Electrophysiology and intelligence.
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Cognition↗
Biomedical subjects
Robert J Barry
Publications and source records attributed to Robert J Barry.
Separation of the components of the late positive complex in an ERP dishabituation paradigm.
OBJECTIVE: A substantial body of evidence shows that several separate components underlie the late positive complex (LPC) of the ERP. Each of these has been proposed as a possible neural index of the orienting reflex (OR), but none has clearly met the criteria required for identification as an OR. The skin conductance response (SCR) is the most extensively examined index of the OR, and was used here as an OR 'yard-stick'. The primary aim of this study was to determine if any of the components of the LPC show stimulus-response relationships analogous to those of the SCR. METHODS: ERPs and SCRs were simultaneously recorded from 72 subjects during an ERP dishabituation paradigm, in which a habituation stimulus (S1) was presented for a series of trials, during which a different stimulus (S2) was interpolated. This sequence was presented in a series of trains, allowing across-train LPC and SCR exploration as a function of trial. The sensitivity of these components to stimulus intensity and significance, other stimulus dimensions important in defining the OR, was also examined. We utilised a PCA with varimax rotation to separate the ERP components underlying the LPC. RESULTS: Four factors extracted appeared to correspond to the classic Slow Wave, the P3b, the Novelty P3 and the P3a. While the LPC exhibited a stimulus-response relationship analogous to the SCR, each of the separate components was differentially sensitive to aspects of the stimulus manipulations examined here. CONCLUSIONS: This study has demonstrated that the LPC is an adequate EEG index of the OR. However, the underlying components of the LPC examined here--which we consider to be the classic slow wave, P3b, Novelty P3 and P3a--cannot be used interchangeably as OR indices. SIGNIFICANCE: This study clarifies links between the autonomic OR and its CNS correlates.
Acoustic Stimulation↗
Sensitivity of primary phasic heart rate deceleration to stimulus repetition in an habituation procedure: influence of a subjective measure of activation/arousal on the evoked cardiac response.
The post-stimulus primary bradycardia--sometimes labelled as the first evoked cardiac response, ECR1--is regarded as a response which is independent of the stimulus novelty factor. Despite this however, in our previous research we have observed a noticeable variation of this response, which made us suspect that there could be some additional factor influencing it. To test this, we designed a habituation procedure to measure susceptibility of the ECR1 to stimulus repetition. In our experimental design, we also included a measure of the level of activation (arousal) as a possible additional factor influencing the time-course of the cardiac response. The level of arousal over the study was measured by the Activation-Deactivation Adjective Check List (AD ACL). Our results show that mere stimulus repetition does not influence the time-course of ECR1. However, another pattern of results appeared when one of the dimensions of AD ACL, namely Tense Arousal, was taken into account. We observed different ECR time-courses during the initial stimulus presentations for subjects with high and low levels of Tense Arousal. These results are interpreted within the framework of Preliminary Process Theory in terms of the different attentional patterns in subjects with high and low levels of Tense Arousal.
Acoustic Stimulation↗
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↗
Electrophysiology in attention-deficit/hyperactivity disorder.
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Attention Deficit Disorder with Hyperactivity↗
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↗
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↗
The effect of methylphenidate on response inhibition and the event-related potential of children with attention deficit/hyperactivity disorder.
Children with Attention Deficit/Hyperactivity Disorder (AD/HD) appear to be deficient in inhibitory processes, as reflected in behavioural and electrophysiological measures. This study examined the effect of methylphenidate (MPH) on response inhibition in children with AD/HD. Event-related potentials (ERPs) and skin conductance level (SCL) were recorded from 18 boys with AD/HD and 18 controls while they performed a cued Go/Nogo task with 70% Go probability. All participants performed the task twice, with an hour interval between test sessions. At the beginning of this interval children with AD/HD took their normal morning dose of MPH. The AD/HD group showed lower SCL than controls pre-medication, a difference not found subsequent to the administration of MPH. While the AD/HD group made more overall errors (omission+commission) pre-medication, and continued to make more omission errors than controls post-medication, the groups became comparable on the number of commission errors, suggesting MPH ameliorates deficits in response inhibition. Children with AD/HD displayed enhanced N1 and P2 amplitudes, and reduced N2 amplitudes relative to controls. These differences were not significant post-medication, at least partly attributable to the action of MPH. This study is unusual in the concurrent examination of electrodermal and electrophysiological measures of medication effects in children with AD/HD, with the retesting of both the AD/HD and control groups allowing a more valid estimate of the effects of medication, rather than assuming that retesting does not have a substantial impact.
Adolescent↗
Event-related potentials in attention-deficit/hyperactivity disorder of the predominantly inattentive type: an investigation of EEG-defined subtypes.
Research using resting EEG measures suggests that there is a large variability in EEG profiles within the common behaviourally defined DSM-IV subtypes of AD/HD. Within the predominantly inattentive type of AD/HD (AD/HDin), two distinct groups have been identified, based on underlying EEG activity that represents either cortical hypoarousal, or a maturational lag (with EEGs resembling those of younger children). This study investigated whether ERPs from an inter-modal oddball task could differentiate AD/HDin children from controls, and whether the ERPs of the two previously identified subgroups of AD/HDin children with different EEG profiles differ on this task. AD/HDin children (N=54), 27 identified as cortically hypoaroused and 27 as maturationally lagged, and 27 age-matched controls, were presented with an inter-modal oddball task in which the non-target stimulus was a counter-phasing checkerboard and the target was a 2000 Hz auditory tone. Stimuli (20% targets) were presented at a fixed ISI of 1.03 s and participants were required to count all targets. The task successfully differentiated the AD/HDin children from controls, with AD/HDin children having smaller N1, P2 and P3 amplitudes to both the auditory targets and the visual non-targets. These results were interpreted as indicating a generalised stimulus registration, facilitation and processing deficit in AD/HDin. The only difference between the EEG-defined subtypes was a relative increase in left-frontal N1 amplitude in the cortically hypoaroused group. This was interpreted as indicating reduced frontal lateralisation of N1 in the maturational lag group, supporting its labelling, and anomalous lateralisation in the cortical hypoarousal group.
Arousal↗
EOG correction: a comparison of four methods.
EOG correction is a class of techniques that account for ocular artifact in the electroencephalogram (EEG) by subtracting electrooculographic data from the EEG. The purpose of this study was to evaluate four of these correction techniques (Verleger, Gasser, & Mocks, 1982 [VGM]; Gratton, Coles, & Donchin, 1983 [GCD]; Semlitsch, Presslich, Schuster, & Anderer, 1986 [SPSA]; Croft & Barry, 2000 [CB]). Blinks, vertical eye movements (VEM), and horizontal eye movements (HEM) from 26 subjects were corrected using these techniques, and eye movement event-related potentials computed to aid validation. HEMs were corrected better by CB, VGM/GCD then SPSA, VEMs by CB, VGM/GCD then SPSA, and blinks by CB, SPSA, GCD and then VGM, with the advantage of CB substantial for blinks (eta2>.72), VEMs (eta2>.60), and HEMs (eta2>.27). It is argued that the CB procedure adequately accounts for ocular artifact in the EEG. Reasons for the limitations of the other procedures are discussed.
Blinking↗
Age and gender effects in EEG coherence: II. Boys with attention deficit/hyperactivity disorder.
OBJECTIVE: This study investigated intra-hemispheric and inter-hemispheric EEG coherences as a function of age in boys with different subtypes of Attention Deficit/Hyperactivity Disorder (AD/HD), in comparison with a control group of normal boys. METHODS: Three groups of 40 children (AD/HD combined type, AD/HD inattentive type, and normal controls) participated. Each group contained 8 males in each 1 year band from 8 to 12 years. EEG was recorded from 21 sites during an eyes-closed resting condition. Wave-shape coherence was calculated for 8 intra-hemispheric electrode pairs (4 in each hemisphere), and 8 inter-hemispheric electrode pairs, within each of the delta, theta, alpha and beta bands. RESULTS: Developmental effects in intra-hemispheric coherences at shorter and longer inter-electrode distances generally supported Thatcher's two-compartment model. Control boys showed evidence of development in longer-range inter-hemispheric coherences which was not apparent in AD/HD boys. Boys with AD/HD of the combined type showed qualitatively different anomalies than boys with AD/HD of the inattentive type. CONCLUSIONS: EEG coherences in normal boys of this age range develop systematically with age in a non-linear fashion. Boys with AD/HD do not show this development. They display coherence anomalies which differ in nature between DSM-IV subtypes, suggesting differences which are not relatable to simple symptom severity. SIGNIFICANCE: The data reported here indicate differences in the development of EEG coherences in boys with AD/HD, and point to differences between the AD/HD subtypes which may help understanding of the disorder.
Age Factors↗
Inhibitory processing during the Go/NoGo task: an ERP analysis of children with attention-deficit/hyperactivity disorder.
OBJECTIVE: Previous event-related potential (ERP) research on inhibitory functioning in attention-deficit/hyperactivity disorder (AD/HD) has often failed to use tasks which optimally assess inhibition. We report on an improved measure of inhibitory function, involving inhibition of a prepotent response, in children with AD/HD. METHODS: Twelve males with AD/HD and 12 control males, aged 7-12 years, completed a cued Go/NoGo task where Go stimuli were presented on 70% of trials. ERP and behavioural measures were collected, together with reading, spelling and full-scale IQ scores. RESULTS: The behavioural performance of children with AD/HD was not significantly different from normal controls, although children with AD/HD made faster responses and more errors. Group differences were apparent in the early processing components (P1, N1, P2) of responses to Warning, Go and NoGo stimuli. For the frontally maximal N2, a NoGo>Go effect was found, consistent with previous work linking this component with inhibitory processing. In control children this effect was particularly strong in the right frontal region, while children with AD/HD showed a much larger NoGo>Go effect, and an earlier N2 peak, than controls, with a focal shift to the left frontal region. CONCLUSIONS: Compared with normal controls, children with AD/HD demonstrate early stimulus processing atypicalities, suggesting problems with sensory registration and identification of stimuli. Further, N2 results suggest that children with AD/HD must trigger the inhibition process earlier and more strongly than controls to perform at a comparable behavioural level. SIGNIFICANCE: The results support the theory that behavioural inhibition is deficient in AD/HD, as children with AD/HD show abnormalities in inhibitory ERP components relating to the effort involved in inhibiting a prepotent response.
Attention Deficit Disorder with Hyperactivity↗
Age and gender effects in EEG coherence: I. Developmental trends in normal children.
OBJECTIVE: This study investigated intra-hemispheric and inter-hemispheric EEG coherences as a function of age and gender in normal children. METHODS: Two groups of 40 boys and 40 girls, each containing 8 normal children in each 1-year band from 8 to 12 years, participated. EEG was recorded from 21 sites during an eyes-closed resting condition. Wave-shape coherence was calculated for 8 intra-hemispheric electrode pairs (4 in each hemisphere), and 8 inter-hemispheric electrode pairs, within each of the delta, theta, alpha and beta bands. RESULTS: There was consistent evidence of coherences developing across this age range, particularly in long-range intra- and inter-hemispheric electrode pairs. Coherences were larger in the left hemisphere than the right. Coherences also appeared to develop further in males than females, across several regions and frequency bands, suggesting that females lag males in this aspect of brain development. CONCLUSIONS: EEG coherences in normal children of this age range develop systematically with age. These developmental effects vary substantially with gender, brain region and frequency bands. SIGNIFICANCE: The data reported here provide basic norms for coherence development in different brain regions in normal children.
Aging↗
Event-related potentials in the auditory oddball as a function of EEG alpha phase at stimulus onset.
OBJECTIVE: We aimed to examine the relation between the phase of electroencephalogram (EEG) alpha activity at stimulus onset and event-related potentials (ERPs) in a fixed-inter-stimulus interval auditory 'oddball' task, using a novel conceptualisation of orthogonal phase effects (cortical negativity versus positivity, negative driving versus positive driving, waxing versus waning). METHODS: EEG responses to button-press targets, from 14 subjects presented with 4 blocks of 150 stimuli (50% target probability), were examined. Pre-stimulus alpha activity (8-13 Hz) at Pz was assessed for each trial by digital filtering of the EEG. The alpha cycle at Pz, starting from a negative-going zero crossing, was used to sort trials into 4 phases, for which ERPs were derived from both the filtered and unfiltered EEG activity at Fz, Cz, and Pz. RESULTS: Preferred brain states in this paradigm were indicated by an 8% greater occurrence of negative driving than positive driving, and a 33% greater occurrence of waxing than waning phases. Negative driving phases were associated with increased N1 latencies and decreased N2 amplitudes. Latencies of N1 and P2 were reduced in waxing phases. These reflected systematic changes in alpha frequency and amplitude at stimulus onset. CONCLUSIONS: In a fixed-inter-stimulus interval paradigm, component frequencies of the EEG are dynamically adjusted in order to provide brain states at the moment of stimulus presentation which differentially affect the EEG correlates of stimulus processing. SIGNIFICANCE: The results add to our understanding of the genesis of the ERP, indicating the importance of the dynamic interplay between instantaneous EEG activity and stimulus processing reflected in the ERP.
Acoustic Stimulation↗
Differential relations between heart rate and skin conductance, and public speaking anxiety.
The present pilot study tested whether the lack of consistent findings of relations between autonomic nervous system (ANS) activity and non-clinical levels of public speaking anxiety (PSA) can be explained by methodology. An ambulatory protocol was utilised to test whether the interaction of belief structure with each of an undergraduate student speaker's heart rate and skin conductance level predicted state speech anxiety better than their linear summation. Results suggest that in a non-clinical population, the interaction of ANS activity and belief structure is an important determinant of PSA, and may account for variable findings in the literature.
Adult↗
EEG differences in children as a function of resting-state arousal level.
OBJECTIVE: This study aimed to explore the basis of a theoretical position which has major impact in the current literature on attention-deficit/hyperactivity disorder (AD/HD) - that the ratio of theta to beta power in the EEG (the theta/beta ratio) represents central nervous system (CNS) arousal. METHODS: Resting state topographic EEG activity was investigated as a function of CNS arousal in normal right-handed boys. Arousal was defined in terms of electrodermal activity, which has a long history in Psychology as a measure of CNS arousal. RESULTS: Relative delta, theta, and beta power, and the theta/beta ratio, failed to differ significantly between age-matched groups which differed markedly in skin conductance level and non-specific electrodermal fluctuations. The high-arousal group showed significantly lower levels of relative alpha power, particularly in posterior and hemispheric regions, with higher alpha frequencies in these areas. CONCLUSIONS: These data fail to support the theoretical linkage between the theta/beta ratio and CNS arousal. Further work is needed to disentangle the different correlates of arousal and task-related activation, particularly in cognitive and attentional-processing terms. SIGNIFICANCE: The outcomes of this study, in addition to clarifying the nature of EEG markers of CNS arousal, have important implications for our understanding of AD/HD, as they require re-evaluation of current models of the disorder.
Analysis of Variance↗
Inhibitory motor control in children with attention-deficit/hyperactivity disorder: event-related potentials in the stop-signal paradigm.
BACKGROUND: The aim of the study was to investigate the inhibitory control of an ongoing motor response and to identify underlying neural deficiencies, manifested in event-related potentials, that cause poorer inhibitory performance in children with attention-deficit/hyperactivity disorder. METHODS: A stop-signal paradigm with a primary visual task and auditory stop signal was used to compare performance in 13 children with attention-deficit/hyperactivity disorder and 13 control children, while event-related potentials were recorded simultaneously. RESULTS: Children with attention-deficit/hyperactivity disorder showed poorer inhibitory performance through a slower inhibitory process. Inhibitory processing of auditory stop signals was marked by a frontal N2 component that was reduced in the attention-deficit/hyperactivity disorder group relative to controls. A central positive component (P3) was associated with the success of inhibiting a response, but there were no group differences in its amplitude or latency. CONCLUSIONS: Findings support the hypothesis of deficient inhibitory control in children with attention-deficit/hyperactivity disorder. Slower inhibitory processing appears to be due to a specific neural deficiency that manifests in the processing of the stop signal as attenuated negativity in the N2 latency range.
Acoustic Stimulation↗
Effects of stimulant medications on the EEG of children with Attention-Deficit/Hyperactivity Disorder Predominantly Inattentive type.
Stimulant medications are the most commonly-used treatments for Attention-Deficit/Hyperactivity Disorder (ADHD) in North America and Australia, although it is still not entirely known how these medications work. This study investigated the effects of stimulant medications on the EEG of children with the Inattentive type of ADHD. An initial EEG was recorded during an eyes-closed resting condition and Fourier transformed to provide absolute and relative power estimates for the delta, theta, alpha and beta bands. Theta/alpha and theta/beta ratios were also calculated. Subjects were placed on a 6-month trial of a stimulant and a second EEG was recorded at the end of the trial. Subjects were included in this study only if they showed a good clinical response during the trial. The unmedicated ADHD group had significantly greater absolute and relative theta, less relative alpha, and higher theta/alpha and theta/beta ratios than the control group. The stimulant medications resulted in a normalisation of the EEG, with changes in the theta, alpha and beta bands being most evident. These results suggest that stimulants act to increase cortical arousal in children with ADHD, normalising their EEG.
Adolescent↗