Biomedical subjects

Jacqueline A Rushby

Publications and source records attributed to Jacqueline A Rushby.

8 recordsLinked to original sources

PubMed2006

An orienting reflex perspective on anteriorisation of the P3 of the event-related potential.

In the Go/NoGo task, the P3 component of the event-related potential elicited by NoGo stimuli is topographically anterior to that from Go stimuli. This anteriorisation has been linked to the response inhibition thought to be required when NoGo stimuli are presented, and suggested as an index of inhibition. We report a preliminary investigation of this question from an orienting reflex (OR) perspective, in which the autonomic skin conductance response (SCR) was used as an OR "yardstick". We presented subjects with a random mix of 15 target and 15 non-target auditory stimuli with a short inter-stimulus interval, and explored the sources of the resultant P3s using low-resolution electromagnetic tomography (LORETA). Across-subject mean SCRs showed exponential decrement over trials and a larger response to targets, as expected from the OR perspective. LORETA analysis of the across-subject mean initial P3s showed exponential response decrement of their common sources, suggestive of the Novelty P3. Grand mean P3s to targets and non-targets appeared to correspond to the P3b and P3a, respectively. These results suggest that anteriorisation of the P3 to NoGo stimuli may reflect processing related to the basic involuntary OR to indifferent (non-significant) stimuli rather than an active inhibitory process.

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

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

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↗

PubMed2004

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↗

PubMed2004

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↗

PubMed2004

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↗

PubMed2002

Event-related potential correlates of serial-position effects during an elaborative memory test.

Twenty undergraduate students participated in an elaborative learning test to evaluate the relationship between electrical brain activity and subsequently recalled and not-recalled words. Data collected from the midline (Fz, Cz, Pz) and lateral scalp sites (F3, F4, C3, C4, P3, P4) were analysed. The difference between event-related potentials (ERPs) elicited by subsequently recalled and not-recalled words, the ERP memory effect, was evaluated for each portion (primacy, plateau and recency) of the serial-position curve (SPC). We compared peak amplitudes for the P1, N1, P2, N400, P3 and frontal positive slow wave (FPSW) components. The electrophysiological data support the hypothesis that different mechanisms underlie primacy and recency effects during free recall paradigms. There was no support for the hypothesis that an association arises between memory and the FPSW when subjects utilise elaborative learning strategies. The P2 component predicted subsequent recall at the primacy portion of the SPC, and P1 predicted recall at the primacy and plateau portions of the curve. The findings suggest that the early positive components of the ERP (i.e. P1 and P2) are useful indices of the differential stimulus processing during elaborative learning which predicts later recall.

Adult↗