Two twin studies at IBG are exploring the role of Executive Cognitive Functions (ECFs) as they relate to human development and behavior. ECFs are processes that control and regulate thought and action. They are involved with different cognitive abilities including planning ahead and problem solving, shifting between actions easily, initiating goal-directed behavior, and regulating attention in order to complete tasks. Our measures are taken from Miyake et al (2000), and some are modified for our sample. The testing process takes participants approximately 3 hours to complete.

Studies

ECF - LTS (Longitudinal Twin Sample):
The ECF-LTS is designed to examine the genetic and environmental contributions to executive cognitive functioning. The potential participation of all members of the LTS sample gives this study a unique longitudinal perspective on general and specific cognitive abilities. To find out more about the LTS sample and the Longitudinal Twin Study, please visit the LTS website.

The focus of this study is on the three best supported components of executive function: shifting of mental sets (shifting), updating information in working memory (updating), and inhibition of predominant responses (inhibition). Recently, Friedman et al. (2006) examined the relations of fluid intelligence, crystallized intelligence, and the Wechsler Adult Intelligence Scale IQ to inhibiting, shifting, and updating. Of these three executive functions, only updating was highly correlated with measures of IQ. The finding that these three ECF components are differentially related to intelligence measures suggests that current measures of IQ do not equally assess a wide range of executive control abilities.

ECF - CTS (Community Twin Sample):
This study is designed to investigate the relationship between ECF components and the development of behavioral disorders such as conduct disorder (CD), Attention Deficit Hyperactivity Disorder (ADHD), and comorbid substance use problems. ECF measures are assessed during a 5 year follow up interview with the CTS. These twins are enrolled in the Center for Antisocial Drug Dependence: Genetics (CADD). To learn more about this study, please visit the CADD website.

Preliminary analyses show strong evidence for the heritability of primary ECF constructs. Future research plans include the identification of ECF deficits that may partially explain the overlap between childhood disruptive disorders, and others that may help discriminate among them. 

Publications:

Friedman, N.P., Miyake, A., Corley, R.P., Young, S.E., DeFries, J.C., & Hewitt, J.K. (2006). Not all executive functions are related to intelligence.  Psychological Science, 17, 172-179. | pubmed abstract |

Friedman, N. P., Haberstick, B. C., Willcutt, E. G., Miyake, A., Young, S. E., Corley, R. P., & Hewitt, J. K. (submitted to Psychological Science) Attention Problems During Childhood Predict Poorer Executive Functions in Late Adolescence.

Friedman, N.P., Miyake, A., Young, S.E., DeFries, J.C., Corley1, R.P., & Hewitt, J. K. (submitted to Nature Neuroscience). The Unity and Diversity of Executive Functions are Genetic in Origin.

Sabella, S. A., Miyake, A., Friedman, N. P., Young, S. E., and Hewitt, J.K. (submitted to Cognition and Emotion). Not All Executive Functions Are Equally Related to Depression.  

Young, S. E, Friedman, N. P., Miyake, A., Willcutt, E. G., Corley, R. P., Haberstick, B. C., & Hewitt, J. K. (submitted to Journal of Abnormal Psychology). Behavioral Disinhibition: Its Structure and Relation to Response Inhibition across Adolescence.