Biomedical subjects

Stuart J Johnstone

Publications and source records attributed to Stuart J Johnstone.

25 records · Page 2Linked to original sources

PubMed2003

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↗

PubMed2003

Preferred EEG brain states at stimulus onset in a fixed interstimulus interval auditory oddball task, and their effects on ERP components.

Previous work has indicated the importance of ongoing EEG activity in the elicitation of the event-related potential (ERP), supporting the conceptualisation of the ERP in terms of amplification and attenuation of component frequencies in the EEG. We investigated the importance of the phase of narrow-band EEG activity in generating N1 and P2 components in the auditory ERP. An auditory oddball paradigm requiring a button-press response to targets, with fixed interstimulus interval (ISI) and 15% target probability, was utilised. The continuous EEG at Cz was recorded from 16 subjects as the raw data set. Offline digital filtering was used to separate the EEG into 13 narrow bands from 1 to 13 Hz. For each band, the phase at the onset of each non-target stimulus was determined. These were used to sub-average the unfiltered data stream at each of four phases for each of 13 frequencies for each subject. Phase effects were examined in terms of two orthogonal dimensions of electrical brain activity: Cortical negativity and negative driving. Stimulus onset varied as a function of these dimensions in a non-random fashion across frequency, indicating the preferential occurrence of particular phases, interpretable as preferred brain states. Large differential effects were also apparent in N1 and P2 amplitudes. These data indicate important aspects of brain dynamics, suggesting that in a fixed-ISI paradigm the component frequencies of the EEG are dynamically adjusted in order to provide particular brain states at stimulus occurrence to facilitate the brain's processing of the stimulus.

Acoustic Stimulation↗

PubMed2003

A review of electrophysiology in attention-deficit/hyperactivity disorder: I. Qualitative and quantitative electroencephalography.

OBJECTIVE: This article reviews the electroencephalography (EEG) literature in relation to attention-deficit/hyperactivity disorder (AD/HD). METHODS: The review briefly outlines the history of the disorder, focusing on the changing diagnostic systems which both reflect and constrain research into AD/HD. Both qualitative and quantitative EEG studies are examined, and their results are discussed in relation to various models of AD/HD. Implications of these data for future research and development in AD/HD are considered. RESULTS: In terms of resting EEG, elevated relative theta power, and reduced relative alpha and beta, together with elevated theta/alpha and theta/beta ratios, are most reliably associated with AD/HD. Theta/alpha and theta/beta ratios also discriminate diagnostic subgroups of AD/HD. Recent studies of EEG heterogeneity in this disorder indicate the existence of different profiles of cortical anomalies which may cut across diagnostic types. CONCLUSIONS: The research to date has identified a substantial number of EEG correlates of AD/HD which hold promise for improving our understanding of the brain dysfunction(s) underlying the disorder. Further work in this field may benefit from a broader conceptual approach, integrating EEG and other measures of brain function.

Attention Deficit Disorder with Hyperactivity↗

PubMed2003

A review of electrophysiology in attention-deficit/hyperactivity disorder: II. Event-related potentials.

OBJECTIVE: This article reviews the event-related potential (ERP) literature in relation to attention-deficit/hyperactivity disorder (AD/HD). METHODS: ERP studies exploring various aspects of brain functioning in AD/HD are reviewed, ranging from early preparatory processes to a focus on the auditory and visual attention systems, and the frontal inhibition system. Implications of these data for future research and development in AD/HD are considered. RESULTS: A complex range of ERP deficits has been associated with the disorder. Differences have been reported in preparatory responses, such as the contingent negative variation. In the auditory modality, AD/HD-related differences are apparent in all components from the auditory brain-stem response to the late slow wave. The most robust of these is the reduced posterior P3 in the auditory oddball task. There are fewer studies of the visual attention system, but similar differences are reported in a range of components. Results suggesting an inhibitory processing deficit have been reported, with recent studies of the frontal inhibitory system indicating problems of inhibitory regulation. CONCLUSIONS: The research to date has identified a substantial number of ERP correlates of AD/HD. Together with the robust AD/HD differences apparent in the EEG literature, these data offer potential to improve our understanding of the specific brain dysfunction(s) which result in the disorder. Increased focus on the temporal locus of the information processing deficit(s) underlying the observed range of ERP differences is recommended. Further work in this field may benefit from a broader conceptual approach, integrating EEG and ERP measures of brain function.

Attention Deficit Disorder with Hyperactivity↗

PubMed2003

Event-related slow-wave activity in two subtypes of attention-deficit/hyperactivity disorder.

OBJECTIVE: Previous time-frequency studies have indicated that event-related low-frequency activity has important effects on component topography and developmental effects in auditory event-related potentials (ERPs) of children and adolescents. This study investigated the influence of event-related slow-wave (SW) (0.01-2 Hz) activity in the group differences seen between children with and without attention-deficit/hyperactivity disorder (AD/HD) of different subtypes. METHODS: Time-frequency analysis techniques were applied to auditory ERP data derived from children with AD/HD predominantly inattentive type (n = 30), AD/HD combined type (n = 30) and age-matched control subjects (n = 30). RESULTS: Event-related early frontal negative and late posterior positive SW components were reduced in the AD/HD combined type group, but not AD/HD inattentive type group, relative to controls. The RESIDUAL ERPs, which represented event-related 2-12 Hz activity, showed clinical vs. control group differences in components that were similar in both AD/HD subtype groups. CONCLUSIONS: The time-frequency results showed that event-related SW (0.1-2 Hz) activity contributes importantly to group differences between AD/HD and control children, and the pattern of group differences from controls for each of the AD/HD subtype groups, which are evident in raw ERPs. These results emphasise both the clinical and developmental importance of this form of analysis. SIGNIFICANCE: This novel approach revealed additional specific information about stimulus processing and regional inhibition/activation in two AD/HD subtypes, relative to control subjects.

Adolescent↗

PubMed2003

Aiding diagnosis of attention-deficit/hyperactivity disorder and its subtypes: discriminant function analysis of event-related potential data.

BACKGROUND: Robust evidence exists that the brain functioning of children and adolescents with attention-deficit/hyperactivity disorder (AD/HD) differs from that of normal controls. The purpose of this study was to further investigate whether event-related potential (ERP) measures of brain function could be used to reliably classify normal controls versus children and adolescents with two subtypes of AD/HD. METHODS: Behavioural and topographic ERP data from children aged 8-12 years (n = 75) and adolescents aged 13-18 years (n = 75) were entered into stepwise discriminant function analyses separating controls and subjects with AD/HD, and also subjects with AD/HD-Predominantly Inattentive type (AD/HDin) from those with AD/HD-Combined type (AD/HDcom). RESULTS: For children aged 8-12 years, controls and children with AD/HD could be separated with an overall classification accuracy of 73.3%, and the AD/HD subtypes were classified with 69.4% overall accuracy. For adolescents aged 13-18 years, 58.7% of the control vs. AD/HD subjects were correctly classified, and 62.7% of subjects in the subtypes. Classification function coefficients for each of these discriminations are presented for the purposes of cross-validation. CONCLUSIONS: In children aged 8-12 years, analysis of ERP data may aid a clinician in diagnosing AD/HD, although the clinical utility of ERP analysis is reduced for adolescents aged 13-18 years. Suggestions are made to combine ERP measures with other measures of brain function in order to improve classification accuracy, and also to predict drug response in children diagnosed with AD/HD.

Adolescent↗

PubMed2002

Event-related potentials reveal processing differences in honest vs malingered memory performance.

Twenty-two undergraduate students completed a recognition memory test while event-related potentials (ERPs) were recorded. During the testing phase, subjects distinguished old from new words in a forced-choice format. There were two counterbalanced within-subject conditions, one in which subjects performed to the best of their abilities, and another with instructions to feign memory impairment. Test scores and response latencies differed significantly between the two conditions. Analysis of PCA-defined epochs revealed that old words were more positive than new in the control condition, with this difference confined to frontal regions and interpreted as reflecting familiarity-based recognition judgements. In the malingering task, this old/new word difference emerged earlier and was broadly distributed across the scalp. A discriminant function analysis using reaction time and ERP measures resulted in 82% correct classification of honest and simulated performance, with 79% correct on cross-validation.

Adolescent↗