Future Directions for research: What makes the Differential Susceptibility approach appealing to Psychopathology and Wellbeing researchers alike?
The Differential Susceptibility Theory (DST) has attracted a huge amount of research in recent years from researchers in the field of wellbeing and psychopathology for a variety of reasons. This essay will examine both the dominant diathesis-stress model and DST and highlight how the knowledge of DST can improve wellbeing and reduce psychopathology.
It has been widely demonstrated by decades of research that health and developmental disorders are more prevalent among people from high-risk families (Luthar, 2006; Boyce, 2007; Shonkoff, Boyce, & McEwen, 2009). Studies abound to demonstrate that childhood physical, emotional abuse and neglect impair development from lack of concentration to aggression, fighting, stealing, truanting and antisocial activities (Wayne, 1989). There is however a prominent variation in the physical health and psychological adjustment of both children and adults who experienced both high and low degrees of adversity (Luthar, 2006; Masten & Obradovic, 2006).
The dominant theory that accounts for the above phenomenon is the diathesis-stress/dual risk model, which emphasizes vulnerability to environment. It postulates that psychopathology develops as a result of an interaction between due to vulnerabilities/diatheses (temperamental, biological, and/or behavioural characteristics) in a particular person and environmental stress (Monroe & Simmons, 1991). Hence, an individual facing great environmental stress will not need to have many underlying vulnerabilities to develop psychopathology. The same outcome can be true for an individual with greater vulnerabilities but a minor stressful event (Ingram & Luxton, 2005).
On the other hand, DST emphasizes developmental plasticity- individual differences in neurobiological susceptibility to environmental factors (Belsky, 2005). Belsky (2005) postulates that plasticity functions in a for-better-and-for-worse manner: more “plastic” individuals experience more positive outcomes in positive environments as well as more negative outcomes in aversive environments.
DST has received support from many studies. Boyce et al.’s (1995) study on biological reactivity and environmental adversities as predictors of respiratory conditions in children aged between 3 and 5 yields a credible result. The study found that highly biologically reactive children who were exposed to childcare or home environments of high adversity experienced substantially higher illness than other children while highly biologically reactive children who experienced lower adversity conditions (better supportive childcare) experienced the lowest illness rates.
More recent studies come from Hankin et al.’s (2011) three different studies that investigated the 5-HTTLPR genotype in 1,874 children and adolescents (between 9- and 15-year-old) and how the degree of supportive or unsupportive parenting may influence their behaviours. Hankin et al. (2011) found that the ‘homozygous for the functional short allele of 5-HTTLPR were more responsive to parenting as environmental context in a “for better and worse” manner’, that genetically susceptible youth whose parents were unsupportive displayed low levels of positive affect while genetically susceptible youth who experienced supportive parenting displayed higher levels of positive affect.
There are a variety of reasons why researchers of well-being and psychopathology find DST appealing. The most significant difference between DST and the dominant diathesis-stress model is that the latter do not consider the effects of a positive environment. This is because it is of the view that there is no significant difference in how vulnerable or resilient groups respond to enriched supportive or environmental conditions (Belsky & Pluess, 2009). Consequently, many studies only focus on adversity and its absence (e.g., maltreatment vs. no maltreatment) and do not measure the complete range of environments. Neither do they consider the complete range of psychological/behavioural functioning (just maladjustment and its absence, e.g., depressed vs. not depressed).
In addition, DST may help researchers to elucidate the defining characteristics of resilience. Under the diathesis-stress model, children with particular attributes such as positive temperament and do not suffer expected detrimental effects of negative environments are defined as resilient (Cicchetti, 1993; Luthar, 2006). However, DST argues that these children could seem resilient because they are just not very “plastic” or malleable. If this is indeed true, these children would therefore be very unlikely to benefit from highly supportive rearing environments should they be provided with them (Belsky & Pluess, 2009b). As such, DST extends the diathesis-stress model by drawing focus on investigating how personal characteristics moderate the effects of positive environmental contexts on positive well-being.
One additional advantage of DST is that it offers a new advancement in the treatment of psychopathology. There is great potential in screening patients for intervention on the basis of neurobiological susceptibility (Ellis et al., 2011). DST predicts varying sizes of intervention effects across participants, depending on both the “plasticity” of individuals and the mode of intervention. Many experimental interventions on parenting and child care have confirmed the above prediction (e.g., Bakermans-Kranenburg, van IJzendoorn, Mesman, Alink, & Juffer, 2008; Cassidy et al., 2011). Furthermore, current evidence does not strongly support the case that some people are completely not susceptible to the positive effects of any intervention. As such, it would be better to understand neurobiological susceptibility as a continuous dimension rather than categorically (susceptible vs not susceptible). Caspi et al.’s (2003) G x E study showed that those homozygous for the short serotonin-transporter allele suffered most from stressful life events, those homozygous for the long allele suffered the least while heterozygotes (carrying one short and one long allele) fell in between. The above knowledge could help inform the design of treatment policies and programs tailored to the specific needs of people with differing “plasticity”.
Despite the exciting promise of DST, it is important to note that it is a relatively new theory in need of much future research to shed light on many areas. Owing to the length constraint of this essay, only a few notable areas will be discussed. Firstly, it is currently unclear how differential susceptibility is regulated by neurobiological (genotypic, endophenotypic, and behavioral) mechanisms (Ellis et al., 2011).
Future research on the relationships between the different levels of mechanisms would help to greatly shape programs and interventions to benefit patients of different “plasticity”.
Secondly, future research should focus on elucidating how for better and for worse processes unfold. For example, it could be possible that neurobiologically susceptible children are better at detecting and capitalizing on positive opportunities (e.g., taking advice from a teacher, forging strong friendships) to achieve positive outcomes in supportive environments. Such knowledge would once again help to shape intervention programs. For example, interventors can specifically highlight positive opportunities mentioned above to neurobiologically susceptible children from adverse environments that are recently provided with more positive environments.
In conclusion, this essay has explored the main features of DST and shown how understanding DST is crucial in understanding how to prevent psychopathology and improve wellbeing. Further studies, however, are required to bridge the existing gaps in this field.
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