Biomedical subjects

R J Barry

Publications and source records attributed to R J Barry.

At least 19 recordsLinked to original sources

PubMed2001

Excess beta activity in children with attention-deficit/hyperactivity disorder: an atypical electrophysiological group.

Studies of children with attention deficit/hyperactivity disorder (ADHD) have typically found elevated levels of slow wave activity in their EEGs, but in two of our previous studies, a small subset of ADHD children with excess beta activity in the EEG was identified. The aim of this study was to determine whether children with excess beta activity represent a distinct electrophysiological subtype of ADHD, to quantify the differences in their EEGs, and to determine if this group of children with ADHD have behavioural profiles different from other children with ADHD. Results indicated that children with excess beta represent a small independent subset of children diagnosed with ADHD, which primarily consists of children with a diagnosis of ADHD combined type. Behaviourally, this group was similar to other children with ADHD, although the excess-beta group were more prone to temper tantrums and to be moody. The excess in beta activity was found primarily in the frontal regions and may be associated with frontal lobe self-regulation and inhibition control.

Attention Deficit Disorder with Hyperactivity↗

PubMed2001

Elite pistol shooters: physiological patterning of best vs. worst shots.

This study examined patterns of physiological activity in elite pistol shooters and compared them with novice shooters. Heart rate and electrodermal activity were recorded for three 150-s epochs. Participants performed part of the Standard Pistol Shooting Protocol, firing five rounds at a target 25 m distant within the first 150 s epoch. In the second epoch, baseline data were recorded with the participant standing at rest. The third epoch was a repetition of the first epoch. For each shot, values of heart rate and skin conductance were calculated at half-second intervals from 20 s before to 10 s after the shot. In experts there was a slow reduction in skin conductance and heart rate levels prior to the shot, and a 'rebound' increase immediately following the shot, which were not apparent in the novice shooters. Pre-shot electrodermal levels for the expert shooters were lower for the best compared with the worst shots, and the duration of the pre-shot cardiac deceleration was longer and more systematic for best than for worst shots. The physiological profiles supported interpretation in terms of two separate state processes, arousal and vigilance, rather than a single construct. These physiological differences are discussed in terms of differential engagement with the task and its associated attentional narrowing in expert pistol shooters.

Adolescent↗

PubMed2001

Topographic distribution and developmental timecourse of auditory event-related potentials in two subtypes of attention-deficit hyperactivity disorder.

The effect of age on the topographic distribution of auditory event-related potentials (ERPs) recorded during a two-tone discrimination, or oddball, task was examined in two subtypes of attention deficit/hyperactivity disorder (AD/HD) as defined by the most recent diagnostic manual, DSM-IV. EEG was recorded at 17 sites from AD/HD predominantly inattentive type (n=50) and AD/HD combined type (n=50) subjects aged from 8 to 17 years 11 months. ERP components were quantified at each site. Results revealed topographic differences from controls (n=50) that were common to both subtypes (e.g. target and standard P2 amplitude, and standard P2 latency) or unique to a particular subtype of AD/HD (Inattentive type: target N1, N2, P3b and standard N2 amplitude, target P2 latency; Combined type: target N1, P2, N2 and P3b amplitude, target N2 and standard N1 latency). These group differences showed different age effects. The across-region results revealed differing patterns of abnormal component development for each subtype, indicating a qualitative difference in information processing stage deficits in each of these AD/HD subtypes.

Acoustic Stimulation↗

PubMed2001

Age and sex effects in the EEG: differences in two subtypes of attention-deficit/hyperactivity disorder.

OBJECTIVES: This study investigated age-related changes and sex differences in the EEGs of two groups of children with attention-deficit/hyperactivity disorder (ADHD) combined type and ADHD predominantly inattentive type, in comparison with a control group of normal children. METHODS: Forty boys and forty girls were included in each group. The EEG was recorded during an eyes-closed resting condition and Fourier transformed to provide estimates for total power, absolute and relative power in the delta, theta, alpha and beta bands, and for theta/alpha and theta/beta ratios. RESULTS: Total power, relative alpha, and the theta/alpha and theta/beta ratios were differentiated between all 3 groups. Sex differences between the ADHD subjects and the control group were greater in males than females and matured faster in males. With increasing age, the EEG of the ADHD inattentive group was found to change at a similar rate to the changes found in the normal group, with the differences in power levels remaining constant. In the ADHD combined group, the power was found to change at a greater rate than in the ADHD inattentive group, with power levels of the two ADHD groups becoming similar with age. CONCLUSIONS: These results are supportive of a two-component model of ADHD, with the hyperactive/impulsive component maturing with age and the inattentive component remaining more stable.

Aging↗

PubMed2001

Age and sex effects in the EEG: development of the normal child.

OBJECTIVES: This study investigated age-related changes and sex differences in the EEGs of normal children. METHODS: Forty boys and 40 girls, between the ages of 8 and 12 years, participated in this study. The EEG was recorded during an eyes-closed resting condition and Fourier transformed to provide estimates for total power, absolute and relative power in the delta, theta, alpha and beta bands, and for theta/alpha and theta/beta ratios. RESULTS: Absolute delta activity decreased with age. Relative delta and theta decreased and alpha and beta increased with increasing age. The theta/alpha and theta/beta ratios decreased with increasing age. All of these indicated a developmental reduction in slow wave activity. Maturational differences were found in the rates of change between the midline and the two hemispheres. In the absolute delta and the theta/beta ratio, the midline and the two hemispheres became more equipotential with age. In the beta band, power increased at a greater rate than in the two hemispheres. Sex differences were found, with males having less theta and more alpha than females. CONCLUSIONS: These results indicated that maturation occurs earlier at the midline than in the two hemispheres. Females were also found to have a developmental lag in the EEG compared with males.

Age Factors↗

PubMed2001

Electroencephalogram differences in two subtypes of attention-deficit/hyperactivity disorder.

This study investigated EEG differences between children with two subtypes of Attention-Deficit/Hyperactivity Disorder (ADHD) and normal control subjects. 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, and the mean frequency for each band was calculated. Ratio coefficients were also calculated between frequency bands. Mean group differences were found in the theta, alpha, and beta bands between all three groups. Similarly, differences were found between all three groups for the theta/alpha and theta/beta ratios and for the mean frequency of the total EEG. These results support a model of ADHD resulting from a developmental deviation rather than a maturational lag in the central nervous system. Differences between the clinical groups in frontal activity suggest that different neuroanatomical systems are involved in the different subtypes of ADHD.

Adolescent↗

PubMed2000

Detection of feigned recognition memory impairment using the old/new effect of the event-related potential.

Twenty-four undergraduate university students with no known neurological disorders completed the Recognition Memory Test (Warrington, A., 1984. Recognition Memory Test manual. Windsor, Berkshire: NFER-Nelson.) while event-related potentials (ERPs) were recorded. Twelve subjects were instructed to feign a recognition memory deficit (malingering group), while the remainder served as controls. The malingerers performed poorly on the test compared to the control group. The 'old/new effect', an ERP measure thought to reflect recognition memory processes, did not differ between the groups, indicating recognition of previously learned material in the malingering group despite poor test performance. The study also revealed a second, early, old/new effect, maximal at left frontal sites in the malingering relative to the control group, suggesting task-related processing differences between the two groups. These effects appear to be of potential value in the detection of malingering of cognitive impairment in the clinical situation.

Adult↗

PubMed2000

EEG alpha activity and the ERP to target stimuli in an auditory oddball paradigm.

Peak-to-peak amplitudes of the N1P2 and N2P3 components in the target ERPs from a fixed interstimulus interval auditory oddball paradigm were investigated as a function of within-subject pre-stimulus levels of alpha activity. Fourteen subjects were each presented with 600 auditory stimuli in a two-tone auditory oddball paradigm which required a button-press to targets, presented with 50% probability. Pre-stimulus alpha activity at Pz was assessed for each trial by digital filtering from 8 to 13 Hz, and alpha RMS amplitude was used to sort the ERPs at Pz and Cz. A direct relationship was obtained between component amplitudes at both Pz and Cz and pre-stimulus alpha level at Pz. Component latencies were strongly related to post-stimulus alpha peaks and troughs. These data confirm the intimate relationship between central nervous system activation, as evidenced by spontaneous EEG in the pre-stimulus period, and the ERP resulting from stimulus presentation.

Acoustic Stimulation↗

PubMed2000

Removal of ocular artifact from the EEG: a review.

Eye movements cause changes to the electric fields around the eyes, and consequently over the scalp. As a result, EEG recordings are often significantly distorted, and their interpretation problematic. A number of methods have been proposed to overcome this problem, ranging from the rejection of data corresponding temporally to large eye movements, to the removal of the estimated effect of ocular activity from the EEG (EOG correction). This paper reviews a number of such methods of dealing with ocular artifact in the EEG, focusing on the relative merits of a variety of EOG correction procedures. Issues discussed include the distinction between frequency and time domain approaches, the number of EOG channels required for adequate correction, estimating correction coefficients from raw versus averaged data, differential correction of different types of eye movement, the most suitable statistical procedure for estimating correction coefficients, the use of calibration trials for the estimation of correction coefficients, and the distinction between 'coefficient estimation' and 'correction phase' error. A suggested EOG correction algorithm is also described.

Artifacts↗

PubMed2000

EOG correction: comparing different calibration methods, and determining the number of epochs required in a calibration average.

OBJECTIVE: A form of EOG correction called the 'aligned-artifact average' (AAA) method has been advanced by the authors. In contrast to many previous methods, this used a correction coefficient (B), based on an average of eye movements rather than raw data, to remove eye movement related contamination from the EEG. The first part of this study was aimed at determining whether a variation of this procedure that is more easily implemented would produce a similar correction. The second part was designed to determine the number of epochs needed in an average to correct adequately. METHODS: Subjects performed a series of eye movement tasks whilst EEG and EOG data were recorded. Data were manipulated according to either the AAA or an alternate new ERP method (NERP) and the resultant Bs were compared in part A. In part B, averages were created from varying numbers of epochs, and the resultant r(2)-values were compared. RESULTS: The AAA and NERP methods produced the same Bs, and averages with at least 40 epochs were required for adequate B estimation for both VEOG and HEOG. CONCLUSION: There is no difference between the AAA and NERP methods and thus it is acceptable to use the more easily implemented NERP method for EOG correction. It is recommended that when applying this procedure, at least 40 epochs should be used to make up the averages from which to calculate correction coefficients.

Adolescent↗

PubMed2000

EOG correction of blinks with saccade coefficients: a test and revision of the aligned-artefact average solution.

OBJECTIVE: The 'aligned-artefact average' (AAA) procedure was advanced by the authors as a technique suitable for removing eye movement-related artefacts from the EEG. It was proposed that this method would correct both blink and non-blink artefact from the EEG, using the same set of correction coefficients (Bs). However, recent evidence suggests that this simplification is not always accurate. Thus, we test here a revision of the AAA, including an appropriate allowance for the radial EOG (REOG) component, that does allow the use of the same Bs for the correction of blink and non-blink artefact. METHODS: Blink (and saccade) ERP data from 15 subjects were corrected using the AAA method, with Bs calculated from the same blink (and saccade) data set (referent waveforms), or a different set of blink (and saccade) data, or using the new revised AAA procedure (RAAA). RESULTS: AAA Bs calculated from saccades corrected blinks poorly (and vice versa). However, the RAAA Bs corrected blink ERPs better than blink-derived Bs, and saccade ERPs better than saccade-derived Bs. It was also found that irrespective of correction type, inclusion of REOG improved correction. CONCLUSION: EOG correction is more accurate when the radial channel is included, but inclusion of REOG (and/or HEOG) is not sufficient to resolve the discrepancy between blink and saccade correction. Using the RAAA procedure, both blink and non-blink data can be corrected using the same set of Bs.

Adolescent↗

PubMed2000

EOG correction: which regression should we use?

Electrooculogram (EOG) correction is used to remove eye-movement-related contamination from electroencephalograms (EEG). Correction is reliant on the regression procedure, although when multiple EOG channels are used in the correction, the appropriate type of regression to use is not known. In the present study, we aimed to resolve this matter. Computer simulations were used to compare the simultaneous, multiple-stage, and single-channel regression methods of correction. EOG propagation was modeled on prior findings, under conditions of varying vertical and horizontal EOG (VEOG/HEOG) correlation. The dependent variable was the correlation between the uncontaminated and the corrected EEG. The simultaneous regression procedure gave the best correction, with its advantage increasing as a function of VEOG/HEOG correlation. It is recommended that the simultaneous regression procedure be used for EOG correction of the EEG.

Algorithms↗

PubMed1999

Age-related changes in quantitative EEG in attention-deficit/hyperactivity disorder.

BACKGROUND: Attention-deficit/hyperactivity disorder (ADHD) in children and adolescents is characterized by excessive restlessness and an extremely poor concentration span, resulting in impulsive and disruptive behavior. Clinical observation of ADHD in adults suggests that the hyperactivity component is diminished although the impulsive type behaviors remain apparent. EEG studies of children and adolescents with ADHD have reported significantly higher levels of low frequency activity (predominantly theta) and lower levels of beta activity than normal controls. METHODS: We examined the relationship between the age-related changes reported in clinical observation and changes in EEG activity occurring in a group of ADHD patients ranging in age from 6 to 42 years. Quantitative EEGs were obtained from the midline sites of 25 children, 25 adolescents and 25 adults diagnosed with ADHD, and compared with those of age matched normal controls. RESULTS: Theta activity was elevated in the ADHD groups across all age groups compared with the normal controls. The extent of the reduction in relative beta activity in the ADHD groups compared to normal controls decreased with increasing age. CONCLUSIONS: Given that the hyperactivity component in ADHD reduces with age while the impulsivity component remains, these data, in ADHD, suggest that decreased beta activity may be linked to hyperactivity and increased theta activity to impulsivity.

Adolescent↗

PubMed1999

Eye movements reflect impaired face processing in patients with schizophrenia.

BACKGROUND: Impaired processing of faces in patients with schizophrenia may underlie aspects of disturbance in their social interaction. This study examined patterns of eye fixation in subjects with schizophrenia and non-psychiatric controls, while processing a high resolution picture of a neutral face and a nonbiological complex geometric stimulus. METHODS: Ten-second sequences of eye movement were recorded video-oculographically (50 samples/sec) while subjects were "free-viewing" the stimuli. An essential element of the study was customized software that ensured stimulus presentation on a video display only after subjects were fixated upon a centre-screen cue, so that all subjects began stimulus processing from the same point. RESULTS: Compared with the control group, subjects with schizophrenia exhibited reduced scanpath lengths and a tendency toward fewer fixations for the face stimulus. They also showed an initial relative right spatial hemineglect (for the first voluntary fixation) when viewing the Rey figure, but not when viewing the face stimulus. Overall, there were no significant differences between the schizophrenia and control groups in the lateral distribution of subsequent fixations for either stimulus. CONCLUSIONS: Disturbed spatial and temporal patterns of eye movement in some people with schizophrenia may reflect sub-optimal processing of face stimuli, that may predispose these individuals to dysfunctional interpretation of facial communication cues.

Adult↗

PubMed1999

An investigation of the event-related slow-wave potential (0.01-2 HZ) in normal children.

Previous research has indicated that the auditory ERPs of children are dominated by a frontal negative slow-wave. This paper outlines a preliminary attempt to separate event-related low-frequency activity from traditional ERP components as found in older subjects. An active auditory oddball task was completed by 30 normal children aged from 8 to 18 years, and ERPs to target and standard stimuli were derived. The original ERP files were digitally filtered to calculate separate ERPs containing only 0.01-2 Hz activity (termed the SW-ERP) or 2-12 Hz activity (termed the RESIDUAL ERP) for each subject. The SW-ERP was maximally correlated with the slow-wave factor from a principal components analysis of the original target and standard waveforms. The SW-ERPs to target stimuli contained an early negative component which showed an age-related decrease, and a late positive component which did not. The SW-ERP was found to be partly responsible for the differences in component amplitude and morphology between sites observed in the raw ERPs.

Acoustic Stimulation↗

PubMed1999

Simultaneous EEG and EDA measures in adolescent attention deficit hyperactivity disorder.

Adolescent unmedicated ADHD males and age- and sex-matched normal control subjects were examined simultaneously using EEG and EDA measures in a resting eyes-open condition. ADHD adolescents showed increased absolute and relative Theta and Alpha1 activity, reduced relative Beta activity, reduced skin conductance level (SCL) and a reduced number of non-specific skin conductance responses (NS.SCRs) compared with the control subjects. Our findings indicate the continuation of increased slow wave activity in ADHD adolescents and the presence of a state of autonomic hypoarousal in this clinical group.

Adolescent↗

PubMed1999

Evoked cardiac response components in cognitive processing: differential effects of amyotrophic lateral sclerosis.

We investigated the mechanism of two evoked cardiac response components associated with different aspects of information processing. Innocuous stimuli presented in an irrelevant condition elicit a simple cardiac deceleration termed ECR1. The same stimuli presented in a relevant condition (such as results from requesting subjects to silently count the stimuli) elicit a complex biphasic response with a large secondary acceleration in heart rate. This difference is attributed to the additional effect of cognitive task performance, resulting in an addition response component, ECR2. This may be realised by subtraction of the two responses. We investigated the mechanisms involved by comparing cardiac response profiles from a neurologically-impaired group with those from a control group amyotrophic lateral sclerosis (ALS) has been associated with a loss of synaptic connections in the frontal lobe. Twelve ALS clinically non-demented patients were age-matched with twelve neurological patients without pathological changes in the brain. Cardiac response profiles for ECR1 and ECR2 were examined as a function of group. ECR1 did not differ between the groups, but ECR2 was significantly impaired in the ALS patients. The results are discussed in terms of different brain regions associated with these two cardiac response components. ECR1 may be associated with automatic preattentive stimulus registration involving, in the case of auditory stimuli, the auditory analyser and associated pathways, while ECR2 appears to be a correlate of controlled executive processing, involving the frontal cortex.

Acoustic Stimulation↗

PubMed1999

Is the target-to-target interval a critical determinant of P3 amplitude?

The P3 amplitude is augmented by decrements in target-probability, increments in the number of nontargets preceding the target, and extensions of the interstimulus interval (ISI). Each of these changes prolongs the target-to-target interval (TTI) and, consequently, results attributed to these factors might, at least partially, be accounted for by the TTI. Recent research also indicates that the P3s elicited by targets in one-, two-, and three-stimuli tasks (in which the TTI remains invariant) are similar. However, the TTI has not been examined systematically in previous research. The present study had subjects listen to a randomized ISI (0.5, 1, 2, or 4 s) version of the auditory oddball task in which targets occurred after one, two, three, four, or five nontargets. Event-related potentials were analyzed based on ISI, sequential structure, and TTI. The study examined sequence and ISI effects independent of TTI effects and demonstrated that extensions of ISI affected N1 but not P3 amplitude, extensions of TTI enhanced P3 amplitude independent of sequential structure, and sequential structure failed to influence P3 amplitude when TTI was controlled.

Adult↗