Intraindividual Reaction Time Variability Research Articles

The impact of physical activity and sex differences on intraindividual variability in inhibitory performance in older adults

ABSTRACTIt is well-known that processing speed and executive functions decline with advancing age. However, physical activity (PA) has a positive impact on cognitive performances in aging, specifically for inhibition. Less is known concerning intraindividual variability (iiV) in reaction times. This study aims to investigate the influence of PA and sex differences on iiV in inhibitory performance during aging. Healthy adults were divided into active and sedentary groups according to PA level. To analyse iiV in reaction times, individual mean, standard deviation and the ex-Gaussian parameters were considered. An interaction between activity level and sex was revealed, sedentary females being slower and more variable than sedentary men. No sex differences were found in the active groups. These results indicate that the negative impact of sedentariness on cognitive performance in older age is stronger for females. The present findings underline the need to consider sex differences in active aging approaches.

Is intraindividual reaction time variability an independent cognitive predictor of mortality in old age? Findings from the Sydney Memory and Ageing Study.

Intraindividual variability of reaction time (IIVRT), a proposed cognitive marker of neurobiological disturbance, increases in old age, and has been associated with dementia and mortality. The extent to which IIVRT is an independent predictor of mortality, however, is unclear. This study investigated the association of IIVRT and all-cause mortality while accounting for cognitive level, incident dementia and biomedical risk factors in 861 participants aged 70–90 from the Sydney Memory and Ageing Study. Participants completed two computerised reaction time (RT) tasks (76 trials in total) at baseline, and comprehensive medical and neuropsychological assessments every 2 years. Composite RT measures were derived from the two tasks—the mean RT and the IIVRT measure computed from the intraindividual standard deviation of the RTs (with age and time-on-task effects partialled out). Consensus dementia diagnoses were made by an expert panel of clinicians using clinical criteria, and mortality data were obtained from a state registry. Cox proportional hazards models estimated the association of IIVRT and mean RT with survival time over 8 years during which 191 (22.2%) participants died. Greater IIVRT but not mean RT significantly predicted survival time after adjusting for age, sex, global cognition score, cardiovascular risk index and apolipoprotein ɛ4 status. After excluding incident dementia cases, the association of IIVRT with mortality changed very little. Our findings suggest that greater IIVRT uniquely predicts shorter time to death and that lower global cognition and prodromal dementia in older individuals do not explain this relationship.

NEURAL CORRELATES OF REACTION TIME VARIABILITY IN OLDER ADULTS PERFORMING A MULTI-SOURCE INTERFERENCE TASK

A growing body of literature describes older adults showing decline in cognitive control (top-down executive control) that is associated with frontal lobe change. Traditional neuropsychological tests examining frontal dysfunction, such as the Stroop and the Trail Making tests, measure individual's top-down control ability by comparing the time taken to complete the task in control condition and the interference condition. Trial-by-trial intra-individual reaction time (RT) variability in cognitive control tasks, however, could also be a sensitive measure of frontal integrity, since it has been shown that frontal involvement is critical in maintaining cognitive stability by minimizing fluctuation of cognitive performance. In this study, we purported to investigate the neural correlates of intra-individual RT variability in an experimental cognitive control task, namely the Multi-Source Interference Task (MSIT). Utilizing functional magnetic resonance imaging (fMRI), we investigated the brain regions activated when healthy older adults (n=52) performed the MSIT, which consists of interference and control conditions. Regional activation that was significantly different in the interference condition compared to the control condition was examined to find brain regions involved in inhibitory control. Within the regions found to be involved in inhibitory control, we identified regions that were specifically associated with the intra-individual RT variability. Inhibitory success was correlated with smaller intra-individual variability of RT, while the magnitude of the variability was reflected in the activation of the frontal regions, such as the left middle and left inferior frontal gyri, as well as the left supramarginal gyrus. Individuals with greater intra-individual variability during the MSIT activated the inhibitory control network to a greater magnitude, possibly reflecting the increased demand for cognitive control network due to their less efficient inhibitory control system. This is consistent with previous findings that showed greater intra-individual variability in dementia patients with frontal involvement compared to those with Alzheimer's disease. Increase in intra-individual variability of RT has also been shown to be observed in people with MCI, suggesting the measure as a promising behavioral index that reflects frontal or frontoparietal integrity.

CHARACTERISING SUBJECTIVE COGNITIVE IMPAIRMENT

Subjective cognitive impairment (SCI) is increasingly recognised in both the clinical and research arena as a risk factor for mild cognitive impairment (MCI) and dementia, particularly Alzheimer's disease (AD). However, in comparison to MCI and AD, SCI remains relatively poorly characterised, with debate persisting regarding its clinical relevance and importance. Possible explanations for the debate is a lack of awareness amongst clinicians regarding what SCI is, what aspects of brain function it may impact on, and the influence such functional detriment may have upon quality of life and well-being. A principal aim in both the clinical and research arena is to further characterise what functions may be abnormal in SCI in addition to reported feelings of changes in memory and cognition. The present cross-sectional study was designed to characterise SCI in the general-public (i.e., not medically diagnosed) with respect to visual attention-related processing speed (RT) and the intra-individual variability of reaction time (IIVRT) and in relation to various factors including the cognition, memory, mood, anxiety, neuroticism and quality of life of the participants. The results revealed that at group level there were no significant differences in RT and IIVRT between the SCI and non-SCI group. However, within-group correlational analysis identified that within the SCI group, there was evidence of slowing RT and increased IIVRT. In addition, at group level those in the SCI group were also experiencing significant distress in relation to anxiety, depression and poor QOL. Within the current study it is not possible to identify cause and effect, therefore the individuals in the SCI group cannot simply be dismissed as being ‘worried well’. They still require a full-comprehensive assessment, a follow-up assessment, and appropriate support. This presentation will reveal and explore what characteristics of SCI were identified within this study and what the next steps are (i.e. the testing of a clinical population).

A Systematic Review of Longitudinal Associations Between Reaction Time Intraindividual Variability and Age-Related Cognitive Decline or Impairment, Dementia, and Mortality

Intraindividual variability (IIV) in reaction time refers to the trial-to-trial fluctuations in responding across a given cognitive task. Cross-sectional research suggests that IIV increases with normal and neuropathological ageing and it may serve as a marker of neurobiological integrity. This raises the possibility that IIV may also predict future cognitive decline and, indeed, neuropathology. Therefore, we conducted a systematic review to address these issues. A search of electronic databases Embase, Medline, PsycINFO, and Web of Science was completed on May 17, 2016 that identified longitudinal investigations of IIV in middle-aged or older adults. A total of 688 studies were initially identified of which 22 met the inclusion criteria. Nine included longitudinal IIV measures and 17 predicted subsequent outcome (cognitive decline or impairment, dementia, mortality) from baseline IIV. The results suggested IIV increased over time, particularly in participants aged over 75 years. Greater baseline IIV was consistently associated with increased risk of adverse outcomes including cognitive decline or impairment, and mortality. Increased IIV over time is associated with normal ageing. However, further increases in IIV over and above those found in normal ageing may be a risk factor for future cognitive impairment or mortality. Measures of IIV may, therefore, have considerable potential as a supplement to existing clinical assessment to aid identification of individuals at risk of adverse outcomes such as dementia or death. (JINS, 2017, 23, 431-445).

Relationship between whole grain consumption and selective attention

IntroductionGreater habitual diet quality has been associated with weight regulation and reduced risk for chronic diseases including cardiovascular disease and Type‐2 diabetes. Previous studies have outlined the role of markers of diet quality ‐ wholegrain consumption in particular ‐ in reducing the risk for these diseases. However, the role of wholegrain consumption in cognitive function remains unclear. Studying these relationships may contribute to the body of literature linking whole grain consumption to improved physical and mental health.MethodsAdults between 25–45 years (N=76, 32 males) reported their dietary intake using the National Cancer Institute's (NCI) Diet History Questionnaire II (DHQII). Overall diet quality was assessed using the Healthy Eating Index (HEI‐2010) and whole grain consumption was measured using the whole grain component of the HEI‐2010. Selective attention was assessed using a modified Eriksen flanker task. Overall intellectual ability (IQ) and whole body adiposity (%Fat) was measured using the Kaufman Brief Intelligence Test and dual energy x‐ray absorptiometry, respectively.ResultsPartial correlations were conducted to examine relationships between whole grain consumption and flanker task variables following adjustment of age, sex, IQ, and total HEI‐2010 score. Whole grain consumption was positively related to accuracy in the both the congruent (r=0.37, P<0.01) and incongruent task conditions (r=0.28, P=0.02). Further, although no significant relationships were observed for mean response time (all Ps> 0.26), greater whole grain component scores were related to lower intraindividual variability (coefficient of variation) in reaction time during the incongruent (r=−0.33, P<0.01) but not congruent condition (r=−0.18, P=0.13).ConclusionThese data indicate that individuals with greater whole grain intake exhibited superior selective attention, as indicated by higher response accuracy and reduced variability in response time. Given that these relationships persisted even after adjusting for overall diet quality and important health and demographic factors provides support for the selective importance of whole grain intake for cognitive function. Future experimental studies are necessary to determine the impact of changes in whole grain intake on changes in cognitive function.Support or Funding InformationFunded by the Department of Kinesiology and Community Health at the University of Illinois and the Hass Avocado Board.

\u2018Two-level\u2019 measurements of processing speed as cognitive markers in the differential diagnosis of DSM-5 mild neurocognitive disorders (NCD)

Processing speed is an updated diagnostic factor for neurocognitive disorders (NCD) in DSM-5. This study investigated the characteristics of processing speed and their diagnostic values in NCD patients. A flanker test was conducted in 31 adults with NCD due to vascular disease (NCD-vascular), 36 patients with NCD due to Alzheimer’s disease (NCD-AD), and 137 healthy controls. The processing speed was evaluated using two measurements: mean reaction time (RT) and intra-individual variability of RT. Mean RT represents the global processing speed. Intra-individual variability of RT is the short-term fluctuation of RT and consists of two indices, which are intra-individual coefficient of variation of reaction time (ICV-RT) and intra-individual standard deviations (iSD). We observed elevated ICV-RT and iSD in NCD-AD and NCD-vascular patients. Additionally, there was a slowed RT in NCD-AD patients. The intra-individual variability of RT had a moderate power to differentiate NCD subgroups. The mean RT was able to discriminate the NCD-AD from NCD-vascular patients. Our findings highlight the clinical utility of the combined ‘two-level’ measurements of processing speed to distinguish between individuals with different cognitive status. Furthermore, the ‘two-level’ features of processing speed embedded in the psychometric property may also reflect the diverse aetiology underlying certain ‘disease-specific’ neurocognitive disorders.

Diminished modulation of preparatory sensorimotor mu rhythm predicts attention-deficit/hyperactivity disorder severity.

Attention-deficit/hyperactivity disorder (ADHD) is characterized by problems in regulating attention and in suppressing disruptive motor activity, i.e. hyperactivity and impulsivity. We recently found evidence that aberrant distribution of posterior α band oscillations (8-12 Hz) is associated with attentional problems in ADHD. The sensorimotor cortex also produces strong 8-12 Hz band oscillations, namely the μ rhythm, and is thought to have a similar inhibitory function. Here, we now investigate whether problems in distributing α band oscillations in ADHD generalize to the μ rhythm in the sensorimotor domain. In a group of adult ADHD (n = 17) and healthy control subjects (n = 18; aged 21-40 years) oscillatory brain activity was recorded using magnetoencephalography during a visuo-spatial attention task. Subjects had to anticipate a target with unpredictable timing and respond by pressing a button. Preparing a motor response, the ADHD group failed to increase hemispheric μ lateralization with relatively higher μ power in sensorimotor regions not engaged in the task, as the controls did (F 1,33 = 8.70, p = 0.006). Moreover, the ADHD group pre-response μ lateralization not only correlated positively with accuracy (r s = 0.64, p = 0.0052) and negatively with intra-individual reaction time variability (r s = -0.52, p = 0.033), but it also correlated negatively with the score on an ADHD rating scale (r s = -0.53, p = 0.028). We suggest that ADHD is associated with an inability to sufficiently inhibit task-irrelevant sensorimotor areas by means of modulating μ oscillatory activity. This could explain disruptive motor activity in ADHD. These results provide further evidence that impaired modulation of α band oscillations is involved in the pathogenesis of ADHD.

Intraindividual variability in reaction time before and after neoadjuvant chemotherapy in women diagnosed with breast cancer.

Women treated with chemotherapy for breast cancer experience subtle cognitive deficits. Research has focused on mean performance level, yet recent work suggests that within-person variability in reaction time performance may underlie cognitive symptoms. We examined intraindividual variability (IIV) in women diagnosed with breast cancer and treated with neoadjuvant chemotherapy. Patients (n=28) were assessed at baseline before chemotherapy (T1), approximately 1month after chemotherapy but prior to surgery (T2), and after surgery about 9months post chemotherapy (T3). Healthy women of similar age and education (n=20) were assessed at comparable time intervals. Using a standardized regression-based approach, we examined changes in mean performance level and IIV (eg, intraindividual standard deviation) on a Stroop task and self-report measures of cognitive function from T1 to T2 and T1 to T3. At T1, women with breast cancer were more variable than controls as task complexity increased. Change scores from T1 to T2 were similar between groups on all Stroop performance measures. From T1 to T3, controls improved more than women with breast cancer. IIV was more sensitive than mean reaction time in capturing group differences. Additional analyses showed increased cognitive symptoms reported by women with breast cancer from T1 to T3. Specifically, change in language symptoms was positively correlated with change in variability. Women with breast cancer declined in attention and inhibitory control relative to pretreatment performance. Future studies should include measures of variability, because they are an important sensitive indicator of change in cognitive function.

Associations between reaction time measures and white matter hyperintensities in very old age

In old age, a relationship has been reported between intraindividual variability (IIV) in reaction time and white matter integrity as evidenced by white matter hyperintensities (WMH). However, it is unclear how far such associations are due to incipient neurodegenerative pathology in the samples investigated. The present study examined the relationship between IIV and WMH in older individuals (N=526) drawn from the Sydney Memory and Ageing Study. Using a complex reaction time (RT) task, greater IIV and mean-RT were related to a higher WMH burden in the frontal lobe. Critically, significant associations remained having taken future dementia into account suggesting that they were not explained by incipient dementia. Additionally, independent measures of executive function accounted for the association between RT metrics and WHM. The results are consistent with the view that frontally-supported cognitive processes are involved in IIV-WMH relations, and that RT measures are sensitive to compromise in white matter structures in non-demented older individuals.

Intraindividual reaction time variability predicts prospective memory failures in older adults

ABSTRACTThis study investigated the relationship between intraindividual variability (IIV) in reaction time and prospective memory errors in older adults using data from the Zurich Longitudinal Study of Cognitive Aging (n = 336 individuals aged 66–81 years). The results indicated that increased IIV measured from independent tasks was associated with a greater proportion of prospective memory errors. These significant findings were not influenced by age and did not vary according to prospective memory cue type. Variability is thought to reflect fluctuations in attentional and executive control and these attentional processes may also impact on prospective memory through failure to detect the target cue. The findings suggest, therefore, that measures of variability may have some potential in the identification of older persons who are more vulnerable to everyday errors such as prospective memory failures.

Mice haploinsufficient for Map2k7, a gene involved in neurodevelopment and risk for schizophrenia, show impaired attention, a vigilance decrement deficit and unstable cognitive processing in an attentional task: impact of minocycline

RationaleMembers of the c-Jun N-terminal kinase (JNK) family of mitogen-activated protein (MAP) kinases, and the upstream kinase MKK7, have all been strongly linked with synaptic plasticity and with the development of the neocortex. However, the impact of disruption of this pathway on cognitive function is unclear.ObjectiveIn the current study, we test the hypothesis that reduced MKK7 expression is sufficient to cause cognitive impairment.MethodsAttentional function in mice haploinsufficient for Map2k7 (Map2k7+/− mice) was investigated using the five-choice serial reaction time task (5-CSRTT).ResultsOnce stable performance had been achieved, Map2k7+/− mice showed a distinctive attentional deficit, in the form of an increased number of missed responses, accompanied by a more pronounced decrement in performance over time and elevated intra-individual reaction time variability. When performance was reassessed after administration of minocycline—a tetracycline antibiotic currently showing promise for the improvement of attentional deficits in patients with schizophrenia—signs of improvement in attentional performance were detected.ConclusionsOverall, Map2k7 haploinsufficiency causes a distinctive pattern of cognitive impairment strongly suggestive of an inability to sustain attention, in accordance with those seen in psychiatric patients carrying out similar tasks. This may be important for understanding the mechanisms of cognitive dysfunction in clinical populations and highlights the possibility of treating some of these deficits with minocycline.

Resting cardiac vagal tone predicts intraindividual reaction time variability during an attention task in a sample of young and healthy adults.

Intraindividual reaction time variability (IIV), defined as the variability in trial-to-trial response times, is thought to serve as an index of central nervous system function. As such, greater IIV reflects both poorer executive brain function and cognitive control, in addition to lapses in attention. Resting-state vagally mediated heart rate variability (vmHRV), a psychophysiological index of self-regulatory abilities, has been linked with executive brain function and cognitive control such that those with greater resting-state vmHRV often perform better on cognitive tasks. However, research has yet to investigate the direct relationship between resting vmHRV and task IIV. The present study sought to examine this relationship in a sample of 104 young and healthy participants who first completed a 5-min resting-baseline period during which resting-state vmHRV was assessed. Participants then completed an attentional (target detection) task, where reaction time, accuracy, and trial-to-trial IIV were obtained. Results showed resting vmHRV to be significantly related to IIV, such that lower resting vmHRV predicted higher IIV on the task, even when controlling for several covariates (including mean reaction time and accuracy). Overall, our results provide further evidence for the link between resting vmHRV and cognitive control, and extend these notions to the domain of lapses in attention, as indexed by IIV. Implications and recommendations for future research on resting vmHRV and cognition are discussed.

Intraindividual Stepping Reaction Time Variability Predicts Falls in Older Adults With Mild Cognitive Impairment.

Reaction time measures have considerable potential to aid neuropsychological assessment in a variety of health care settings. One such measure, the intraindividual reaction time variability (IIV), is of particular interest as it is thought to reflect neurobiological disturbance. IIV is associated with a variety of age-related neurological disorders, as well as gait impairment and future falls in older adults. However, although persons diagnosed with Mild Cognitive Impairment (MCI) are at high risk of falling, the association between IIV and prospective falls is unknown. We conducted a longitudinal cohort study in cognitively intact (n = 271) and MCI (n = 154) community-dwelling adults aged 70-90 years. IIV was assessed through a variety of measures including simple and choice hand reaction time and choice stepping reaction time tasks (CSRT), the latter administered as a single task and also with a secondary working memory task. Logistic regression did not show an association between IIV on the hand-held tasks and falls. Greater IIV in both CSRT tasks, however, did significantly increase the risk of future falls. This effect was specific to the MCI group, with a stronger effect in persons exhibiting gait, posture, or physiological impairment. The findings suggest that increased stepping IIV may indicate compromised neural circuitry involved in executive function, gait, and posture in persons with MCI increasing their risk of falling. IIV measures have potential to assess neurobiological disturbance underlying physical and cognitive dysfunction in old age, and aid fall risk assessment and routine care in community and health care settings.

The Impact of Target Frequency on Intra-Individual Variability in Euthymic Bipolar Disorder: A Comparison of Two Sustained Attention Tasks.

Greater intra-individual variability (IIV) in reaction time (RT) on a sustained attention task has been reported in patients with bipolar disorder (BD) compared with healthy controls. However, it is unclear whether IIV is task specific, or whether it represents general cross-task impairment in BD. This study aimed to investigate whether IIV occurs in sustained attention tasks with different parameters. Twenty-two patients with BD (currently euthymic) and 17 controls completed two sustained attention tasks on different occasions: a low target frequency (~20%) Vigil continuous performance test (CPT) and a high target frequency (~70%) CPT version A-X (CPT-AX). Variability measures (individual standard deviation and coefficient of variation) were calculated per participant, and ex-Gaussian modeling was also applied. This was supplemented by Vincentile analysis to characterize RT distributions. Results indicated that participants (patients and controls) were generally slower and more variable when completing the Vigil CPT compared with CPT-AX. Significant group differences were also observed in the Vigil CPT, with euthymic BD patients being more variable than controls. This result suggests that IIV in BD demonstrates some degree of task specificity. Further research should incorporate analysis of additional RT distributional models (drift diffusion and fast Fourier transform) to fully characterize the pattern of IIV in BD, as well as its relationship to cognitive processes.

Associations between Intra-Individual Variability of Reaction Time and Cognitive Function in Cognitively Normal Senior Adults: Still beyond Good or Bad?

Background: Intra-individual (IIV) of reaction time (RT), as the short-term fluctuations of RT-based performance, has been reported to be susceptible to cognitive ageing. The current study aimed to examine IIV of RT and its relationships with cognitive performance in cognitively normal senior adults. Methods: We evaluated 137 community-dwelling elderly (mean age: 72.41 ± 3.99) with a comprehensive neuropsychological battery and a RT-based test. Intraindividual coefficient of variation of reaction time (ICV-RT) was used to evaluate the IIV. Pearson’s correlation and hierarchical multiple regression analyses were employed to assess the relationships between IIV and the scores of cognitive function. Results: Advancing age was accompanied with declined cognitive function and increased IIV. ICV-RT was negatively correlated with the score of Montreal Cognitive Assessment Hong Kong version (HK MoCA) across three types of flanker. Hierarchical multiple regression showed that ICV-RT was a significant predictor of HK MoCA (β = −0.294, p = 0.001). Conclusion: Increased IIV is consistently associated with and contributed to the age-related decline of cognitive performance in senior adults. The utility of IIV in predicting further deterioration should be carefully postulated with prospective studies.

Mindfulness Training for Older Adults with Subjective Cognitive Decline: Results from a Pilot Randomized Controlled Trial.

Subjective cognitive decline (SCD) in older adults is a condition with a complex phenomenology and diverse etiologies including (but not limited to) mood, personality, and health concerns, as well as biomarkers of preclinical Alzheimer's disease such as amyloid-β deposition and gray matter volume loss. Approximately 60% of affected persons are estimated to decline to Alzheimer's dementia. Regardless of etiology, persons with SCD may be optimal targets for early intervention. To ascertain the feasibility and impact of mindfulness training (MT) as an early intervention in persons with SCD. Using a single-blind, randomized controlled trial design, older adults with (n = 14) and without (n = 22) SCD were randomized to either MT or a control condition of psychoeducation (PE) on cognitive aging. EEG/ERP (specifically, the P3 component), structural MRI, and self-report measures of psychological functioning were obtained within 4 weeks prior to and within 2 weeks following intervention. MT resulted in decreased reaction time intra-individual variability for all participants, with a selective increase in the P3 event-related component for those with SCD. Compared with PE, MT also resulted in an increase in percent volume brain change in structural MRI. Finally, all SCD participants reported a decrease in cognitive complaints and increase in memory self-efficacy following intervention. Results suggest that MT is a feasible early intervention in persons with SCD. Longer-term follow-up with larger sample sizes will determine whether MT can slow the rate of decline in persons who may be at risk for Alzheimer's dementia.

Pretreatment Differences in Intraindividual Variability in Reaction Time between Women Diagnosed with Breast Cancer and Healthy Controls.

Chemotherapy has adverse effects on cognitive performance in women treated for breast cancer, but less is known about the period before chemotherapy. Studies have focused on mean level of performance, yet there is increasing recognition that variability in performance within an individual is also an important behavioral indicator of cognitive functioning and underlying neural integrity. We examined intraindividual variability (IIV) before chemotherapy and surgery in women diagnosed with breast cancer (n=31), and a healthy control group matched on age and education (n=25). IIV was calculated across trials of a computerized Stroop task, including an examination of the slowest and fastest trials of reaction time (RT) responses. The groups were equivalent on overall accuracy and speed, and participants in both groups were less accurate and slower on incongruent trials compared with congruent trials. However, women with breast cancer became more variable with increased task difficulty relative to healthy controls. Among the slowest RT responses, women with breast cancer were significantly more variable than healthy controls on incongruent trials. This suggests that a specific variability-producing process (e.g., attentional lapses) occurs in task conditions that require executive control (e.g., incongruent trials). Results are consistent with other evidence of executive dysfunction among women treated for breast cancer. These findings highlight the importance of pretreatment assessment and show that variability in performance provides information about cognition that measures of central tendency do not.

Amplitude variability over trials in hemodynamic responses in adolescents with ADHD: The role of the anterior default mode network and the non-specific role of the striatum.

It has been suggested that intra-individual variability (IIV) in performance on attention and other cognitive tasks might be a cognitive endophenotype in individuals with ADHD. Despite robust IIV findings in behavioral data, only sparse data exist on how what type of brain dysfunction underlies variable response times. In this study, we asked whether ADHD IIV in reaction time on a commonly-used test of attention might be related to variation in hemodynamic responses (HRs) observed trial-to-trial. Based on previous studies linking IIV to regions within the “default mode” network (DMN), we predicted that adolescents with ADHD would have higher HR variability in the DMN compared with controls, and this in turn would be related to behavioral IIV. We also explored the influence of social anxiety on HR variability in ADHD as means to test whether higher arousal associated with high trait anxiety would affect the neural abnormalities. We assessed single-trial variability of HRs, estimated from fMRI event-related responses elicited during an auditory oddball paradigm in adolescents with ADHD and healthy controls (11–18 years old; N = 46). Adolescents with ADHD had higher HR variability compared with controls in anterior regions of the DMN. This effect was specific to ADHD and not associated with traits of age, IQ and anxiety. However, an ADHD effect of higher HR variability also appeared in a basal ganglia network, but for these brain regions the relationships of HR variability and social anxiety levels were more complex. Performance IIV correlated significantly with variability of HRs in both networks. These results suggest that assessment of trial-to-trial HR variability in ADHD provides information beyond that detectable through analysis of behavioral data and average brain activation levels, revealing specific neural correlates of a possible ADHD IIV endophenotype.

Challenges in the Detection of Working Memory and Attention Decrements among Overweight Adolescent Girls

Background: The present study is unique in employing unusually difficult attention and working memory tasks to reveal subtle cognitive decrements among overweight/obese adolescents. It evaluated novel measures of background electroencephalographic (EEG) activity during one of the tasks and tested correlations of these and other measures with psychological and psychiatric predictors of obesity maintenance or progression. Methods: Working memory and sustained attention tasks were presented to 158 female adolescents who were rated on dichotomous (body mass index percentile <85 vs. ≥85) and continuous (triceps skinfold thickness) measures of adiposity. Results: The results revealed a significant association between excess adiposity and performance errors during the working memory task. During the sustained attention task, overweight/obese adolescents exhibited more EEG frontal beta power as well as greater intraindividual variability in reaction time and beta power across task periods than their normal-weight peers. Secondary analyses showed that frontal beta power during the sustained attention task was positively correlated with anxiety, panic, borderline personality features, drug abuse, and loss of control over food intake. Conclusions: The findings suggest that working memory and sustained attention decrements do exist among overweight/obese adolescent girls. The reliable detection of the decrements may depend on the difficulty of the tasks as well as the manner in which performance and brain activity are measured. Future studies should examine the relevance of these decrements to dietary education efforts and treatment response.