Journal of Clinical EEG & Neuroscience, April, 2006

ABSTRACTS:
The 15th Annual Conference of the Australian Society for Psychophysiology

December 9-11, 2005
University of Wollongong, Wollongong, Australia

Page 1 2 3

EEG abnormalities in adolescent males with AD/HD

Megan J. Hobbs,1 Adam R. Clarke,1 Robert J. Barry,1 Rory McCarthy2 and Mark Selikowitz2

1Brain & Behaviour Research Institute and Department of Psychology,
University of Wollongong, Wollongong, Australia
2Sydney Developmental Clinic, Sydney, Australia

Introduction: This study investigated EEG abnormalities in adolescents with Attention-Deficit/Hyperactivity Disorder (AD/HD).

Methods: Fifteen AD/HD and 15 control subjects participated in this study. All subjects were between 14 and 17 years of age. The EEG was recorded from 19 electrode sites and was analysed to provide estimates of both absolute and relative power in the delta, theta, alpha and beta bands. Theta/alpha and theta/beta ratio coefficients were also calculated.

Results: Across the scalp AD/HD subjects were characterised by greater absolute delta and theta activity, and an increased theta/beta ratio compared to controls. No group differences were found for either absolute or relative alpha, or absolute beta. AD/HD subjects demonstrated a reduction in relative beta activity in the posterior region.

Discussion: The AD/HD group showed significant deviations from normal CNS development, in particular in posterior regions. These results support previous claims that this type of EEG abnormality is most likely to be found in older individuals with AD/HD. This is the first study to investigate EEG abnormalities in adolescents with AD/HD during an eyes-closed resting condition. Results are also representative of a late-diagnosed AD/HD adolescent group that has not been previously discussed within the literature.

Email: mjh64@uow.edu.au

Examining the sensitivity of an integrated approach in predicting severity of non-clinical depression: Preliminary findings

Patrick Hopkinson,1,2,3 Blossom C.M. Stephan,3 Evian Gordon,1,2,3 Leanne M. Williams1,2 and Andrew H. Kemp1

1The Brain Dynamics Centre and 2Discipline of Psychological Medicine, University of Sydney, Sydney, Australia
3The Brain Resource Company, Sydney, Australia

Introduction: Depressed mood is characterised by disturbances in cognition, personality and psychophysiology; in particular, autonomic function and event-related potentials. However, theoretical models tend to focus on a single domain of dysfunction. In this study, we determined the value of combining cognitive, personality and psychophysiological measures in predicting level of depression, towards a goal of developing an integrative neuroscience model of depression.

Methods: 266 participants were classified as either non-depressed, mild-moderately or severely depressed on the basis of the DASS-21 depression subscale scores. Analysis of variance identified variables on which the categorised participants differed. Significant variables were then entered into a series of stepwise regressions to examine their ability to predict depression scores.

Results: An integrated model including cognitive, personality and psychophysiological measures was found to predict substantially more of the variation in depression severity than single domains of function.

Discussion: These findings suggest that it is important to consider an integrated approach when trying to understand the mechanism of depression. Each domain may contribute unique explanatory information consistent with an integrative model of depression which takes into account the role of both behaviour and underlying neural changes. Given that depression is dimensional, these findings may also apply to clinical depression.

Email: patrick.hopkinson@brainresource.com

Arterial stiffness during mental challenge in normotensive young males

K. Huang, Yati N. Boutcher, M. Matuszek and Steve H. Boutcher
School of Medical Sciences, University of New South Wales, Sydney, Australia

Introduction: Arterial stiffness is a significant risk factor for cardiovascular disease. Whether arterial stiffness is increased during exposure to mental challenge, however, is undetermined. Thus, the purpose of this study is to examine the arterial stiffness response to mental challenge.

Methods: Thirty six normotensive males (21 ± 0.4 yr) performed a 10-min Stroop task after resting for 40 minutes. Applanation tonometry was used to assess Augmentation Index (AIx), a measure of arterial stiffness. Forearm blood flow was assessed by occlusion plethysmography, blood pressure through a Finapres, and cardiac output by impedance cardiography.

Results: AIx increased by 6%, from baseline -1.9 ± 1.6% to 4.0 ± 1.7% following 10 min of Stroop task (P<0.05). Heart rate increased by 12% from baseline, 68.4 ± 1.4 b(min-1 to 76.6 ± 1.2 b(min-1 following 10 min of Stroop. The increase of heart rate to Stroop was also accompanied by an increase in mean arterial pressure and forearm blood flow. AIx, however, was independent of heart rate, blood pressure, and vascular resistance response to Stroop.

Discussion: Mental challenge significantly increases arterial stiffness in young males. The influence of mental challenge induced increase in arterial stiffness on cardiovascular disease, however, is undetermined.

Email: y.boutcher@unsw.edu.au

A bilateral visual discrimination task investigating N200 response differences to exogenous and endogenous cueing: An ERP study

Raymond Inkpen, Karen Drysdale and Patricia T. Michie
School of Behavioural Sciences, University of Newcastle, Callaghan, Australia

Introduction: ERPs were utilised to investigate differences between exogenous and endogenous spatial cueing where attended and unattended letters were presented simultaneously to the left and right visual field (VF).

Method: Participants responded to target letters presented in the attended (cued) VF while ignoring stimuli in the unattended VF. There were two target letters “A” and “E” requiring a left or right hand response respectively when presented in the attended VF. Processing of stimuli in the unattended field was assessed by examining their effect on ERPs, RT and % correct when they were compatible (eg “A” in both VF), incompatible (“A” in attended, “E” in unattended VF) or neutral (“A” in the attended, “P” in unattended) with respect to attended letters.

Results: ERPs in the unattended hemisphere (contralateral to the unattended visual field) showed an increased negativity in the N200 range in the compatible and incompatible conditions relative to the neutral condition, replicating previous findings (Drysdale et al, 1995). This same pattern was evident in the endogenous condition. However there was evidence of earlier onset of N200 for exogenous cues.

Discussion: N200 in the unattended hemisphere may reflect an inhibition process of unattended target material.

Email: Raymond.Inkpen@newcastle.edu.au

Sound-induced illusory flashes: Issues for a psychophysiological investigation

Hamish Innes-Brown
Brain Sciences Institute, Swinburne University of Technology, Hawthorn, Australia.

Introduction: The first clear case where auditory information radically affects unambiguous visual perception was documented some years ago (Shams, Kamitani, Shimojo, 2000). Varying the number of auditory beeps presented coincidently with visual flashes was found to vary the number of perceived visual flashes. The illusory effect is phenomenological rather than qualitative, is stable with respect to many experimental variables and as such is thought to reflect an extensive property of polysensory mechanisms in the brain.

Methods: Classic time-locked averages (ERPs), event-related spectral perturbation (ERSP) and gamma-band responses will be compared for this data set.

Results: Although the behavioural data indicated that the illusion occurred on 53% of one-flash/two-beep trials, no differences were found in the ERPs between illusion and non-illusion trials. Examination of ERSP waveforms revealed that illusion trials showed a transient increase in gamma-band activity (40-45 Hz) at around 170 ms, while non-illusion trials showed a decrease in gamma-band power at the same time, and a transient increase in beta (20-30 Hz) power at around 100 ms.

Discussion: Although no ERP differences were found between the illusion and non-illusion trials, non time-locked dynamic changes in brain activity were found to exhibit different patterns between illusion and non-illusion trials.

Email: hinnesbrown@gmail.com

Central auditory processing deficits in patients with auditory hallucinations as revealed by event-related potentials: Preliminary results

Hamish Innes-Brown,1 Alex Sergejew,1 Tracey Shea,1 Gary Egan,2 Melissa Wright,1
Katherine Henshall,3 David Copolov1 and Susan Rossell1

1Mental Health Research Institute of Victoria, Parkville, Australia
2Howard Florey Institute and 3Department of Otolaryngology, University of Melbourne, Melbourne, Australia

Introduction: It has been proposed that auditory hallucinations (Ahs) experienced by patients with psychosis result from cortical or cortico-subcortical disconnection. The results presented here are an initial exploration of data collected examining central auditory function and cortical connectivity.

Methods: 22 controls, 26 non-hallucinating patients with psychosis, and 22 currently hallucinating patients with psychosis were recruited. ERPs to words and tones (presented on the left, right and bilaterally) were recorded during a passive listening task.

Results: N1 amplitudes were compared. Controls showed generally larger N1 amplitude to words and tones contralaterally. Patients showed no such effect for words. However, larger N1 was measured for right-ear tones in the left hemisphere in the non-hallucinators but not the hallucinators.

Discussion: The data from tone stimuli confirm previous studies that have shown a reduced right ear advantage behaviourally in schizophrenia patients, especially in those that hallucinate - suggesting a neurobiological origin for such behaviour. The word data suggest that more complex stimuli have a unique linguistic quality which has been more strongly lateralised. Having successfully shown basic ERP differences in the processing of lateralised words and tones in patients with psychosis, our next step is to look specifically at left-right hemisphere connectivity.

Email: hinnesbrown@gmail.com

The effects of sleep deprivation on visual evoked potentials and peripheral vision in professional drivers - preliminary results

Melinda L. Jackson,1 Rodney J. Croft,1 M.E. Howard,2 R.J. Pierce,2 K. Papafotiou1 and G. Kennedy3

1Brain Sciences Institute, Swinburne University, Melbourne, Australia
2Institute for Breathing and Sleep, Austin Health, Melbourne Australia
3Department of Psychology, Victoria University, Melbourne Australia

Introduction: Visual attention is an important aspect of driving. Sleep deprivation (SD) may cause “tunnel vision”, or an attenuation of drivers’ useful visual field. The study aimed to assess the effects of acute SD on peripheral vision in professional drivers.

Methods: Twelve truck drivers (mean age: 45.7) attended two experimental sessions; a 27-hours SD session; and a rested session following a normal night’s sleep. Drivers performed a tunnel vision task, which measured central versus peripheral visual detection and discrimination, while visual evoked potentials and reaction times were recorded.

Results: Drivers were slower to respond to peripheral targets in the SD session compared to the rested session (F(1,11) = 14.53, p<.001). P100 amplitude to peripheral stimuli was also reduced for peripheral compared to centrally-presented stimuli (F(1,11) = 6.88, p<.05), but this was not affected by SD.

Discussion: While stimuli presented to the peripheral field were processed more poorly than those centrally in terms of both behavioural and P100 changes, SD only affected the behavioural changes. Failure to respond appropriately to hazards in the periphery whilst driving may thus explain some of the increased sleep-related accident risk, however these do not appear to relate to changes to early visual processing.

Email: mjackson@swin.edu.au

Electrophysiological Correlates of Inhibition of a Task Set

Sharna Jamadar, Frini Karayanidis, Rebecca Nicholson and Patricia T. Michie
Department of Behavioural Sciences, University of Newcastle and NISAD, Callaghan, Australia

Introduction: This study explored inhibition of a task set by manipulating three conditions within subjects: a classic cued task-switch condition, a non-informative cue condition, and a no-go type condition, where an informative cue was followed by a dummy stimulus, where no response was required.

Methods: Sixteen participants alternated between a letter and a number task.

Results: Substantial sequence effects associated with the characteristics of the preceding trial were evident in reaction time (RT). Generally, RT increased for both switch and repeat trials when preceded by a no-go trial, irrespective of the condition of the current trial. An overall switch cost was evident, and again, was affected not only by the current condition, but also the condition of the preceding trial. All conditions showed a switch related positivity, but it was only significant when a classically cued trial was preceded by a classically cued trial.

Discussion: It appears that when preceded by a no-go trial, inhibition of the previously active task-set must be overcome in order to perform the current task. In general, there was a larger effect of preceding trial than current trial condition on reaction time and switch cost.

Email: Frini.Karayanidis@newcastle.edu.au

Development of inhibitory processing in the stop-signal task: Traditional and narrow-band ERP perspectives

Stuart J. Johnstone, Aneta Dimoska, Dale Chiswick, Robert J. Barry and Adam R. Clarke
Brain & Behaviour Research Institute and Department of Psychology, University of Wollongong, Wollongong, Australia

Introduction: The present study examined the development of response inhibition in the stop-signal task across child, young-adult and older-adult groups, using performance and electrophysiological indices.

Methods: Fifty-one subjects (17/age-group) performed a typical stop-signal task with a primary visual binary-choice and auditory stop-signals while EEG was recorded from 17 sites. ERPs were derived to stop-signals for successful and failed stop trials in three frequency bands: “original” (.01-30 Hz), “residual” (2-30 Hz) and “slow-wave” (.01-2 Hz).

Results: Stop-signal reaction time decreased with increasing age and then showed a small increase in the older-adult group, although inhibition probability did not differ with age. Traditional successful stop trials ERPs showed decreasing N1 and N2 and increasing P2 and P3 amplitudes with increasing age. An early negative slow-wave component decreased with age, while a late positive slow-wave component increased There were no developmental effects in the residual waveforms. In the failed stop ERPs, Pe increased with age in the original and slow-wave ERP waveforms.

Discussion: This study provides the first developmental investigation of ERPs in the stop-signal task and shows that the dissociation of slow-wave activity from the ERP waveform is crucial for the interpretation of age effects.

Email: sjohnsto@uow.edu.au

Atypical working memory updating in Attention Deficit/Hyperactivity Disorder combined and predominantly inattentive subtypes

Hannnah A.D. Keage,1 C. Richard Clark,1 Daniel F. Hermens,2 S. Clarke,2,3,4
M.R. Kohn,2,3,4 Leanne M. Williams,2 David Crewther,5 C. Lamb6 and Evian Gordon2,7

1School of Psychology, Flinders University, Adelaide, Australia
2The Brain Dynamics Centre, Westmead Hospital and
3Dept of Adolescent Medicine, Westmead Hospital, Westmead, Australia
4Meridian Clinic, Sydney, Australia
5Brain Sciences Institute, Swinburne University, Hawthorn, Australia
6Paediatrican, Adelaide, Australia
7The Brain Resource Company, Sydney, Australia

Introduction: The study investigated whether children and adolescents diagnosed with Attention Deficit/Hyperactivity Disorder Predominantly-Inattentive (AD/HD-in) and Combined (AD/HD-com) subtypes effectively register features within their environment.

Methods: Children and adolescents diagnosed with AD/HD-in (Child n=20; Adolescent n=32) or AD/HD-com (Child n=24; Adolescent n=42), and age- and sex-matched controls were presented with a series of letters on a computer-screen and were asked to respond to consecutive repeats (targets). This study specifically examined the P3 component to non-targets known to reflect the updating of working memory of task-relevant information.

Results: Compared to controls, all AD/HD groups displayed reduced frontal P3 latencies, with minor topographic variation according to subtype and age-group. The adolescent Combined group also showed reduced amplitude over posterior regions compared to controls and over left frontal regions compared to the Inattentive group. All AD/HD groups performed worse than controls in terms of commission errors and/or reaction time.

Discussion: These results suggest some general abnormality in AD/HD in frontal processes associated with the assimilation of newly relevant information, as represented in this study by target updating requirements. At the same time, observed variation in the related scalp topography suggests some minor systemic differentiation according to age or sub-type.

Email: Hannah.Keage@flinders.edu.au

Auditory ERP correlates of the evoked cardiac response to simple stimuli: Stimulus intensity and processing load effects

Carlie A. Lawrence and Robert J. Barry
Brain & Behaviour Research Institute and Department of Psychology, University of Wollongong, Wollongong, Australia

Introduction: Previous research has suggested that the complex phasic cardiac response (ECR) evoked by innocuous stimuli requiring cognitive processing may be described as the sum of two independent response components. An initial heart rate deceleration (ECR1) and a slightly later HR acceleration (ECR2), have been hypothesised to reflect stimulus registration and cognitive processing load respectively. Earlier invesitgations examined the effects of stimulus intensity and processing load on the ECR and the event-related potential, manipulating load and intensity within blocks. The current research examines manipulations of cognitive load between blocks with stimulus intensity differences within blocks.

Methods: 24 subjects were presented with randomly-interspersed soft (50 dB) and loud (80 dB) 1000 Hz tones in a variable long ISI (7-9 s) ‘oddball’ paradigm, and required to silently count, or allowed to ignore, both tones in one of two counterbalanced stimulus blocks.

Results: The ECR showed evidence of the two components, which were enhanced by counting, and showed little intensity effect. The auditory ERP showed the expected obligatory processing effects in the N1, and substantial effects of cognitive load in the late positive complex (LPC).

Discussion: These data are discussed in relation to a sequential-processing model of the orienting reflex (OR).

Email: carlie@uow.edu.au

Evidence for an early direct visual input to V5/MT

Robin Laycock,1 David Crewther,2 Paul Fitzgerald3 and Sheila Crewther1

1Department of Psychological Sciences, La Trobe University, Bundoora, Australia
2Brain Sciences Institute, Swinburne University, Hawthorn, Australia
3Alfred Psychiatry Research Centre and Department of Psychological Medicine, Monash University, Melbourne, Australia

Introduction: It has been proposed that human visual processing consists of feed-forward projections through V1 into dorsal extrastriate cortex (V5/MT). Evidence also exists, however, for an early, direct input to V5/MT which bypasses V1, and may travel via superior colliculus or the Lateral Geniculate Nucleus or both. Thus we set out to investigate the critical timing of cortical processing of motion using Transcranial Magnetic Stimulation (TMS) to disrupt V5/MT function.

Methods: Magnetic stimulation was administered to the left V5/MT region of 10 participants whilst they performed a motion direction detection task at 80% correct in a three alternate forced choice paradigm. Eighty dots moved coherently to the left, right or were stationary for between 53 ms and 84 ms. Pulses were delivered with a stimulus-TMS onset asynchrony of between 0 ms and 220 ms in 32 ms intervals after onset of the visual stimulus.

Results: Mean performance showed diminished accuracy with TMS within 32 ms post stimulus onset. Performance was unaffected at other time delays.

Discussion: This study demonstrates that accurate perception of dots moving at a speed of 2.2cm/sec requires activation of V5/MT within 32 ms of stimulus onset suggesting that such motion processing bypasses striate cortex.

Email: r.laycock@latrobe.edu.au

A TMS study of V1: Is motion processed by different pathways in different people?

Robin Laycock,1 David Crewther,2 Paul B. Fitzgerald3 and Shelia Crewther1

Introduction: Processing of visual information appears to either project from LGN to V1 and up to regions such as V5/MT, or via direct inputs from LGN to V5/MT. This study used TMS to investigate the temporal properties of V1 in motion processing.

Methods: TMS was applied to V1 whilst 10 participants completed a motion direction detection task at 80% correct in a three alternate forced choice paradigm. During the task eighty dots moved coherently to the left, right or were stationary for between 53 ms and 84 ms. The stimulus -TMS onset asynchrony varied between 0 ms and 220 ms.

Results: Mean performance showed diminished accuracy with TMS to V1. Four participants showed a strong early inhibition effect at 0 ms. Six participants showed only a non significant later inhibition effect at between 95 ms and 157 ms.

Discussion: Although definitive conclusions are premature, V1 appears to be involved with motion processing, possibly ‘gating’ feedforward projections to V5/MT. A later time period of disruption may be indicative of feedback projections into V1. Some participants however did not show this. A larger sample is required to determine whether some participants rely on different cortical strategies to process motion direction, implying different temporal activation of primary visual cortex.

Email: r.laycock@latrobe.edu.au

The effects of digital filtering on duration MMN

Sumie Leung, Rodney J.Croft and Pradeep Nathan
Brain Sciences Institute, Swinburne University of Technology, Hawthorn, Australia

Introduction: Mismatch negativity (MMN) is an event-related potential component that provides a neurophysiological representation of the acoustic change detection system. Different research groups have applied different filter settings when analysing MMN, however the most appropriate filter settings have not been established. The aim of this study was to determine which bandpass filter, of the raw EEG data, produces the optimal MMN peak amplitude.

Methods: A duration deviant MMN paradigm was recorded from 25 participants. MMN was calculated following a number of different bandpass filters. The adequacy of each filter was defined as the ratio of the resultant MMN peak relative to the standard deviation of the baseline period.

Results: Overall, MMN was clearest in the 2-4 Hz band, dropping exponentially up to 30 Hz. This differed across individuals, with preferential bands ranging from 0.1-2 Hz up to 6-8 Hz. The 2-4 Hz band was significantly better than the 0.1-30 Hz band, and the 0.1-8 Hz band (which included each individual’s preferred band) did not differ from the 2-4 Hz band.

Discussion: Since the 0.1-8 Hz band included individual’s preferential frequencies and produced similar MMN peaks to the optimal band, it is recommended that this bandpass be employed in MMN analysis.

Email: smleung@groupwise.swin.edu.au

Waking quantitative EEG in depression

Tamara D. Lorensen, Adam R. Clarke and Robert J. Barry
Brain & Behaviour Research Institute and Department of Psychology, University of Wollongong, Wollongong, Australia

Introduction: Despite almost a century of scientific enquiry into depression, it remains a baffling disorder. One of the main contributing factors to this, and one that impedes research progress, is the heterogeneity of depression. Combined with this is a wide range of research methodologies which yield inconsistent findings. This study attempts to address some of these issues by reducing confounds such as diagnostic criteria and using a systematic approach to measurement.

Method: Twenty-two normal controls and nine medication free depressed persons were assessed using the Beck Depression Inventory; the Symptom Checklist-90-R; and the DASS followed by a QEEG.

Results: Eyes closed data were used for analysis. Absolute power differences for delta, theta and beta were not significant. However, midline alpha power was significantly enhanced in the depressed subjects compared to controls, and the difference in mean alpha power across the scalp approached significance.

Discussion: As predicted, those diagnosed with depression showed EEG differences from normal controls. An important feature of this study was that all subjects were medication free at the time of testing. The results, which are suggestive of arousal deficits in depressed persons, warrant further investigation.

Email: tamara@tpg.com.au

Activation and arousal processes in normal children: An analysis of EEG topography and electrodermal activity

Christopher A. Magee, Adam R. Clarke and Robert J. Barry
Brain & Behaviour Research Institute and Department of Psychology, University of Wollongong, Wollongong, Australia

Introduction: Barry et al. (2004) distinguished between arousal (current tonic energetic level) and activation (task-related change in arousal), and proposed that these may have differing effects in the EEG. This study aimed to examine this distinction in normal children during the performance of processing tasks.

Methods: EEG, skin conductance level (SCL) and non-specific skin conductance responses (NS-SCRs) were recorded in 20 normal children (14 boys and 6 girls) during resting eyes-open, drawing, reading and mathematics conditions. The EEG data were Fourier transformed to provide estimates for total power and absolute and relative power. The theta/beta ratio was also calculated.

Results: Absolute and relative alpha decreased, and frontal midline absolute delta and theta, posterior absolute beta, SCL and NS-SCRs increased from baseline to task performance. The drawing task had reduced absolute delta and increased posterior absolute beta compared to the reading and mathematics tasks. The reading task had increased posterior absolute theta and alpha compared to the mathematics task.

Discussion: These results indicate clear arousal and activation differences between tasks. However, it remains inconclusive as to whether the theta/beta ratio reflects arousal or activation. The implications of these results in relation to syndromes such as Attention-Deficit/Hyperactivity Disorder will be discussed.

Email: cm75@uow.edu.au

An ERP study of response inhibition in nonclinical obsessive-compulsive adults

Val Markovska and Stuart J. Johnstone
Brain & Behaviour Research Institute and Department of Psychology, University of Wollongong, Wollongong, Australia

Introduction: Obsessive-compulsive disorder (OCD) is a debilitating anxiety disorder characterised by obsessions and compulsions. Considerable evidence suggests that a disruption in executive functioning, specifically inhibitory processing, contributes to OCD. This study examined response inhibition in a nonclinical university population. Differences in behavioural performance and ERP components, particularly N2 and P3, were predicted.

Methods: In phase one, obsessive-compulsive characteristics (OCC) were measured in 193 participants using the OCI-R, a self-report questionnaire for assessing obsessive-compulsive symptoms. In phase two, thirty-four subjects were selected based on extreme OCI-R scores and divided into High and Low OCC groups. ERPs were recorded while subjects participated in a visual Go/Nogo task with varying numbers of Go stimuli presented before Nogo stimulus.

Results: The ability to inhibit a response was significantly reduced in the High OCC group with additional response priming. ERPs revealed group differences in early sensory and late slow wave components. P2 and N2 varied in both groups with priming, while no effects were found for the P3.

Discussion: The results indicate that both behavioural and ERP differences can be found in nonclinical subjects. The study offers support to the inhibitory hypothesis by demonstrating such deficits are related to obsessive-compulsive characteristics independent of clinical diagnosis.

Email: vm175@uow.edu.au

EEG in children with Attention-Deficit/Hyperactivity Disorder and comorbid internalising disorders (anxiety/depression)

Lynne M. Mason, Robert J. Barry and Adam R. Clarke
Brain & Behaviour Research Institute and Department of Psychology, University of Wollongong, Wollongong, Australia

Introduction: Attention-Deficit/Hyperactivity Disorder (AD/HD) has a high level of comorbidity with other developmental disorders such as learning difficulties, disruptive behaviour disorders, and internalizing disorders e.g., anxiety/depression. Internalizing disorders are known to occur in 13% to 50% of children with AD/HD and there is evidence that comorbid AD/HD and internalizing disorder may be a distinct clinical subtype independent of “pure” AD/HD.

Methods: The present study used an eyes-open at rest condition to examine EEG in four groups of children (aged 5-16 years) with AD/HD-alone, Internalizing-alone, comorbid AD/HD+Internalizing, and normal controls.

Results: Consistent with previous findings we found that AD/HD was associated with increased theta and decreased beta, while AD/HD-alone was also associated with increased relative alpha, maximal at posterior sites. Children with internalizing disorders had a reduction in absolute alpha at posterior sites, and elevated absolute and relative beta, and relative theta. Both AD/HD-alone and Internalizing-alone had globally elevated relative alpha, and globally reduced relative beta, and regional differences in theta and delta. These effects did not add together in the comorbid AD/HD+Internalizing group.

Discussion: These results provide additional neurophysiological support for the view that the cormorbid AD/HD+Internalising group is a distinct subtype of AD/HD.

Email: lmmason@bigpond.net.au

Does unattended duration-MMN latency reflect streaming or averaging?

David N. McKenzie and Robert J. Barry
Brain & Behaviour Research Institute and Department of Psychology, University of Wollongong, Wollongong, Australia

Introduction: The necessity of attention for auditory streaming is debated. We sought evidence that unattended sound sources are not streamed but rather form a collective unattended sound representation.

Methods: In the 2-Stream condition 19 participants attended one of two simultaneous rapidly presented streams of 80 ms sounds [Left ear (2000 Hz, 70 dB SPL) and Right ear (800 Hz, 85 dB SPL) alternating with 140 ms SOA]. Occasional duration deviants (120 ms) presented to both ears evoked attended and unattended duration-MMN. In the 4-Stream condition an additional stream of shorter (40 ms) sounds was added to each ear (Left: 2350 Hz, 70 dB SPL; Right: 660 Hz, 85 dB SPL) without additional deviants. Participants again attended one 2-Stream sound source. If these additional short unattended sounds merge with a collective unattended sound representation, this condition should produce earlier unattended duration-MMN than the 2-steam condition.

Results: Attention reduced MMN latency significantly. Right ear reduction was greater in the 2- than 4-Stream condition but reflected both unattended latency reduction and an unexpected attended latency increase. A similar left ear tendency was non-significant.

Discussion: These ambiguous results may reflect floor effects stemming from the reported ~70 ms minimum duration-MMN onset latency.

Email: dnm54@uow.edu.au

Abnormal recruitment of working memory updating networks in PTSD

Kathryn A. Moores,1 C. Richard Clark,1 Alexander C. McFarlane,2 Greg C. Brown,3 Aina Puce4 and D. James Taylor3

1School of Psychology, Flinders University, Adelaide, Australia
2University of Adelaide, Adelaide, Australia
3Royal Adelaide Hospital, Adelaide, Australia
4Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, West Virginia, USA

Introduction: Post-traumatic stress disorder (PTSD) is characterised by disturbances in concentration and memory. Abnormalities in working memory (WM) systems have previously been found in PTSD (Clark et al., 2003), although the specificity of this finding is unclear. This study aimed to clarify the nature of WM dysfunction in PTSD by investigating several aspects of WM updating function, including updating of verbal stimulus material, organisation of contingent planned responses, and WM maintenance operations in PTSD.

Methods: Functional MRI data were recorded from 13 PTSD patients and matched controls during the performance of WM and visual fixation tasks. During the WM task, participants updated either perceptual (stimulus set) or behavioural (response set) representations, or did not update WM (maintenance). Random effects analyses were employed to identify abnormal patterns during these processes in PTSD.

Results: fMRI results appeared to indicate a pervasive reduction in brain activity during WM (stimulus set) updating. However, further analyses instead suggested abnormal recruitment of WM updating networks during WM maintenance operations in PTSD. In contrast, updating response set was normal in PTSD.

Discussion: Findings suggest compensatory recruitment of WM updating networks during WM maintenance operations in PTSD. The findings indicate verbal sensitivity to WM abnormalities in PTSD.

Email: Kathryn.Moores@flinders.edu.au

The effects of progressive muscle relaxation on the correlates of anxiety in self-reporting exam-anxious students

Robyn Moroney1,2 and Robert J. Barry1

1Brain & Behaviour Research Institute and Department of Psychology, University of Wollongong, Wollongong, Australia
2School of Nursing, Family and Community Health, University of Western Sydney, Penrith South, Australia

Introduction: Progressive Muscle Relaxation (PMR) was investigated as a treatment of exam anxiety, and effects were monitored using autonomic measures.

Methods: An ambulatory monitoring system was used to individually monitor 20 volunteers who self-reported as exam-anxious, while they undertook oral examinations as part of their undergraduate degree. Heart rate (HR) and skin conductance level (SCL) were recorded in a baseline condition, and before/during/after two subsequent exams. Between exams subjects were randomly allocated to control (N=10) and treatment (N=10) groups. The treatment group was instructed in PMR and received a personal PMR audio cassette programme. State and trait anxiety inventories were administered at baseline, and trait anxiety at each exam.

Results: Both HR and SCL showed significant increases from baseline to the exam situation which did not differ between groups. HR and SCL levels were lower in exam 2 than in exam 1 and this appears to be due to the treatment, with a significant exam x treatment interaction in both measures. State anxiety paralleled the autonomic measures.

Discussion: This study shows that a PMR treatment is effective in reducing both reported anxiety and autonomic correlates of stress/anxiety of exam-anxious individuals in a real-life exam situation.

Email: r.moroney@uws.edu.au

ERPs dissociate the effects of switching task-sets and task-cues

Rebecca Nicholson, Frini Karayanidis, Elizabeth Bumak, Dane Poboka and Patricia T. Michie
Functional Neuroimaging Lab, School of Behavioural Sciences, University of Newcastle, Callaghan, Australia

Introduction: Recent studies have suggested that reaction time (RT) costs associated with switching tasks reflect a cue repetition benefit rather than an endogenous control process of task-set reconfiguration (Logan and Bundesen, 2003). The current study aimed to dissociate the contribution of cue processing and task-set reconfiguration processes to behavioural and ERP indices of task-switching.

Methods: Participants randomly switched between two simple tasks. Task was cued 600 ms prior to stimulus presentation using either a colour or shape cue.

Results: A significant RT task switch cost was found when controlling for either a repeat or switch in cue category. In comparison, a switch in cue category had no effect on RT, even when examined across a cumulative distribution. Electrophysiological data revealed early cue processing effects within the first 300 ms after cue onset. However, replicating previous findings, an increased parietal positivity was found for task switch trials that emerged prior to stimulus onset.

Discussion: This suggests task-set reconfiguration processes are activated when switching between tasks and supports the usefulness of task-switching paradigms in investigating cognitive control processes.

Email: rebecca.nicholson@newcastle.edu.au

Localisation of anticipatory task-switching processes

Rebecca Nicholson, Frini Karayanidis, Ross Fulham, Patricia T. Michie
Functional Neuroimaging Lab, School of Behavioural Sciences, University of Newcastle, Callaghan, Australia

Introduction: Previous studies have shown a differential positivity occurring in anticipation of a switch in task. The current study aimed to further examine the underlying structure of this positivity through the use of independent component analysis (ICA) and low-resolution electromagnetic tomography (LORETA).

Methods: Participants randomly switched between two simple tasks, as controlled by the experimenter. A cue was presented 600 ms prior to stimulus onset, which indicated whether the next trial required a switch or repeat in task. EEG data were recorded from 64 channels with digitised electrode locations.

Results: Consistent with previous studies, switch compared to repeat trials were associated with increased reaction time and greater parietal positivity. ICA was conducted separately for switch versus repeat trials up to 700 ms after cue onset. There were three similar components for both trial types. LORETA analysis showed that, following presentation of the cue, switch relative to repeat trials were associated with greater activation in the prefrontal cortex and precuneus.

Discussion: These findings suggest that switch and repeat trials have similar underlying component structures. The increased prefrontal activation on switch trials may reflect cognitive control processes involved in task-set reconfiguration, while the parietal activation may reflect the preparation of response-stimulus mappings.