[Formula: see text]Working memory and behavioral inhibition in boys with ADHD: An experimental examination of competing models

Working memory (WM) and behavioral inhibition impairments have garnered significant attention as candidate core features, endophenotypes, and/or associated neurocognitive deficits of attention-deficit/hyperactivity disorder (ADHD). The relationship between ADHD-related WM and inhibition deficits remains relatively unclear, however, with inferences about the constructs' directional relationship stemming predominantly from correlational research. The current study utilized a dual-task paradigm to experimentally examine the relationship between ADHD-related WM and behavioral inhibition deficits. A total of 31 boys (15 ADHD and 16 typically developing [TD]) aged 8-12 years completed WM (1-back and 2-back), behavioral inhibition (stop-signal task [SST]), and dual-condition (1-back/SST and 2-back/SST) experimental tasks. Children with ADHD exhibited significant, large-magnitude WM deficits for the 1-back condition but were not significantly different from children in the TD group for the 2-back, 1-back/SST, and 2-back/SST conditions. Children with ADHD also exhibited significant inhibition deficits for the SST, 1-back/SST, and 2-back/SST conditions, but the within-group effect was not significant. The findings suggest that ADHD-related stop-signal demands are upstream, or compete for, resources involved in controlled-focused attention and/or other central executive (CE), WM processes.

Hyperactivity in boys with attention-deficit/hyperactivity disorder (ADHD): The role of executive and non-executive functions

Motor activity of boys (age 8-12 years) with (n=19) and without (n=18) ADHD was objectively measured with actigraphy across experimental conditions that varied with regard to demands on executive functions. Activity exhibited during two n-back (1-back, 2-back) working memory tasks was compared to activity during a choice-reaction time (CRT) task that placed relatively fewer demands on executive processes and during a simple reaction time (SRT) task that required mostly automatic processing with minimal executive demands. Results indicated that children in the ADHD group exhibited greater activity compared to children in the non-ADHD group. Further, both groups exhibited the greatest activity during conditions with high working memory demands, followed by the reaction time and control task conditions, respectively. The findings indicate that large-magnitude increases in motor activity are predominantly associated with increased demands on working memory, though demands on non-executive processes are sufficient to elicit small to moderate increases in motor activity as well.

Visuospatial working memory underlies choice-impulsivity in boys with attention-deficit/hyperactivity disorder

The present study examined the directional relationship between choice-impulsivity and separate indices of phonological and visuospatial working memory performance in boys (aged 8-12 years) with (n=16) and without ADHD (n=19). Results indicated that high ratings of overall ADHD, inattention, and hyperactivity were significantly associated with increased impulsivity and poorer phonological and visuospatial working memory performance. Further, results from bias-corrected bootstrapped mediation analyses revealed a significant indirect effect of visuospatial working memory performance, through choice-impulsivity, on overall ADHD, inattention, and hyperactivity/impulsivity. Collectively, the findings suggest that deficits of visuospatial working memory underlie choice-impulsivity, which in turn contributes to the ADHD phenotype. Moreover, these findings are consistent with a growing body of literature that identifies working memory as a central neurocognitive deficit of ADHD.

Working memory deficits in boys with attention deficit/hyperactivity disorder (ADHD): An examination of orthographic coding and episodic buffer processes

The episodic buffer component of working memory was examined in children with attention deficit/hyperactivity disorder (ADHD) and typically developing peers (TD). Thirty-two children (ADHD = 16, TD = 16) completed three versions of a phonological working memory task that varied with regard to stimulus presentation modality (auditory, visual, or dual auditory and visual), as well as a visuospatial task. Children with ADHD experienced the largest magnitude working memory deficits when phonological stimuli were presented via a unimodal, auditory format. Their performance improved during visual and dual modality conditions but remained significantly below the performance of children in the TD group. In contrast, the TD group did not exhibit performance differences between the auditory- and visual-phonological conditions but recalled significantly more stimuli during the dual-phonological condition. Furthermore, relative to TD children, children with ADHD recalled disproportionately fewer phonological stimuli as set sizes increased, regardless of presentation modality. Finally, an examination of working memory components indicated that the largest magnitude between-group difference was associated with the central executive. Collectively, these findings suggest that ADHD-related working memory deficits reflect a combination of impaired central executive and phonological storage/rehearsal processes, as well as an impaired ability to benefit from bound multimodal information processed by the episodic buffer.

Working memory contributes to elevated motor activity in adults with ADHD: an examination of the role of central executive and storage/rehearsal processes

OBJECTIVE

The relationship between working memory (WM) and objectively measured motor activity was examined in adults with ADHD and healthy controls (HCs).

METHOD

Thirty-five adults (ADHD = 20, HC = 15) were grouped using self-report and collateral-report measures in addition to a semistructured clinical interview. All participants completed control conditions with minimal WM demands, and separate phonological (PH) and visuospatial (VS) WM tasks with recall demands ranging from four to seven stimuli.

RESULTS

The ADHD group exhibited significantly more motor activity relative to the HC group, and both groups exhibited greater activity during PH and VS WM tasks, relative to control conditions. Finally, the central executive (CE) and PH storage/rehearsal subsystems were associated with large-magnitude between-group differences in activity.

CONCLUSION

Findings suggest that increased demands on WM, particularly the CE and PH storage/rehearsal, contribute to ADHD-related hyperactivity, though a portion of excessive motor activity in adults with ADHD may occur independently of WM demands.

Symptoms of attention-deficit/hyperactivity disorder (ADHD) moderate suicidal behaviors in college students with depressed mood

OBJECTIVE

College students with attention-deficit/hyperactivity disorder-related hyperactive/impulsive (HI) and/or inattentive (IA) symptoms may be at greater risk for suicidal behavior due to core and secondary symptoms that increase their potential to engage in behaviors that put them at risk for suicidal behavior. Consequently, the current study examined the moderating effect of combined HI/IA symptoms, in addition to independent HI and IA symptoms on the relationship between depressed mood and suicidal thoughts and behavior.

METHOD

A sample of 1,056 undergraduate students (61.5% female, 96.4% aged 18-24 years) provided self-report ratings of mood, suicidal behavior (thoughts, self-harm, attempts, and need for medical attention), and current HI/IA symptoms.

RESULTS

Significant moderation effects were detected, such that greater HI/IA symptoms were associated with a stronger relationship between depressed mood and suicidal ideation and attempts, but not self-harm. Current HI and IA symptoms significantly moderated the relationship between depressed mood and suicidal thoughts and suicide attempts, but did not moderate the relationship between depressed mood and self-harm and need for medical attention.

CONCLUSIONS

The current findings suggest that the presence of combined HI/IA symptoms conveys increased suicide risk for depressed college students. Additionally, results suggest a complex relationship between independent HI and IA symptoms and severe suicidal outcomes.

Working memory deficits in adults with attention-deficit/hyperactivity disorder (ADHD): an examination of central executive and storage/rehearsal processes

The current study was the first to use a regression approach to examine the unique contributions of central executive (CE) and storage/rehearsal processes to working memory (WM) deficits in adults with ADHD. Thirty-seven adults (ADHD = 21, HC = 16) completed phonological (PH) and visuospatial (VS) working memory tasks. While both groups performed significantly better during the PH task relative to the VS task, adults with ADHD exhibited significant deficits across both working memory modalities. Further, the ADHD group recalled disproportionately fewer PH and VS stimuli as set-size demands increased. Overall, the CE and PH storage/rehearsal processes of adults with ADHD were both significantly impaired relative to those of the healthy control adults; however, the magnitude of the CE effect size was much smaller compared to previous studies of children with the disorder. Collectively, results provide support for a lifelong trajectory of WM deficits in ADHD.

Moderators of working memory deficits in children with attention-deficit/hyperactivity disorder (ADHD): a meta-analytic review

Working memory has assumed a prominent role as a primary neurocognitive deficit or endophenotype in extant models of attention-deficit/hyperactivity disorder (ADHD). The current study updated previous reviews and employed meta-analytic techniques to examine a broad range of moderating variables of effect size heterogeneity across phonological and visuospatial working memory tasks. Collectively, results revealed large between-group effect sizes across both working memory domains. In addition, several sample (percent female) and task (number of experimental trials, recall vs. recognition tasks, and demands on the central executive) moderating variables explained significant effect size variability among phonological and visuospatial studies. These findings suggest that children with ADHD exhibit statistically significant, large magnitude working memory deficits relative to their typically developing peers.

The selenite-exchangeable metabolic pool in humans: a new concept for the assessment of selenium status

An in vivo isotope-dilution approach is considered for assessment of selenium status in human subjects. The approach depends upon the dilution of a single dose of the stable isotope 74SeO3(2-) in the selenite-exchangeable metabolic pool. Data from six metabolic protocols, conducted with healthy North American males, are presented in order to analyze characteristics of this pool. Pool size (WSe-EMP) correlated positively with daily selenium intake in subjects consuming diets of known and variable selenium content. When subjects were given a selenium-adequate or -restricted diet for 30 d, WSe-EMP,7d decreased from 4.49 +/- 0.28 to 3.76 +/- 0.22 mg (p less than 0.05). The corresponding 24-h urinary selenium concentration dropped from 0.556 +/- 0.035 to 0.341 +/- 0.058 mumol/d (means +/- 1 SEM). Route of administration (iv vs po) had no apparent effect on WSe-EMP. In subjects of similar selenium status, the WSe-EMP was reproducible within the expected uncertainties of the method. This approach may be suitable for assessment of selenium status for a wide range of chronic intakes.

Short-term dietary selenium restriction in young adults: quantitative studies with the stable isotope 74SeO3(2-)

A 45 d metabolic study was carried out in four young adult male North American residents consuming a controlled diet based on an amino acid mixture. During the initial 10 d, total daily selenium intake was adjusted to 107.7 (SE 0.1) microgram/d, which was reduced to 11.4 (SE 0.1) microgram/d for the remaining 35 d. Two doses of a stable isotope (74SeO3(2-)) were administered orally in the post-absorptive state on days 4 and 39 of the study. Se balance (faecal + urinary excretion) as well as stable isotope excretion studies were carried out for the entire 45 d period; blood plasma and erythrocyte Se concentrations were also monitored. Plasma Se concentrations (microgram/ml) fell progressively from the initial value of 0.132 (SE 0.007) to 0.083 (SE 0.008) at the end of the study. The erythrocyte concentrations of Se did not vary in a consistent manner (average value for the entire study 0.147 (SE 0.002) microgram/ml). Faecal excretion of unenriched Se decreased from 66 (SE 6) microgram/d for days 1-10 to 10.2 (SE 0.8) microgram/d for days 14-40. Mean urinary excretions of the unenriched Se were 43.9 (SE 2.8) microgram/d (days 1-10) and 26.9 (SE 4.6) microgram/d (days 14-40). Total balance (intake-faecal excretion-urinary excretion) for unenriched Se was (microgram/d):-18 (SE 7) days 10-19, -17 (SE 2) days 19-39, -5 (SE 1) days 38-45. Fractional absorption of the ingested label was 0.529 (SE 0.032) and 0.542 (SE 0.038) for the Se-adequate and Se-restricted phases of the study. However, urinary excretion of the absorbed label was reduced from 6.57 (SE 0.73)% for day 1 of the Se-adequate phase to only 3.32 (SE 0.26)% for day 1 of the Se-restricted phase. Similar observations were also made for day 7 of each phase. These findings indicate that immediate contribution of ingested Se to the urinary Se pool is small.

Dynamics of selenite metabolism in young men: studies with the stable isotope tracer method

Dynamics of selenite metabolism in young adult North American men were studied using an amino acid diet and the stable isotope tracer methodology during a short-term selenium replete-restriction phase. During the initial 10 days subjects consumed the diet providing a total daily selenium intake of 107.7 +/- 0.1 micrograms mostly as selenite. This was followed by selenium restriction at 11.4 +/- 0.1 micrograms/day (as impurities from diet components) for the next 34 days. Kinetic studies with the stable isotope tracer 74SeO32- were carried out on days 4 and 39 of the study. Kinetics of excretion of the tracer in feces and urine were followed from which body retention curves were constructed. The retention curves were resolved into two exponential decay components with half-lives of 2.4 +/- 0.3 and 162 +/- 9 days (mean +/- 1 SEM), respectively. Retention data and urine isotope enrichment curves were combined to determine dynamics of changes in the apparent body pool size for selenite (10.4 mg at t----infinity) as well as rates of turnover for this parameter.