Effects of Environmental Enrichment at Ages 3–5 Years on Schizotypal Personality and Antisocial Behavior at Ages 17 and 23 Years

Nutritional, educational, and physical exercise enrichment at ages 3–5 years was associated with lower scores for schizotypal personality and antisocial behavior 14–20 years later, compared with usual community conditions. The beneficial effects associated with the intervention tended to be greater for children who were malnourished at age 3, particularly with respect to outcomes for schizotypal personality at ages 17 and 23 and conduct disorder at age 17. The fact that the prevention program was associated with effects for two different forms of psychopathology that were assessed by using two different types of outcome measures (self-report and objective measures) at two follow-up points extending over 20 years indicates the robustness of the effects. The results cannot be attributed to pre-enrichment group differences in temperament, cognitive ability, nutritional status, autonomic reactivity, or demographic variables. To our knowledge, this program constituted the first attempt at primary prevention of schizotypal personality. The findings are consistent with an increasing body of knowledge that implicates an enriched, stimulating environment in beneficial psychological and behavioral outcomes (48–50) and have potential implications for the prevention of crime and schizotypal personality, particularly in populations at risk for malnutrition.

One limitation of this study was the inability to determine which component(s) of the intervention (nutrition, exercise, or education) accounted for the later beneficial effects. Nevertheless, children who were malnourished at age 3 years were significantly more likely to benefit from the program at age 17 years and at age 23 years, compared with children who were not malnourished at age 3 years. Scores at age 17 years for subjects who were malnourished at age 3 years were 53.0% lower for conduct disorder, 41% lower for motor excess, 43.2% lower for psychotic behavior, and 32.4% lower for cognitive disorganization, compared with the scores at age 17 years for subjects who were not malnourished. Scores at age 23 years for subjects who were malnourished at age 3 years were 23.0% lower for total schizotypy and 31.6% lower for interpersonal deficits, compared with the scores at age 23 for subjects who were not malnourished at age 3 years. Nutritional deficits have been linked to both schizophrenia and schizoid personality disorder (24, 25, 51) and also to antisocial behavior (23). In particular, a recent double-blind, placebo-controlled, randomized trial has shown the effectiveness of nutritional supplements in reducing antisocial and violent behavior in prisoners (52). It is conceivable that aspects of the nutritional intervention such as fish supplementation could benefit brain function because omega-3 fatty acids have been reported by some to have beneficial effects on both schizophrenia (53–55) and externalizing behavior problems (56–59). In contrast to nutrition, psychophysiological status was not a significant moderator. Taken together with the findings of other successful early prevention programs that have manipulated nutrition (28), the current findings suggest, but do not prove, that the nutrition component of the enrichment program may account for some of the benefits.

Alternative hypotheses must also be considered. For example, the prevention program included 2.5 hours each day devoted to physical exercise and outdoor play, and it is conceivable that exercise by itself could account for a significant proportion of the observed effects. Exercise in animals is known to increase mRNA in the hippocampus and to have other beneficial effects on brain structure and function (60). Furthermore, the effect of environmental enrichment in producing neurogenesis in mice has been attributed to the sole effects of running, independent of other components of enrichment such as maze training (13). As such, physical exercise could both benefit brain functioning and protect individuals from developing schizotypal personality and antisocial behavior, both of which have been linked to structural and functional brain deficits (15–18, 61). Another hypothesis that needs to be considered is that the increased social interaction with positive, educated preschool teachers in the experimental enrichment program may in part account for the beneficial effects of the prevention program. Alternatively, it may be unreasonable to focus on any single component of the intervention. Instead, the multimodal nature of the prevention program, which incorporated social and cognitive components along with nutrition and exercise components, may have facilitated interactions between these components that critically affected later development. Follow-up studies that both replicate the multimodal enrichment strategy as well as tease apart the individual components could usefully address this issue.

One prior study has shown that educational enrichment has long-term effects in reducing antisocial and criminal behavior (28). Thus, it is possible that the educational component of the prevention program could have accounted for the long-term reduction in criminal offending. In the previous study, the participants in the educational enrichment program were children from poor homes, and it has been argued that enrichment may particularly benefit children affected by social adversity (62). No support was found for this argument in the current study, as social adversity did not moderate the effects of the enrichment program. Instead, children affected specifically by malnutrition were more likely to benefit from the enrichment. Consequently, nutritional status in particular, rather than social adversity in general, may be a particular factor to consider in future prevention programs intended to address schizotypy and antisocial behavior.

The fact that the prevention program was associated with lower levels of schizotypal personality in late adolescence and in early adulthood in the malnourished group may help intervention efforts aimed at preventing or delaying the onset of schizophrenia (2, 3). Schizotypal personality is a disorder that shares with schizophrenia a range of neurocognitive, neurophysiological, genetic, psychophysiological, and symptom characteristics (21, 63) and has much in common with the prodromal, prepsychotic stage of schizophrenia. If features of schizotypal personality can be attenuated by early environmental enrichment, it is possible that the development of the prodromal features of schizophrenia may also be reduced, in turn delaying or preventing the onset of schizophrenia itself (3, 64). The fact that one of the strongest effect sizes in this study was obtained for interpersonal deficits in the malnourished group at age 23 years (d=0.56) is of particular relevance, as these negative schizotypal traits feature strongly in the schizophrenia prodrome, as described in DSM-IV (65, 66). Despite these findings, it must be reemphasized that this study showed only lower levels of schizotypal personality in a nonselected group, and it remains to be seen whether such prevention efforts can achieve results of clinical significance in relation to schizophrenia itself, as have been achieved with secondary prevention efforts (65).

Although the prevention program was associated with a significantly lower conduct disorder score for subjects at age 17 (d=0.44), we caution that the effect size for subjects at age 23 years was smaller (d=0.26 for self-reported criminal offending; d=0.22 for criminal offending according to court records). In this study, the level of criminal offending at age 23 years according to self-reports was significantly lower in the enrichment group than in the control group (p<0.05). The level of criminal offending by age 23 years according to court records was 63.6% lower for the enrichment group than for the control group (which equals or exceeds effects found in short-term intervention studies [67]), but the difference failed to reach statistical significance (p=0.07). On the other hand, base rates for criminal offending according to court records were lower than those for self-reported offending, and the possibility that floor effects precluded statistical significance must also be considered. A recent review of prevention programs for crime showed that even the very few model prevention programs that have shown success rarely if ever show effects beyond the teenage years (67). The large majority of prevention programs do not start early in life, when the pathway to antisocial behavior is believed to begin (68, 69). On the other hand, it may be questioned why any effect 20 years later was associated with a prevention program that lasted only 2 years early in life. Although stronger long-term effects may be expected of a longer environmental enrichment program, it has been found that early withdrawal from an environmental enrichment doubles the number of new hippocampal cells in mice, compared to more sustained enrichment (70). Thus, some long-term beneficial effect of the 2-year enrichment is not inconceivable. Future studies may assess whether a booster enrichment session later in childhood leads to stronger effect sizes for criminal behavior in adulthood.

In conclusion, these initial findings suggest that early environmental enrichment is associated with lower levels of antisocial behavior and schizotypal personality in adulthood and that benefits are greatest for children with poor nutrition. We caution that findings from a country that was still developing when the prevention program was conducted cannot be directly extrapolated to more developed countries such as the United States. Nevertheless, the findings may be particularly relevant to poor rural areas of the United States, such as the Mississippi delta region, and also to U.S. inner cites, where rates of both malnutrition and behavioral problems in children are relatively high (71, 72).

Received May 14, 2002; revisions received Nov. 25, 2002, and Jan. 22, 2003; accepted Feb. 6, 2003. From the Department of Psychology, University of Southern California; the Mauritius Child Health Project, Quatre Bornes, Mauritius; the School of Nursing, University of California, Los Angeles; and the Department of Psychology, University of York, Heslington, York, U.K. Address reprint requests to Dr. Raine, Department of Psychology, University of Southern California, Los Angeles, CA 90089-1061; [email protected] (e-mail). Supported by NIMH Independent Scientist Award MH-01114-01, NIMH grant MH-46435-02, and a Scholar-in-Residence award from the Borchard Foundation to Dr. Raine; grants from the United Kingdom Medical Research Council, the Leverhulme Trust, and the Mental Health Foundation of the United Kingdom to Dr. Venables; NIMH Research Scientist Award MH-00619-08 to Dr. Mednick; and a grant from the Ministry of Health of the Government of Mauritius. The authors thank Marie-Clare Calambay, Meena Calinghen, Athene Chiriaca, Cyril Dalais, and Devi Jaganathen for help in data collection and scoring.