Adele Diamond

Interventions Shown to Aid Executive Function Development in Children 4 to 12 Years Old

To be successful takes creativity, flexibility, self-control, and discipline. Central to all those are executive functions, including mentally playing with ideas, giving a considered rather than an impulsive response, and staying focused. Diverse activities have been shown to improve children’s executive functions: computerized training, noncomputerized games, aerobics, martial arts, yoga, mindfulness, and school curricula. All successful programs involve repeated practice and progressively increase the challenge to executive functions. Children with worse executive functions benefit most from these activities; thus, early executive-function training may avert widening achievement gaps later. To improve executive functions, focusing narrowly on them may not be as effective as also addressing emotional and social development (as do curricula that improve executive functions) and physical development (shown by positive effects of aerobics, martial arts, and yoga).

Biological processes in prevention and intervention: The promotion of self-regulation as a means of preventing school failure

This paper examines interrelations between biological and social influences on the development of self-regulation in young children and considers implications of these interrelations for the promotion of self-regulation and positive adaptation to school. Emotional development and processes of emotion regulation are seen as influencing and being influenced by the development of executive cognitive functions, including working memory, inhibitory control, and mental flexibility important for the effortful regulation of attention and behavior. Developing self-regulation is further understood to reflect an emerging balance between processes of emotional arousal and cognitive regulation. Early childhood educational programs that effectively link emotional and motivational arousal with activities designed to exercise and promote executive functions can be effective in enhancing self-regulation, school readiness, and school success.

Development of an aspect of executive control: Development of the abilities to remember what I said and to “Do as I say, not as I do”

Lurias tapping test (tap once when E taps twice, tap twice when E taps once) was administered to 160 children (80 males, 80 females) between 3 1/2 to 7 years old. Older children were faster and more accurate than younger children, with most of the improvement occurring by the age of 6. All children tested demonstrated understanding of the instructions during the pretest, and most started out performing well, but younger subjects could not sustain this. Over the 16 trials, percentage of correct responses decreased, especially among younger subjects. Performance here was compared with performance on the day-night Stroop-like task. The most common error on both tasks was to comply with only one of the two rules. Other errors included tapping many times regardless of what the experimenter did and doing the same thing as the experimenter, rather than the opposite. It is suggested that the tapping task requires both the ability to hold two rules in mind and the ability to inhibit a strong response tendency, that these abilities improve between 3-6 years of age, and that this improvement may reflect important changes within frontal cortex during this period of life.

Comparison of human infants and rhesus monkeys on Piaget's AB task: evidence for dependence on dorsolateral prefrontal cortex

SummaryThis paper reports evidence linking dorsolateral prefrontal cortex with one of the cognitive abilities that emerge between 7.5–12 months in the human infant. The task used was Piagets Stage IV Object Permanence Test, known as AB (pronounced “A not B”). The AB task was administered (a) to human infants who were followed longitudinally and (b) to intact and operated adult rhesus monkeys with bilateral prefrontal and parietal lesions. Human infants displayed a clear developmental progression in AB performance, i.e., the length of delay required to elicit the AB error pattern increased from 2–5 s at 7.5–9 months to over 10 s at 12 months of age. Monkeys with bilateral ablations of dorsolateral prefrontal cortex performed on the AB task as did human infants of 7.5–9 months; i.e., they showed the AB error pattern at delays of 2–5 s and chance performance at 10 s. Unoperated and parietally operated monkeys succeeded at delays of 2, 5, and 10 s; as did 12 month old human infants. AB bears a striking resemblance to Delayed Response, the classic test for dorsolateral prefrontal function in the rhesus monkey, and indeed performance on AB and Delayed Response in the same animals in the present study was fully comparable. These findings provide direct evidence that AB performance depends upon dorsolateral prefrontal cortex in rhesus monkeys and indicates that maturation of dorsolateral prefrontal cortex may underlie the developmental improvement in AB performance of human infants from 7.5–12 months of age. This improvement marks the development of the ability to hold a goal in mind in the absence of external cues, and to use that remembered goal to guide behavior despite the pull of previous reinforcement to act otherwise. This confers flexibility and freedom to choose and control what one does.

Prefrontal cortex cognitive deficits in children treated early and continuously for PKU.

To begin to study the importance of dopamine for executive function abilities dependent on prefrontal cortex during early childhood, the present investigation studied children in whom we predicted reduced dopamine in prefrontal cortex but otherwise normal brains. These are children treated early and continuously for the metabolic disorder phenylketonuria (PKU). Untreated PKU is the most common biochemical cause of mental retardation. The root problem is an inability to convert one amino acid, phenylalanine (Phe), into another, tyrosine (Tyr), the precursor of dopamine. Phe levels in the bloodstream soar; Tyr levels fall. Treatment with a diet low in Phe reduces the Phe:Tyr imbalance but cannot eliminate it. We hypothesized that the resultant modest elevation in the ratio of Phe to Tyr in the blood, which results in slightly less Tyr reaching the brain, uniquely affects the cognitive functions dependent on prefrontal cortex because of the special sensitivity of prefrontally projecting dopamine neurons to small decreases in Tyr. In a 4-year longitudinal study, we found that PKU children whose plasma Phe levels were three to five times normal (6-10 mg/dl) performed worse than other PKU children with lower Phe levels, matched controls, their own siblings, and children from the general population on tasks that required the working memory and inhibitory control abilities dependent on dorsolateral prefrontal cortex. The impairment was as evident in our oldest age range (3 1/2-7 years) as it was in the youngest (6-12 months). The higher a childs Phe level, the worse that childs performance. Girls were more adversely affected than boys. The deficit appears to be selective, affecting principally one neural system, since even PKU children with Phe levels three to five times normal performed well on the 13 control tasks. Clinical implications for the treatment of PKU and other neurodevelopmental disorders are discussed.

Developmental time course in human infants and infant monkeys, and the neural bases of, inhibitory control in reaching.

Development appears to proceed by destruction and inhibition, as well as by construction and acquisition. For example, neural development involves, in part, pruning back an oversupply of neurons and an exuberance of axonal projections (see, e.g., Frost, this volume; Innocenti & Clarke, 1984). There are more nerve cells at birth in the neocortex of monkeys and humans than at any time thereafter (e.g., Rakic, 1974; 1985). Motor development and cognitive development, likewise, are made possible, in part, by the inhibition of reflexive and automatic reactions (e.g., Diamond & Gilbert, 1989). More and more regions of frontal cortex are being found to play a role in inhibition, although various subdivisions of frontal cortex appear to participate in different aspects of inhibition. Frontal cortex is by far the largest area of cortex in the human brain, it has increased the most in size (and in the proportion of brain mass devoted to it) over the course of evolution, and it takes longer to reach maturity than any other area of the brain (frontal cortex only becomes fully mature around puberty [e.g., Diamond, in press, a]). There is general agreement that the most anterior regions of frontal cortex (i.e., prefrontal cortex) subserve the highest cognitive abilities, the crowning intellectual achievements of the human race. The role of frontal cortex in inhibition is probably critical to its ability to subserve complex cognitive operations. Take, for example, the importance of prefrontal cortex for focusing attention. The role of frontal cortex in aiding attention appears to depend on the inhibitory functions of frontal cortex. Frontal cortex activity is critical to reduce distractibility

Helping children apply their knowledge to their behavior on a dimension‐switching task

To investigate why 3-year-olds have difficulty in switching sorting dimensions, children of 3 and 4 years were tested in one of four conditions on Zelazos card sort task: standard, sleeve, label and face-up. In the standard condition, children were required to sort blue-truck and red-star cards under either a blue-star or red-truck model card, first by color or shape, and then by the other dimension. Here 3-year-olds sorted correctly until the dimension changed; they continue to sort by the initial dimension. The sleeve condition (placing the sorting cards in an envelope prior to sorting) had little effect. In the label condition, the child labeled the relevant sorting dimension on each trial. Most 3-year-olds succeeded; evidently their labeling helped them refocus their attention, overcoming ‘attentional inertia’ (the pull to continue attending to the previously relevant dimension). In the face-up condition, attentional inertia was strengthened because sorted cards were left face-up; 4-year-olds performed worse than in the standard condition. We posit that attentional inertia is the core problem for preschoolers on the card sort task.

Attention-deficit disorder (attention-deficit/hyperactivity disorder without hyperactivity): A neurobiologically and behaviorally distinct disorder from attention-deficit/hyperactivity disorder (with hyperactivity)

Most studies of attention-deficit/hyperactivity disorder (ADHD) have focused on the combined type and emphasized a core problem in response inhibition. It is proposed here that the core problem in the truly inattentive type of ADHD (not simply the subthreshold combined type) is in working memory. It is further proposed that laboratory measures, such as complex-span and dual-task dichotic listening tasks, can detect this. Children with the truly inattentive type of ADHD, rather than being distractible, may instead be easily bored, their problem being more in motivation (underarousal) than in inhibitory control. Much converging evidence points to a primary disturbance in the striatum (a frontal-striatal loop) in the combined type of ADHD. It is proposed here that the primary disturbance in truly inattentive-type ADHD (ADD) is in the cortex (a frontal-parietal loop). Finally, it is posited that these are not two different types of ADHD, but two different disorders with different cognitive and behavioral profiles, different patterns of comorbidities, different responses to medication, and different underlying neurobiologies.

Activities and Programs That Improve Children’s Executive Functions

Executive functions (EFs; e.g., reasoning, working memory, and self-control) can be improved. Good news indeed, since EFs are critical for school and job success and for mental and physical health. Various activities appear to improve children’s EFs. The best evidence exists for computer-based training, traditional martial arts, and two school curricula. Weaker evidence, though strong enough to pass peer review, exists for aerobics, yoga, mindfulness, and other school curricula. Here I address what can be learned from the research thus far, including that EFs need to be progressively challenged as children improve and that repeated practice is key. Children devote time and effort to activities they love; therefore, EF interventions might use children’s motivation to advantage. Focusing narrowly on EFs or aerobic activity alone appears not to be as efficacious in improving EFs as also addressing children’s emotional, social, and character development (as do martial arts, yoga, and curricula shown to improve EFs). Children with poorer EFs benefit more from training; hence, training might provide them an opportunity to “catch up” with their peers and not be left behind. Remaining questions include how long benefits of EF training last and who benefits most from which activities.

The Development and Neural Bases of Memory Functions as Indexed by the AB and Delayed Response Tasks in Human Infants and Infant Monkeysa

One of the classic markers of developmental change in infants between 7%-12 months of age is improved performance on “the a task” (pronounced “A not B”). This task was first devised by Piaget (1954 [1937]) and has been used by researchers throughout the world to study psychological development in babies (for reviews see Gratch, 1975; Schuberth, 1982; Harris, 1986; Wellman, Cross & Bartsch, 1987). One of the most useful tasks in the study of brain-behavior relations is a task called “delayed response.” It was first introduced for this purpose by Jacobsen (1935; 1936) and has been widely used ever since to study brain function in monkeys and other animals (for reviews see Nauta, 1971; Rosvold, 1972; Rosenkilde, 1979; Fuster, 1980). Delayed response has been particularly useful in this regard because success on the task has been systematically linked to proper functioning of a discrete neural circuit that comprises dorsolateral prefrontal cortex and the structures with which it is interconnected. As it turns out, the a and delayed response tasks are very similar, even though they were developed independently and for almost 50 years scientists working with one task did not know of the work of scientists with the other. Indeed, it has recently been established that infants show the same developmental progression on delayed response as they show on AB (Diamond & Doar, 1989), and success on a depends on functioning of the same neural circuit as does success on delayed response (Diamond & Goldman-Rakic, 1989).