years turned out to be a fairly rapid period of social change in Romania, and the natural course of institutionalization for young children over those three years often did not involve staying in an institution, and for many children involved a placement into an alternative, family environment. This could be one of the contributing factors why we did not observe clear overall effects of the foster care intervention on the EEG at the 42-month assessment. Finally, the EEG measures used in the current study were non-specific, and were not collected during an active task. The low-density electrode array utilized does not lend itself to particular conclusions about particular brain systems that were impacted by the foster care intervention. Instead, our conclusions about brain function are limited to fairly general EEG profiles that have been associated with global cognitive functioning rather than more specific behavioral or psychological constructs.
In summary, we believe that we have found evidence for foster care being associated with neurophysiological changes in the central nervous system in previously institutionalized children, with the extent of these changes being partly dependent on age at placement into foster care. In this sense, the current study provides a novel and unique perspective on brain-behavior relations in early preventative interventions.