Biological and social influences on cognitive control processes dependent on prefrontal cortex

Abstract

Cognitive control functions ("executive functions" [EFs] such as attentional control, self-regulation, working memory, and inhibition) that depend on prefrontal cortex (PFC) are critical for success in school and in life. Many children begin school lacking needed EF skills. Disturbances in EFs occur in many mental health disorders, such as ADHD and depression. This chapter addresses modulation of EFs by biology (genes and neurochemistry) and the environment (including school programs) with implications for clinical disorders and for education. Unusual properties of the prefrontal dopamine system contribute to PFC's vulnerability to environmental and genetic variations that have little effect elsewhere. EFs depend on a late-maturing brain region (PFC), yet they can be improved even in infants and preschoolers, without specialists or fancy equipment. Research shows that activities often squeezed out of school curricula (play, physical education, and the arts) rather than detracting from academic achievement help improve EFs and enhance academic outcomes. Such practices may also head off problems before they lead to diagnoses of EF impairments, including ADHD. Many issues are not simply education issues or health issues; they are both.

Fig. 1

Mechanism of action of methylphenidate.

Fig. 2

Comparison of the performance of PKU children whose blood Phe levels were 6–10 mg/dL (360–600 mmol/L; labeled the “High Phe” group) with the performance of four comparison groups on tasks that assess executive functioning (the top and middle panels) and a task that does not tax EFs (bottom panel). At each age range investigated (the top panel shows one of the age ranges and the middle panel shows another), and on all EF measures requiring working memory and inhibitory control, the PKU children with relatively high Phe levels (though still within the clinically accepted range at the time) performed significantly worse no matter who they were compared with (other PKU children with lower Phe levels [Phe levels of 2–6 mg/dL, 120–360 mmol/L; labeled the “Low Phe” group], their own siblings, matched controls, or children from the general population). They were not impaired on any of the ten control measures (one shown in bottom panel), most of which required the functions of parietal cortex or the medial temporal lobe. (Modified with permission from Diamond et al., 1997).

Fig. 3

Performance of children by COMT genotype on four cognitive measures. Children homozygous for COMT Met-158 performed significantly better (Wilcoxon t = 126.0, p<0.01) than children homozygous for the COMT Val-158 genotype on the Dots-Mixed task, which requires holding two higher-order rules in mind and switching between inhibiting a prepotent response and making it, and is sensitive to the level of dopamine in PFC. All groups performed comparably on all control tasks (i.e., there was no effect of COMT genotype on any control task): (1) self-ordered pointing, which depends on PFC but is not sensitive to the level of dopamine in PFC; (2) recall memory, which depends on the medial temporal lobe; and (3) mental rotation, which depends on parietal cortex. To control for the effect of age, age mean difference scores were used. For each task, the mean percentage of correct responses for the subject’s age in years was subtracted from the subject’s percentage of correct responses, yielding an age difference score. This partialled out any effect of age. Gender was not significantly related to performance on any of these three cognitive tasks. (From Diamond et al., 2004, with permission).

Fig. 4

Illustration of how, if males and females have different baseline levels of dopamine in PFC, that would account for the differential effects of slight stress on males and females (with slight stress being beneficial for males’ EFs but detrimental for females’ EFs).

Fig. 5

Photograph of two children engaged in Buddy Reading. Note the line drawing of an ear in the hand of the girl listening to the other girl. Photograph by Morey Kitzman, reprinted from the supplementary online material for Diamond et al. (2007) with permission.

Fig. 6

Photograph of a child performing the Hearts & Flowers task (which used to be called Dots-Mixed [see Fig. 3]) and comparison of the performance of Kindergarten children in Tools of the Mind (lighter gray in print version; blue in online version) with the performance of children from the same neighborhood, closely matched on demographics, in a different kindergarten program (darker gray in print version; pink in online version) on tasks that assess EFs. All differences are significant, but the benefit of Tools of the Mind on the easier conditions (Hearts & Flowers Incongruent and Flanker) was much smaller than on the more EF-demanding conditions (Hearts & Flowers Mixed and Reverse Flanker). For the first set of three graphs (A), the dependent measure is percentage of correct responses. For the last graph (B), the dependent measure is percentage of children. Photograph is by Martin Dee. The graphs are reprinted from Diamond et al. (2007) with permission.