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Biomedical subjects

R J Barry

Publications and source records attributed to R J Barry.

At least 37 records · Page 2Linked to original sources
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↗
PubMed1998

EEG analysis in Attention-Deficit/Hyperactivity Disorder: a comparative study of two subtypes.

This study investigated differences in the EEG between children with Attention-Deficit/Hyperactivity Disorder of the Combined Type, Attention-Deficit/Hyperactivity Disorder of the Predominantly Inattentive Type and control subjects. All subjects were between the ages of 8 and 12 years, and groups were matched on age and gender. The EEG was recorded during an eyes-closed resting condition from 21 monopolar derivations and these were clustered into nine regions prior to analysis. One minute of trace was analysed using Fourier transformation to obtain both absolute and relative power estimates in the delta, theta, alpha and beta frequency bands. The patient groups were found to have greater levels of theta and deficiencies of alpha and beta in comparison to the control group. Children with Attention-Deficit/Hyperactivity Disorder of the Predominantly Inattentive type were found to be significantly different from those of the Combined type in the same measures, appearing to be closer to the normal profiles. The general results support a maturational lag model of the central nervous system in Attention Deficit/Hyperactivity Disorder. The differences between the subtypes suggest a difference in the severity of the disorder rather than a different neurological dysfunction.

Attention Deficit Disorder with Hyperactivity↗
PubMed1998

EOG correction: a new perspective.

OBJECTIVE: In the field of EOG correction, discrepancies have been found between the propagation rates for different types and frequencies of eye movement. This study attempted to determine whether these differences could be explained by the affect of EOG magnitude on the correction procedure. METHODS: Experiment 1 utilized simulated data to determine whether the combination of EOG magnitude and other forms of interference distorted the estimation of the propagation coefficients (Bs). Experiment 2 used real data to determine if the patterns obtained in Expt. 1 were apparent in real data. RESULTS: Matched t tests found that simulated low power EOG produced inflated Bs as a function of interference in Expt. 1. Experiment 2 found the same relationship between B and EOG magnitude as with the simulations. CONCLUSIONS: The findings are consistent with the thesis that eye movement related fields propagate similarly for a range of EOG types and frequencies, suggesting that the B differences reported in the literature are artifactual, and indicating the need for a new correction procedure.

Adult↗
PubMed1998

EOG correction: a new aligned-artifact average solution.

OBJECTIVE: In the field of EOG correction, discrepancies have been found between the propagation rates for different types and frequencies of eye movement. However, Croft and Barry demonstrated that these differences can be explained by the affect of EOG magnitude on the correction procedure (Croft, R.J. and Barry, R.J. EOG correction: a new perspective. Electroenceph. clin. Neurophysiol., 1998, 107: 387-394). This study utilized a new 'aligned-artifact average' technique (AAA) to examine whether propagation is constant across eye movement types and frequencies, and tested the AAA as an EOG correction tool. METHODS: Two experiments manipulated interference levels in real data sets to determine if interference affected propagation coefficients (Bs). The third tested real data for the effect of forward propagation of eye movement related neural potentials on Bs, and the fourth utilized computer simulations to assess the effectiveness of the new AAA correction procedure. RESULTS: Interference was found to inflate B at low EOG amplitude, and its removal removed B variation and inflation. The forward propagation of eye movement related neural potentials had very little effect on B. The AAA procedure produced near perfect corrections of the simulated data, superior to a comparison method. CONCLUSIONS: EOG propagation is constant across eye movement types and frequencies, and thus only one correction coefficient should be calculated and applied to data. The AAA method provides a more accurate correction and makes possible, for the first time, the adequate correction of posterior sites.

Artifacts↗
PubMed1998

Decrement of the N1 auditory event-related potential with stimulus repetition: habituation vs. refractoriness.

We examined whether the amplitude decrement traditionally found for the N1 peak of the event-related potential (ERP) with repetition of auditory stimuli results from the process of habituation or from the refractory period of the neural elements underlying the N1 response. These competing accounts of the process underlying the N1 decrement with repetition differ in terms of the predicted effects of variations in stimulus repetition and interstimulus interval (ISI). These predictions were examined using a short-term habituation design with a factorial combination of stimulus repetition and ISI. Forty-five subjects received 21 stimulus trains, each consisting of seven innocuous tones, all at 1 kHz except the sixth, which was a 1.5-kHz tone. Each subject was assigned to one of three ISI conditions (either 1, 3 or 10 s). The results provide little support for the view that N1 response decrement with stimulus repetition reflects a process of habituation. The present results provide greater support for the view that this decrement is based on the separate refractory periods or recovery cycle processes of at least two neural generators contributing to activity in the N1 peak latency range.

Acoustic Stimulation↗
PubMed1998

Older? Who me? Growing old should not mean giving up.

The strangest things precipitate the most interesting discussions. It is interesting how frequently the word "older" appears in our language. It has been there all along, we have just become sensitized to its presence. The same may be true for you as you read the commentary on the next two pages and begin to reflect on the stereotypes and limitations placed on "older" people. Are they justified in the present day, or are they simply carryovers from the past, or is there some element of harsh reality to the characterizations?

Aged↗
PubMed1997

Decomposing skin conductance into tonic and phasic components.

Overlapping phasic skin conductance responses (SCRs) obtained using short interstimulus interval (ISI) paradigms such as those employed in cognitive research, confound measurement of each discrete phasic SCR as well as the tonic skin conductance level (SCL). We report a method of resolving this problem using a modelling technique that takes advantage of the stereotyped nature of the within-subject SCR waveform. A four-parameter sigmoid-exponential SCR model that describes the entire response, was developed and extended to five-, six- and eight-parameter skin conductance (SC) models. These SC models were successfully curve-fitted to more than 60 SC segments, each containing one SCR or two overlapping SCRs on a sloping baseline obtained from 20 normal subjects. The SC segments were consequently decomposed into their components: the tail of the previous response, one or two SCRs and the SCL. The SCRs free of the complication of overlap were then quantified. The raw SCRs of the same data set were also measured using a standard method. The standard measurement showed a significant reduction of 15% in amplitude and 140 ms in peak latency compared to our method. The basic four SCR model parameters--onset time, rise time, decay time constant and gain--showed increasing inter-subject variability in that order. These SCR model parameters may be studied as variables in normal and patient groups and as indices of treatment response. This quantitative method also provides a means to assess the relationships between central and autonomic psychophysiologic measures.

Adult↗
PubMed1997

Influence of diazepam and buspirone on human heart rate and the evoked cardiac response under varying cognitive load.

The influence of two anxiolytics on basal heart rate and on the evoked cardiac response elicited by auditory stimuli, was studied in humans. Diazepam (Valium) (7.5 mg) and buspirone (Buspar) (7.5 mg), which differ in their psycho-pharmacological profiles, were used. Prestimulus vigilance and cognitive load were manipulated by instructions allowing the subjects to ignore the stimuli, or requiring them to count the tones. Drug effects were obtained in subjective alertness, basal heart rate level, and the evoked cardiac response. Diazepam reduced subjective alertness, while buspirone did not. Diazepam apparently increased heart rate levels relative to placebo, in contrast to buspirone, which produced an apparent decrease in heart rate. These drug-induced prestimulus heart rate level effects were associated with differential decelerations immediately following stimulus onset and appear to reflect differences in prestimulus vigilance. Opposite effects of the drugs were also observed in the second, acceleratory, component of the of the evoked cardiac response, and these were found to be independent of the prestimulus drug effects. Compared with placebo, buspirone appeared to enhance the acceleratory component in the count condition, while diazepam led to an apparent reduction of this component. Enhancement of this acceleration after buspirone may reflect an increase in cognitive effort directed to the performance of task-relevant behaviour, while the reduction of this component after diazepam can be regarded as a cognitive-motivational neutralisation of signal value. The differential effects of the two anxiolytics support the separation of the evoked cardiac response into different components and may also have implications for the clinical use of the drugs.

Acoustic Stimulation↗
PubMed1996

Auditory event-related potentials to a two-tone discrimination paradigm in attention deficit hyperactivity disorder.

Auditory event-related potentials (ERPs) were recorded from 10 children diagnosed with attention deficit hyperactivity disorder (ADHD) and 10 age-, sex-, and IQ-matched control children. ERPs were recorded from 17 electrodes during an auditory two-tone discrimination ("oddball') paradigm. Subjects were instructed to press a hand-held response button to infrequently presented target tones. ERP components elicited to target and non-target stimuli were analyzed for between-group differences. Results indicated that for the children with ADHD relative to control children, an N2 component to non-target stimuli was larger in the posterior region and smaller in the frontal region. The P3b component to target stimuli was smaller in the posterior region and larger in the frontal region for the ADHD group compared with the control group. The between-group differences in P3b scalp distribution are indicative of a between-group difference in the neural generators of P3b. It is proposed that the ADHD group, relative to controls, utilizes an additional cognitive process when processing task-relevant stimuli. This process is more frontally distributed and may reflect an attentional compensation mechanism in the ADHD group.

Adolescent↗
PubMed1996

Age-related changes in child and adolescent event-related potential component morphology, amplitude and latency to standard and target stimuli in an auditory oddball task.

Previous studies of auditory event-related potentials (ERPs) to an oddball task in children and adolescents focus on responses to target stimuli and provide little detail of age-related changes to standard stimuli. In this study, age-related changes in behavioural responding and ERP component morphology, amplitude and latency to standard and target stimuli were examined. Auditory ERPs to an oddball task were recorded from the midline sites (Fz, Cz and Pz) of 50 subjects aged 8 to 17 years 11 months. Behavioural results indicate a decrease in reaction time and errors of commission with age. To standard tones, N2 amplitude and N1 latency showed a linear decrease with age while an increase with age was found for P2 amplitude. For target tones, N1 and N2 amplitude and N1, N2 and P3 latency showed a linear decrease with age and P2 and P3 amplitude showed a linear increase with age. Age-related changes in the morphology of the ERP elicited by standard tones (especially the N2 and P2 components), as well as concurrent morphological changes in standard and target tones, are discussed.

Acoustic Stimulation↗
PubMed1996

Preliminary process theory: towards an integrated account of the psychophysiology of cognitive processes.

A brief overview of the history of the orienting reflex (OR) in western psychology is presented, in order to provide a context for a discussion of its role in attentional processing. Some aspects of observed response fractionation are discussed, leading to an outline of a coherent theory of preliminary processes in OR elicitation. This discriminates between involuntary and voluntary aspects of cognitive processing but depends on a common core mechanism. The role of state variables in modulating phasic responses is also discussed. Although this theory was developed largely from a study of autonomic responses, it has been possible to extend it to include various central measures, and recent extensions are described. A number of recent studies are briefly outlined to provide examples demonstrating the use of a range of physiological measures (central and peripheral) in a variety of situations (from pistol range to the laboratory) with different subject groups (adults, children and psychiatric patients). Finally, the use of heart rate data in the investigation of task-relevant cognitive load is discussed as a relatively simple but sensitive index to explore drug and other effects in cognition. These examples indicate the wide-ranging potential benefits of using psychophysiological approaches in the study of cognitive processes.

Attention↗
PubMed1995

Numbers of preceding nontargets differentially affect responses to targets in normal volunteers and patients with schizophrenia: a study of event-related potentials.

This event-related potential study systematically varied the number of nontargets (1, 3, 5, 7, 9) preceding the target tone in an oddball experiment and examined the effect of this on N2, P3, and reaction time measures in schizophrenic patients and normal volunteers. Schizophrenic patients were found to have reduced P3 amplitudes, but this reduction was restricted to series when the targets followed an intermediate number (3-7) of nontargets, and not when targets followed a short (1) or long series (9) of nontargets. Although other interpretations of this finding are possible, the pattern of results could be explained by the hypothesis that the refractory period governing the generation of the P3 component was prolonged in schizophrenia.

Adult↗