William G Iacono
In most of my research, family, adoptive, and twin study designs are used to investigate the development and etiology of common mental disorders, including substance use, antisocial, and major depressive disorders. This work is carried out through the Minnesota Center for Twin and Family Research that I co-direct with Matt McGue, and include the Minnesota Twin Family Study (MTFS) and the and the Sibling Interaction and Behavior Study SIBS.
Teenage drinking and drug use constitute a major public health problem, but it is unclear to what degree the poor long-term outcomes often seen for teen substance abusers are due to the effects of the drugs as opposed to factors that influenced their use the drugs in the first place. A particularly important concern focuses on how substance use affects brain development in youth. Together with collaborators Stephen Malone in the Psychology Department and Kathleen Thomas in the Institute for Child Development, my work examines neurocognitive and mental health outcomes for twins who were first studied in pre-adolescence and are now adults. It is known that adolescents who misuse alcohol and illicit drugs show poor psychological adjustment as adults, and they also show signs of brain impairment on neuropsychological tasks and in MRI and EEG studies. However, it is also the case that those at risk for becoming drug abusers in adolescence show some of these same brain characteristics before exposure to drugs and alcohol. Hence, it is not known to what extent the neurocognitive deviations seen in adolescents who misuse substances are the cause or consequence of their drug use.
One way to examine the likelihood that substance abuse causes neurocognitive deficits is to study twins who differ in their drug use. Twins are matched for shared environmental circumstance (e.g., like being reared by an alcohol dependent parent in a chaotic environment), and so-called identical or monozygotic (MZ) twins are matched for genetic risk likely to influence both their substance use and their brain development. In such a study, the lesser substance using twin becomes the control for the effects of substance abuse seen in the heavier using co-twin. In the evaluation of the possible neurotoxic effects of substance abuse, the lesser substance using twin’s brain provides a glimpse of what the heavier using twin’s brain should be like had the heavy user not misused substances. If the two twins’ within a pair are neurocognitively similar as adults despite their different histories of substance abuse, pre-existing risk factors, and not substance misuse, account for any observed neurological anomalies associated with substance abuse. To the extent that the heavier using twin’s brain is different from the lesser using co-twin’s, the observed brain deviation can be attributed to the heavier using twin’s excessive substance use since the twins are matched for their genetic constitution and shared rearing experiences. This type of natural experiment, combining a longitudinal design with a twin differences design, provides one of the most powerful approaches that can be applied to study how substance use affects brain development, and in turn, how impaired brain development affects subsequent mental health and psychological adjustment in adulthood. This work, funded by grants from the National Institute on Drug Abuse that run through 2019, involves the study of over 700 twin pairs, and includes structural and functional MRI measures as well as EEG, neuropsychological, and mental health assessments.
I am also interested in the detection of deception. Most of my work in this area deals with the validity of conventionally applied lie detection techniques and their use in forensic settings. However, I am also interested in how novel techniques based on the measure of brain potentials can be used to probe the memory of criminal suspects.