the core cognitive deficit of those with ADHD-I is working memory, or, as she coined in her recent paper on the subject, "childhood-onset dysexecutive syndrome". However, two more recent studies by Barkley found that while children and adults with SCT had some deficits in executive functions (EF) in everyday life activities, they were primarily of far less magnitude and largely centered around problems with self-organization and problem-solving. Even then, analyses showed that most of the difficulties with EF deficits were the result of overlapping ADHD symptoms that may co-exist with SCT rather than being attributable to SCT itself. More research on the link of SCT to EF deficits is clearly indicated—but, as of this time, SCT does not seem to be as strongly associated with EF deficits as is ADHD. Causes Unlike ADHD, the general causes of SCT symptoms are almost unknown, though one recent study of twins suggested that the condition appears to be nearly as heritable or genetically influenced in nature as ADHD. That is to say that the majority of differences among individuals in these traits in the population may be due mostly to variation in their genes. The heritability of SCT symptoms in that study was only slightly lower than that for ADHD symptoms with a somewhat greater share of trait variation being due to unique environmental events. For instance, in ADHD, the genetic contribution to individual differences in ADHD traits typically averages between 75 and 80% and may even be as high as 90%+ in some studies. That for SCT maybe 50–60%. Little is known about the neurobiology of SCT. But the SCT symptoms seem to indicate that the posterior attention networks may be more involved here than the prefrontal cortex region of the brain and difficulties with working memory so prominent in ADHD. This hypothesis gained greater support following a 2015 neuroimaging study comparing ADHD inattentive symptoms and SCT symptoms in adolescents: It found that SCT was associated with a decreased activity in the left superior parietal lobule (SPL), whereas inattentive symptoms were associated with other differences in activation. A 2018 study showed an association between SCT and specific parts of the frontal lobes, differing from classical ADHD neuroanatomy. A study showed a small link between thyroid functioning and SCT symptoms suggesting that thyroid dysfunction is not the cause of SCT. High rates of SCT were observed in children who had prenatal alcohol exposure