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Biomedical subjects

Adam R Clarke

Publications and source records attributed to Adam R Clarke.

At least 19 recordsLinked to original sources
PubMed2006

EEG abnormalities in adolescent males with AD/HD.

OBJECTIVE: This study investigated EEG abnormalities in adolescents with attention-deficit/hyperactivity disorder (AD/HD). METHODS: Fifteen AD/HD subjects and 15 control subjects participated in this study. All subjects were between 14 and 17 years of age. The EEG was recorded from 19 electrode sites and was analysed to provide estimates of both absolute and relative power in the delta, theta, alpha and beta bands. Theta/alpha and theta/beta ratio coefficients were also calculated. RESULTS: Across the scalp, AD/HD subjects were characterised by greater absolute delta and theta activity, and an increased theta/beta ratio compared to controls. No group differences were found for either absolute or relative alpha, or absolute beta. However, AD/HD subjects demonstrated a reduction in relative beta activity in the posterior regions. CONCLUSIONS: The AD/HD group showed significant deviations from normal CNS development, in particular in posterior regions. This supports previous suggestions that individuals with an EEG profile that is not indicative of a maturational lag are more likely to have AD/HD during adolescence. SIGNIFICANCE: This is the first study to investigate EEG abnormalities in adolescents with AD/HD during an eyes-closed resting condition.

Adolescent↗
PubMed2006

EEG coherence in children with attention-deficit/hyperactivity disorder and comorbid oppositional defiant disorder.

OBJECTIVES: This study is the first to investigate EEG coherence differences between two groups of children with attention-deficit/hyperactivity disorder combined type (AD/HD), with or without comorbid oppositional defiant disorder (ODD), and normal control subjects. METHODS: Each group consisted of 20 males. All subjects were between the ages of 8 and 12 years, and groups were matched on age. EEG was recorded during an eyes-closed resting condition from 21 monopolar derivations. Wave-shape coherence was calculated for 8 intrahemispheric electrode pairs (4 in each hemisphere), and 8 interhemispheric electrode pairs, within each of the delta, theta, alpha, and beta bands. RESULTS: Children with comorbid AD/HD and ODD had intrahemispheric coherences at shorter inter-electrode distances significantly reduced from those apparent in children with AD/HD without comorbid ODD. Such reduced coherences in the comorbid group appeared to wash out coherence elevations previously noted in AD/HD studies. CONCLUSIONS: The present results suggest that, rather than suffering an additional deficit, children with AD/HD and comorbid ODD show significantly less CNS impairment than AD/HD patients without comorbid ODD. SIGNIFICANCE: These results have treatment implications, suggesting that behavioural training, perhaps using family-based cognitive behavioural therapy, could be useful for those children with AD/HD and comorbid ODD. This should focus on the ODD symptoms, in association with a medication regime focussed on the AD/HD symptoms.

Attention Deficit Disorder with Hyperactivity↗
PubMed2006

The development of stop-signal and Go/Nogo response inhibition in children aged 7-12 years: performance and event-related potential indices.

The present study examined the development of response inhibition during the Stop-signal and Go/Nogo tasks in children using performance and ERP measures. Twenty-four children aged 7 to 12 years completed both tasks, each with an auditory Nogo/Stop-signal presented on 30% of trials. On average, response inhibition was more difficult in the Stop-signal than Go/Nogo task. Response inhibition performance did not develop significantly across the age range, while response execution varied significantly in a task dependent manner (Go/Nogo: increasing accuracy and reducing response variability with age; Stop-signal: reducing Go mean reaction time and response variability with age). The N1, P2, N2 and P3 components showed different scalp distributions, with N1 and P2 peaking earlier, and P3 later, in Nogo compared to Stop stimuli. N2 and P3 amplitude were positively correlated with successful inhibition probability in the Go/Nogo task only. N2 amplitude and latency to both Nogo and successful Stop stimuli decreased linearly with age, but not in the frontal regions. N1 and P3 amplitude in the parietal region increased with age for Stop-signals. An age-related reduction in P3 latency to Nogo stimuli correlated significantly with reduced RT and variability in Go responding, indicating a relationship between efficient Nogo and Go processing. Together the behavioural and ERP results suggest little development of the response inhibition process as measured via the Stop-signal and Go/Nogo tasks across the 7 to 12 year age range, while response execution processes develop substantially.

Acoustic Stimulation↗
PubMed2006

Quantitative EEG in low-IQ children with attention-deficit/hyperactivity disorder.

OBJECTIVE: This study investigated EEG differences between children with attention-deficit/hyperactivity disorder (AD/HD) and matched control subjects, with either normal or low IQs. METHODS: Twenty normal-IQ and 20 low-IQ children with AD/HD, and 40 age-, IQ- and sex-matched control subjects participated in this study. EEG was recorded from 21 sites during an eyes-closed resting condition and Fourier transformed to provide estimates for total power, and absolute and relative power in the delta, theta, alpha and beta bands. RESULTS: Children with AD/HD had increased theta activity with decreased levels of alpha and beta activity compared to control subjects. IQ was not found to impact on the EEG. No significant differences were found between subjects with normal and low IQs, with the low- and high-IQ AD/HD groups having similar EEG profiles. CONCLUSIONS: Low-IQ children with AD/HD have similar EEG abnormalities to those with normal IQs, and IQ does not appear to impact on EEG power measures. SIGNIFICANCE: This is the first study to investigate EEG differences in low-IQ children with and without AD/HD.

Adolescent↗
PubMed2006

Inter-modal attention: ERPs to auditory targets in an inter-modal oddball task.

This study investigated ERPs to auditory targets amidst visual standard stimuli in an inter-modal oddball task. Twenty subjects completed three tasks in random order: 1) an inter-modal oddball, 2) an auditory oddball, 3) and a single tone task. Target stimuli were identical in each task. In the inter-modal condition the auditory N100, N130 and P200 components were not substantially affected by the presence of the visual standard stimulus. In contrast, the later components P250, P300 and P350 differed between conditions. It is suggested that the processing of auditory targets in the inter-modal oddball occurs in two-stages--with initial auditory processing occurring independently of the visual standards, followed by activity indicative of an integration of stimulus characteristics. Furthermore, these data indicate that the context in which stimuli are presented affects the ERP. These results are discussed in light of previous findings in inter-modal research.

Acoustic Stimulation↗
PubMed2006

Dynamics of narrow-band EEG phase effects in the passive auditory oddball task.

Evidence suggests that the component frequencies of the electroencephalogram (EEG) are dynamically adjusted to provide particular brain states at stimulus occurrence, and that these facilitate cortical processing of the stimulus. We examined relationships between stimulus intensity, the phase of narrow-band EEG activity at stimulus onset, and the resultant event-related potentials (ERPs) in a passive auditory oddball task, using a novel conceptualization of orthogonal phase effects (cortical negativity vs. positivity, negative driving vs. positive driving, waxing vs. waning). EEG responses to the standard stimuli (50 vs. 80 dB, varied between subjects) were analysed. Prestimulus narrow-band EEG activity (in 1-Hz bands from 1 to 13 Hz) at Cz was assessed for each trial by digital filtering. For each frequency, the cycle at stimulus onset was used to sort trials into four phases, for which ERPs were derived from both the filtered and unfiltered EEG activity at Fz, Cz and Pz. Preferred brain states at various frequencies were indicated by 16-34% differential occurrence within the orthogonal phase dimensions explored. The preferred states were associated with smaller N1, N2 and N3, larger P2 and P3, shorter N1, P2, N2 and P3 latencies, and some intensity effects. These effects reflected the operation of three separate phase-influenced mechanisms, involving anticipatory potentials and prestimulus/poststimulus amplitudes in various EEG frequencies. Results indicate that, even in paradigms with a slightly varying interstimulus interval, brain dynamics provide preferred brain states at the moment of stimulus presentation, which differentially affect the EEG correlates of stimulus processing.

Acoustic Stimulation↗
PubMed2005

Age and gender effects in EEG coherence: III. Girls with attention-deficit/hyperactivity disorder.

OBJECTIVE: This study investigated intrahemispheric and interhemispheric EEG coherences as a function of age in girls with different DSM-IV subtypes of Attention-Deficit/Hyperactivity Disorder (AD/HD). It completes a series of 3 studies aimed at clarifying developmental and gender impacts on the coupling between brain regions in this disorder. METHODS: Three groups of 40 children (AD/HD combined type, AD/HD inattentive type, and normal controls) participated. Each group contained 8 females in each of 5, 1-year age bands from 8 to 12 years. EEG was recorded from 21 sites during an eyes-closed resting condition. Wave-shape coherence was calculated for 8 intrahemispheric electrode pairs (4 in each hemisphere), and 8 interhemispheric electrode pairs, within each of the delta, theta, alpha and beta bands. RESULTS: Developmental effects in intrahemispheric coherences at shorter and longer inter-electrode distances were not as predicted by Thatcher's two-compartment model, contrary to previous findings in boys. Females with AD/HD showed evidence of developmental delay and widespread anomalous elevations in coherence. Girls with AD/HD of the combined type showed similar but greater anomalies than girls with AD/HD of the inattentive type. CONCLUSIONS: Girls with AD/HD show coherence anomalies relative to age- and gender-matched controls, which differ substantially from those shown by boys with AD/HD. These coherence anomalies did not differ in nature between girls with different DSM-IV subtypes of AD/HD, suggesting that subtype differences in girls reflect only symptom severity. SIGNIFICANCE: The data reported here indicate qualitative differences in EEG coherences in girls with AD/HD compared with controls, and quantitative differences between girls with different subtypes of AD/HD. Both sets of effects differ in nature from those previously found in boys with AD/HD, showing the need to carefully consider gender in future studies of AD/HD.

Aging↗
PubMed2005

Quantitative EEG analysis in dexamphetamine-responsive adults with attention-deficit/hyperactivity disorder.

Attention-deficit/hyperactivity disorder (AD/HD) is recognized as a disorder affecting children and adolescents and has more recently been documented to continue into adulthood in a proportion of patients. One of the common treatments for AD/HD is the use of stimulant medications. Numerous studies have examined the therapeutic effects of stimulant medications in children, adolescents and adults with the disorder, reporting improvements in attention, concentration, and hyperactive and impulsive behaviours. Several studies have also examined the effects of stimulants on the electroencephalograph (EEG) of children and adolescents with the disorder, but to date, there have been no studies examining the effects of stimulant medication on the EEG of adults with AD/HD. In the present study, we aimed to replicate previous EEG findings in adults with AD/HD relative to controls and to examine whether there was any change in this profile following treatment with dexamphetamine. The EEG was recorded at rest in an eyes-open condition from 50 adults diagnosed with AD/HD and assessed as good responders to treatment, both before and after treatment with dexamphetamine, and 50 control subjects. The pre-medication results are similar to those found in previous research that compared the EEGs of adults with AD/HD and control subjects. Following medication, there was a significant reduction in slow wave activity in the AD/HD group to levels similar to those in the control group. These results suggest that changes in brain function of good responders to dexamphetamine, as reflected in the EEG, may underlie the behavioural improvements observed in the clinical setting.

Adult↗
PubMed2005

Methylphenidate effects in attention deficit/hyperactivity disorder: electrodermal and ERP measures during a continuous performance task.

RATIONALE: Previous research investigating the effects of stimulants, such as methylphenidate (MPH), on children with attention deficit/hyperactivity disorder (AD/HD) has rarely included autonomic measures of arousal. OBJECTIVE: Our aim was to clarify the effects of MPH on central and autonomic measures in AD/HD children during a continuous performance task (CPT) using a naturalistic open-label study. METHOD: Thirty-six boys (18 AD/HD and 18 control) participated in a CPT over two trial periods, allowing a more valid estimate of the effects of medication, rather than assuming that retesting per se has no substantial impact. MPH was administered to the AD/HD group 1 h prior to the second trial. Errors and reaction time (RT) were recorded as measures of performance, electrodermal activity as an autonomic nervous system measure and event-related potentials (ERPs) as an index of central nervous system activity. RESULTS: AD/HD children made more errors than controls in the first session, but no group differences were found after medication. No significant differences were observed for RT. Skin conductance level was found to be lower in AD/HD children than controls, but this difference was also ameliorated after medication. Conversely, mean skin conductance response to target stimuli was found not to differ between groups during the initial test phase but became significantly different in phase 2. ERP data showed topographic differences between groups in N1, P2, N2 and P3 at the initial test phase, which were reduced at the second test. CONCLUSION: Stimulant medication ameliorated some of the dysfunctions in AD/HD children, which are reflected in behavioural and ERP measures. These results, in combination with general differences in electrodermal activity, support a hypo-arousal model of AD/HD, which can explain the action of MPH in these children.

Adolescent↗
PubMed2005

Caffeine effects on resting-state arousal.

OBJECTIVE: This study examined the use of caffeine to manipulate arousal level without the confounds associated with task-related activation. From previous work in our laboratory, an increase in skin conductance level (SCL) and EEG alpha frequency, together with a global decrease in alpha power, were used as markers of arousal increase, and we sought to identify these effects with caffeine ingestion. METHODS: We examined the effect of a single oral dose of caffeine (250 mg) in a randomised double-blind placebo-controlled repeated-measures cross-over study. Eighteen healthy university students (mean age 21 years; 13/18 females) participated in two sessions 1 week apart. EEG and autonomic data (SCL, heart rate, systolic and diastolic blood pressure, and respiration rate) from a 2 min eyes-closed epoch, commencing approximately 30 min after ingestion of caffeine or placebo, were examined. RESULTS: Caffeine was associated with increased SCL, a global reduction in EEG power in the alpha band, and a global increase in alpha frequency. There were no cardiovascular effects. CONCLUSIONS: The positive results are consistent with recent electrodermal and EEG studies of arousal and suggest that caffeine may be utilised as a task-free means of manipulating arousal in future investigations. Further work is necessary to clarify the absence of cardiovascular effects, and to integrate those data with emerging conceptualisations of arousal and activation. SIGNIFICANCE: The present data support the use of caffeine as a simple tool to explore the role of arousal in both normal and atypical functioning, and this may be useful in determining the validity and importance of supposed hyper- or hypo-arousal in such syndromes as attention-deficit/hyperactivity disorder (AD/HD).

Adult↗
PubMed2005

Examining the diagnostic utility of EEG power measures in children with attention deficit/hyperactivity disorder.

OBJECTIVE: This study investigated the diagnostic utility of EEG power during eyes-closed resting conditions for children with attention-deficit/hyperactivity disorder (AD/HD). METHODS: Subjects consisted of 253 boys with AD/HD combined type and 67 age-matched controls. EEG was recorded from 21 sites during an eyes-closed resting condition and was Fourier transformed to provide estimates for total power and absolute and relative power in delta, theta, alpha and beta bands. Factor analysis was used to group sites into frontal, central and posterior regions, with these data subjected to cluster analysis. Logistic regression was performed on the entire AD/HD sample versus control, for AD/HD clusters versus control, and then for each AD/HD cluster independently versus control, using total, absolute and relative power measures. RESULTS: Logistic regression performed on the clusters independently produced the best classification results, with a sensitivity of 89.0% and a specificity of 79.6%, with an overall classification accuracy of 87.0%. CONCLUSIONS: The obtained classification results are supportive of an independent diagnostic test for AD/HD based on EEG power at rest. SIGNIFICANCE: This is the first study to investigate sensitivity and specificity of EEG power for AD/HD in a resting condition.

Adolescent↗
PubMed2005

Behavioral aspects of Angelman syndrome: a case control study.

Angelman syndrome (AS) is a rare congenital disorder characterized by impairments in intellectual, neurological and motor functioning and a postulated behavioral profile. This study compared behavioral characteristics of 62 individuals with genetically confirmed AS and 29 individuals with presumed AS from clinical features, with a control group of young persons with intellectual disability (ID) derived from an Australian epidemiological register. Twelve behavioral items from the developmental behavior checklist (DBC) were used for this comparison. The groups were matched for chronological age, gender, and level of ID. In the AS group, significant differences were found for 10 behaviors, with poor attention span and impulsivity being less common, and overactivity/restlessness, chewing or mouthing objects, eating non-food items, gorging food, food fads, fascination for water, hand flapping and sleep disturbance being more common. Interestingly, there was no difference in prevalence of unprovoked laughter. Comparison of the results of the genetically confirmed with the genetically unconfirmed AS cases showed no significant differences between individual behavior prevalence. These findings show that a "behavioral phenotype" of AS can be distinguished from others of similar level of ID, but it is different from that hitherto published. Abnormal food related behaviors, hyperactivity, fascination for water, hand flapping, and sleep disturbance should be included in a "behavioral phenotype" for AS. Apart from hyperactivity, "ADHD-type" behaviors are not more characteristic of AS than in ID generally. Therefore, the Consensus Criteria for the diagnosis of AS need to be reviewed.

Adolescent↗
PubMed2005

Adjusting EEG coherence for inter-electrode distance effects: an exploration in normal children.

Electroencephalographic (EEG) coherence between two points is strongly related to the distance between them, being inflated by volume conduction effects at short distances and reduced by signal phase differences at larger distances. This precludes simple comparison of coherence estimates involving different inter-electrode distances. We investigated adjusting coherence measures to remove such distance effects. After subtracting the estimated effects of random coherence due to volume conduction, exponential regression of the reduced coherence values against measured inter-electrode distance was used to estimate the remaining effects of inter-electrode distance. Residuals from this procedure were taken as coherences corrected for the systematic distance effects. These were adjusted to the mean reduced coherence level to avoid complexities in conceptualising negative residual coherences. It was found that systematic inter-electrode distance effects accounted for more than 50% of the variance remaining after removal of random coherence estimates. After these were also removed, substantial effects of EEG frequency band, different regions of the brain, and interhemispheric versus intrahemispheric values, as well as laterality effects within the latter, were obtained. Regional and frequency differences in adjusted coherence appear to reflect patterns expected from normal cortical development, but detailed understanding of more complex interactive effects is limited by the lack of relevant developmental data. Adjusting coherence values to remove systematic variability due to inter-electrode distances better represents cortico-cortical coupling and allows more efficient statistical analysis. This may contribute towards a better integration of coherence data in the EEG exploration of both normal and atypical brain functioning.

Brain↗
PubMed2005

Effects of methylphenidate on EEG coherence in attention-deficit/hyperactivity disorder.

This study investigated the effects of methylphenidate on intrahemispheric and interhemispheric EEG coherence in children with Attention-Deficit/Hyperactivity Disorder (AD/HD). Twenty boys with AD/HD Combined type and 20 age- and sex-matched control subjects, aged 8 to 13 years, participated in this study. EEG was recorded from 21 sites during an eyes-closed resting condition. Wave-shape coherence was calculated for eight intrahemispheric electrode pairs (four in each hemisphere), and eight interhemispheric electrode pairs, within each of the delta, theta, alpha and beta bands. AD/HD children were tested both off and, 6 months later, on a therapeutic dose of methylphenidate. In intrahemispheric comparisons, AD/HD children had lower theta coherences at long inter-electrode distances, and reduced lateralisation at both long and short-medium inter-electrode distances than controls. For interhemispheric comparisons, AD/HD children showed increased coherences in the frontal regions for the low frequency bands (delta and theta), and reduced coherences in the alpha bands in all other regions. These EEG coherences suggest reduced cortical differentiation and specialisation in AD/HD, particularly in the frontal regions. Methylphenidate did not produce any changes in coherence values. The lack of sensitivity of coherence measures to methylphenidate in the present study suggests that eyes-closed resting EEG coherence measures are associated with structural connectivity of the underlying regions of the brain rather than the degree of functionality of these regions. These results suggest the existence of structural as well as functional brain dysfunction in AD/HD.

Adolescent↗
PubMed2005

EEG coherence adjusted for inter-electrode distance in children with attention-deficit/hyperactivity disorder.

Cognition and behaviour depend on the integration of activity in different brain regions, and hence study of the coupling between regions is useful in understanding dysfunctional processes involved in disorders such as attention-deficit/hyperactivity disorder (AD/HD). Such coupling can be estimated by the electroencephalographic (EEG) coherence between scalp electrodes. However, EEG coherence between two points is strongly affected by the distance between them, being inflated by volume conduction effects at short distances and reduced by signal phase differences at larger distances. These distance effects preclude simple comparison of coherence estimates involving different inter-electrode distances. Our group recently introduced a procedure for adjusting coherence measures to remove such distance effects, and explored its potential using normal children. In this study we applied that coherence adjustment procedure to groups of children with AD/HD of the combined (AD/HDcom) and predominantly inattentive (AD/HDin) subtypes, and compared them with a control group. All groups were age- and gender-matched. AD/HD children were found to have a reciprocal pattern of coherence disturbance in the cortico-cortical circuits involved in slow and fast wave activity-elevated slow-wave coherences and reduced fast-wave coherences. This disturbance was larger for inter-hemispheric than intra-hemispheric coherences, and varied markedly with region, suggesting a complex pattern of coherence anomalies with a substantial frontal focus. This complex pattern differed little between subtypes, suggesting that it may constitute the fundamental dysfunction underlying the inattention common to both groups. In contrast, coherence was globally elevated in children with AD/HDcom compared with both AD/HDin and control children. This elevation in coherence may be directly related to the hyperactivity and impulsivity unique to that subtype. Further research using the coherence adjustment procedure appears useful in elucidating the electrophysiological anomalies underlying AD/HD and other disorders.

Attention Deficit Disorder with Hyperactivity↗