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

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N2 versus P3 as a marker of inhibitory processing in a visual Go/NoGo task: An exploration in social drinkers

Bruce W. Oddy, Robert J. Barry, Stuart J. Johnstone and Adam R. Clarke
Brain & Behaviour Research Institute and Department of Psychology, University of Wollongong, Wollongong, Australia

Introduction: The question of which of N2 or P3 is a marker of inhibition in the warned Go/NoGo task was explored in social drinkers.

Methods: EEG data were recorded from two extreme drinking-level groups (each N = 13), averaged, subjected to a PCA with varimax rotation procedure to allow correction for the CNV (see Oddy et al., 2005), and then N2 and P3 amplitudes were analysed with an ANOVA over Go/NoGo conditions and group.

Results: The light social drinkers (< 9 standard drinks/month) differed significantly from the heavy social drinkers (> 30 standard drinks/month) on alcohol consumption and impaired control, but not on age, state/trait anxiety; depression, locus of control, reaction time, or errors. No group X condition interactions were found in N2, but a significant group X condition interaction indicated a reduced frontal enhancement of the NoGo P3 in heavy drinkers.

Discussion: At first glance these data support the P3 as a marker of inhibitory function. However, the lack of performance differences between the groups suggests that inhibitory factors may not be the main contributor to the differences found with the anteriorisation of the NoGo P3. An interpretation within the framework of the orienting reflex is offered.

Email: bwo01@uow.edu.au

Improvement of Baroreceptor Effectiveness Index after 15-weeks of exercise training

Young J. Park, Justin Jones and Stephen H. Boutcher
School of Medical Sciences, University of New South Wales, Sydney, Australia

Introduction: In healthy individuals, progressive increase or decrease in systolic blood pressure (SBP) is not always followed by baroreflex-driven lengthening or shortening of the RR interval (RRI). How exercise training influences this phenomenon is undetermined. Thus, the effects of 15-weeks of exercise training on baroreflex effectiveness index (BEI) in healthy young females was examined.

Methods: Females (22.5±0.7 yr) were assigned to a 15-week (3 times per week) supervised exercise training program (n=9) or a control group (n=9). Before and after (pre/post design) the 15-week training program, maximal oxygen uptake, and body composition were determined. Cardiovascular response to the Stroop Colour-Word Task (Stroop) were also determined. BEI was computed as the ratio between the number of SBP ramps followed by a concomitant reflex RRI modulation and the overall number of SBP ramps from 5 min of supine resting and 5 min of Stroop.

Results: Maximal oxygen uptake increased significantly (P<0.05) and percent of body fat decreased significantly (P<0.05) after the training program. BEI determined during Stroop significantly increased (P<0.05), however, there was no difference in BEI during supine rest.

Discussion: These results show that an exercise training program increases spontaneous baroreflex control of the heart during Stroop performance.

Email: yj.park@student.unsw.edu.au

The effects of MR scanner noise on auditory thresholds: A psychoacoustic study using SAM white noise, pure tones, and complex tones

Bryan K. Paton, Madeleine Hinwood and Timothy W. Budd
School of Behavioural Sciences, University of Newcastle, Callaghan, Australia

Introduction: For many auditory fMRI studies MR gradient noise generated during EPI scanning interferes with perception of auditory stimuli and therefore blood oxygen level-dependent (BOLD) activity. This study examined the extent to which EPI scanner noise differentially influences detection thresholds for different classes of acoustic stimuli and whether this masking is influenced by headphone type.

Methods: Using a MRI scanner simulator, thresholds for pure tone, complex tone and sinusoidally amplitude modulated (SAM) white noise stimuli were estimated using a 2IAFC psychophysical procedure. Thresholds were estimated with and without the presence of simultaneous scanner noise and for two headphone types (intra-aural/circum-aural) and submitted to a 2x2x3 repeated measures within subject GLM ANOVA.

Results: There was a significant effect of gradient scanner sounds on all signals with a significant difference between both tone conditions and the SAM condition, F(1.37, 19.15) = 16.74, p < .01. No significant difference was found between the pure and complex tone conditions. The intra-aural earphones demonstrated superior scanner noise attenuation characteristics, F(1, 14) = 13.19, p = .003, compared to circum-aural earphones.

Discussion: The results highlight the differential impact of acoustic masking by EPI scanner noise for different classes of acoustic stimuli and indicate that this effect may be modified by headphone type.

Email: Bryan.Paton@newcastle.edu.au

Auditory oddball in two subtypes of Attention-Deficit/Hyperactivity Disorder: An investigation of age

Sharnel Perera, David Crewther, Hannah A. D. Keage, C. Richard Clark, Daniel F. Hermans, Leanne M. Williams and Evian Gordon
Brain Sciences Institute, Swinburne University of Technology, Hawthorn, Australia

Introduction: The oddball paradigm is a well documented method of investigating attentional functioning by assessing brain activity. Previous research has found AD/HD individuals perform poorly on oddball tasks compared to Controls. Utilising an oddball task, we aimed to investigate behaviour, ERPs, and associated age-related changes in AD/HD-in and AD/HD-comb compared to Controls.

Methods: The Brain Resource Company battery of psychophysiological tasks was performed on 91 children and adolescents diagnosed with AD/HD (41 AD/HD-in, 50 AD/HD-comb). Their data was compared with 238 matched controls. Reaction time, reaction time variability, false positives, false negatives, and total errors to targets in a two-tone oddball task were obtained. Data from scalp sites Fz, Cz, Pz are presented.

Results: Increasing behavioural impairment with age was apparent in both clinical groups, though more pronounced in AD/HD-comb. Comparatively greater deficits in ERPs were seen in AD/HD-comb than AD/HD-in relative to Controls. Age-related ERP improvement was seen in Controls, though to a lesser degree in the AD/HD groups.

Discussion: Behavioural and ERP deficits were more pronounced in the ADHD-comb group relative to both ADHD-in and Controls, indicating impaired cognitive processing of salient stimuli which corresponds with the lack of adequate improvement both behaviourally, and in ERPs with age.

Email: ShPerera@groupwise.swin.edu.au

The effects of an extract of Pinus radiata pine bark (Enzogenol®) on cognitive function in individuals at risk of cognitive decline

Andrew Pipingas, Richard. B. Silberstein, L. Vitetta, C. Van Rooy, J.V. Nastasi and A. Sali
Brain Sciences Institute, Swinburne University of Technology, Hawthorn, Australia

Introduction: Dietary supplementation with plant extracts rich in flavonoids is becoming very popular for its potential health benefits. The physiological effects of such extracts can be complex, and deserve thorough investigation ideally by controlled clinical trials. This study investigated effects of supplementation with a Pinus Radiata bark extract (Enzogenol®) and vitamin C (vitC) on cognitive function in a group of subjects at risk of cognitive decline. Based on our previous findings of significant age-related decline in spatial working memory, we hypothesized that spatial working memory performance would improve with Enzogenol.

Methods: Forty two men (50-65 years) with a body mass index greater than 26 were enrolled in the study. Participants were randomly assigned to two groups. Supplementation was with either Enzogenol + vitC or with vitC only. Participants performed a battery of computerised cognitive tasks prior to commencement with supplementation and then again after 5 weeks.

Results: Speed of response increased for the spatial working memory task following Enzogenol + vitC supplementation (p<0.005) but not vitC only supplementation. Effects of supplementation on other cognitive tasks are discussed.

Discussion: It is suggested that Enzogenol may improve spatial working memory and may act to reduce the deleterious effects of ageing on cognition.

Email: apipingas@swin.edu.au

Gamma oscillations and visual binding

Peter A. Robinson
School of Physics, University of Sydney, Sydney, Australia

Introduction: At the root of visual perception is how the brain analyzes features in a scene and binds related ones together. This process is closely associated with oscillations of brain activity in the gamma band. Gamma oscillations at different sites are often correlated, with a peak correlation function (CF) at zero lag, implying simultaneous firing even for large conduction delays. Correlations are strongest between areas stimulated by related features. We calculate these properties from the physiology of primary visual cortex (V1).

Methods: Neural activity supported by mm-scale patchy interconnections in V1 is modeled using mean-field theory. Predicted gamma wave properties and CFs are compared with published data from a variety of animal experiments.

Results: Gamma responses to stimuli are calculated and shown to reproduce experimental findings, including associations between oscillations and zero-lag synchrony, connections with feature preferences, and variations of CFs with attention. Gamma waves obey the Schroedinger equation, opening the possibility of cortical analogs of quantum phenomena. Also cellular receptive field properties affect the zero-lag peak.

Discussion: The results show that it is possible to calculate gamma properties from physiology of patchy connections in V1, thereby providing a foundation to explore how they relate to visual binding.

Email: robinson@physics.usyd.edu.au

Preattentive emotional processing in depression

Bianca Romanyk, Rodney J. Croft, Greg Murray and Natalie Krapivenski
Brain Sciences Institute, Swinburne University, Hawthorn, Australia

Introduction: In general, negative valance stimuli are more salient than neutral, attracting more attention and enhancing processing. The ‘cognitive motivational model’ (CMM) of depression predicts that the disorder is not associated with abnormal valance-related processing biases at the preattentive level. In order to test the CMM, this study measured valence-related preattentive processing biases in depressed patients, employing as its index the P100 event-related potential (ERP) to pleasant, neutral and unpleasant visual stimuli.

Methods: 13 depressed patients and 13 age- and gender-matched controls were presented with emotive photographs (matched for arousal) from the International Affective Picture System. ERPs were extracted using a combination of standard and PCA techniques, with P100 amplitudes compared across category and group.

Results: Overall, P100 amplitude was enhanced to both pleasant and unpleasant stimuli (relative to neutral). The enhanced P100 amplitude to unpleasant stimuli did not differ between the groups, whereas the enhanced P100 to positive stimuli was more pronounced (trend level) in patients.

Discussion: Our findings support predictions made by the CMM that depression is not related to abnormalities in preattentive negative processing, whereas some support was found for the role of pre-attentive positive biases. These conclusions remain speculative due to methodological constraints of the study.

Email: Bianca_romanyk@hotmail.com

Phasic and tonic measures of the OR in an auditory dishabituation paradigm: Electrodermal activity and event-related potentials

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

Introduction: We examined putative CNS indices of tonic and phasic aspects of the OR in an event-related potential (ERP) dishabituation paradigm. Skin conductance level (SCL) and skin conductance response (SCR) were used as the tonic and phasic OR “yard-sticks”. Their stimulus-response patterns were compared with those of two ERP components, the contingent negative variation (CNV) and the late positive complex (LPC).

Methods: EEG and SCL were simultaneously recorded from 36 subjects. Prestimulus SCLs were taken as measures of arousal level at each stimulus presentation and SCRs were derived for the 1 - 3 s poststimulus period. CNV was defined as the difference between mean amplitude of a 500 ms segment of the prestimulus period (-2500 to -2000 ms) and the baseline period (-100 to 0 ms), and the LPC was defined as the most positive peak occurring between 260 and 650 ms poststimulus.

Results: The LPC showed a stimulus-response pattern across trials identical to that of the SCR. Arousal changes indexed by the SCL were paralleled in the CNV, but in addition, an expectancy effect was shown by the CNV that was not apparent in the SCL.

Discussion: This study clarifies links between the autonomic OR and its CNS correlates.

Email: jrushby@uow.edu.au

Spatial coordinate systems within the parietal lobes: Localization of a cognitive spatial map in humans

Shaun Seixas,1 Peter Brotchie,2 David Crewther1 and Shoane Ip1

1Brain Sciences Institute, Swinburne University, Hawthorn. Australia
2Barwon Medical Imaging: Geelong Hospital, Geelong, Australia

Introduction: Human and animal behavior during navigation suggests the existence of a cognitive spatial map of the environment. The discovery of “place cells” within the rat hippocampus has convinced many that the hippocampus is the site of the cognitive spatial map. However, clinical observation is inconsistent with this view, indicating that the parietal lobes are a more likely site. Therefore the aim of this study was to further investigate the role of the parietal lobes in spatial mapping.

Methods: Nine, female participants, aged 18-24 years were trained to navigate to a single known target destination within a virtual 3D environment containing a single visual landmark. Two perturbations of the initial starting location (control condition) were interleaved within this task. Functional MRI was used to assess increases in activity, reflecting the updating of spatial map information. Statistical parametric maps were derived for the contrast of the perturbed conditions versus the control condition.

Results: Increases in BOLD signal were found within the parietal cortex bilaterally and deep within the intraparietal sulcus when perturbed conditions were compared to the control condition.

Discussion: Functional activity observed within the parietal lobes during this task adds support to the notion of a spatial map being held within the parietal lobes.

Email: sseixas@swin.edu.au

Auditory hallucinations in psychosis: Neural “release” in the substrates of episodic verbal memory and central auditory processing

Alex A. Sergejew,1,2,3 David Copolov,2 Melissa Wright,2 Tracey Shea3 and Gary Egan3

1Maroondah Hospital, Ringwood East, Australia
2Mental Health Research Institute of Victoria, Parkville, Australia
3Centre for Neuroscience, Howard Florey Institute, University of Melbourne, Parkville, Australia

Introduction: Our novel model of the neurobiological basis of auditory-verbal hallucinations (AHs) in psychosis conceptualises these phenomena as driven by neurological “release” in the substrates of episodic verbal memory and central auditory processing. Converging fMRI and EEG evidence suggests altered effective connectivity in these substrates, however our model makes specific trait versus state-based predictions.

Methods: Effective connectivity in these circuits was quantified using information-theoretic analyses of EEG recordings, and compared between groups of psychotic patients with and without AHs and a group of normal controls.

Results: As predicted, connectivity was significantly reduced in the AH group compared to clinical and normal controls. Moreover, hallucinations were observed to be associated with increased connectivity compared to non-AH states.

Discussion: This finding is interpreted as predisposing individuals with AHs to CNS “release” in these circuits, and is regarded as strongly consistent with the postulated “release.” Contemporary neurocognitive models of AHs are briefly reviewed in light of these new findings.

Email: aas@asp.org.au

Emotional prosodic processing and source monitoring in auditory hallucinations

Tracey L. Shea,1,2 Alex A. Sergejew,1,2 G.F. Egan,1,3 D. Burnham,4 David L. Copolov1,5

1Mental Health Research Institute of Victoria, Australia
2Centre for Neuroscience and 3Howard Florey Institute, University of Melbourne, Parkville, Australia
4MARCS Auditory Laboratories, University of Western Sydney, Bankstown, Australia
5Department of Psychiatry, University of Melbourne, Parkville, Australia

Introduction: The misattribution theory of auditory hallucinations (AHs) proposes that AHs arise because patients misattribute internal cognitive events to an external source. Mechanisms of misattribution have yet to be elucidated, but Cutting (1990) speculated that deficits of emotional prosody (EP) may lead patients to be unable to recognise AHs as belonging to the self. We hypothesised that hallucinators would demonstrate greater deficits in source monitoring (SM) and EP than non-hallucinators and controls.

Methods: Participants completed a SM task comprising two word lists generated by participant and experimenter. They were tested on their ability to monitor the origin of these items. They also listened to a series of neutral sentences expressed in happy, sad and neutral voices and rated the vocal emotion of each sentence.

Results: Deficits were observed for patient groups compared to controls, with trends for hallucinators to perform more poorly than non-hallucinators. Participants with higher EP scores tended to have higher SM scores.

Discussion: The trend for participants to perform similarly on both the SM and EP tasks lends support to Cutting’s proposal that emotional prosodic processing might play a role in the misattribution of AHs. However, further testing is needed to clarify this relationship.

Email: t.shea@pgrad.unimelb.edu.au

Brain functional connectivity correlates of performance on the Continuous Performance Task in boys diagnosed with Attention Deficit Hyperactivity Disorder (ADHD)

Richard B. Silberstein,1,2 Maree Farrow3 and Paul L. Nunez4

1Brain Sciences Institute, Swinburne University of Technology, Hawthorn, Australia
2Howard Florey Institute of Experimental Physiology and Medicine, Parkville, Australia
3Department of Psychology, Monash University, Melbourne, Australia
4Brain Physics Inc., San Diego, California, USA

Introduction: We examined the relationship between brain functional connectivity and performance (RT) when a boys newly diagnosed with ADHD (N=60) and a normal control group (N=31) perform the AX version of the continuous performance task (CPT-AX). The ADHD group performed the tasks before and after the administration of an oral dose of methylphenidate (MPD).

Methods: The steady state visually evoked potential (SSVEP) was elicited by a 13 Hz uniform visual flicker superimposed over the visual fields and the SSVEP event-related partial coherence, a measure of functional connectivity, was calculated for all electrode pairs over a 10 sec epoch for all correct responses. We determined the correlation coefficient between cortical connectivity and individual RT when subjects performed the CPT-AX.

Results: The number of electrode pairs where RT and connectivity were correlated peaked following the appearance of the X, and these were located at frontal-prefrontal sites. Importantly, all connectivity measures were positively correlated with RT. We also found that MPD induced reductions in RT were associated with reductions in functional connectivity at frontal-prefrontal sites following target detection.

Discussion: We speculate that ADHD related performance and cognitive deficits may be a consequence of the failure to effectively suppress or decouple irrelevant functional connectivity.

Email: rsilberstein@swin.edu.au

Response preparation and inhibition in an auditory warned frequent-Go/rare-NoGo task

Janette L. Smith, Stuart J. Johnstone and Robert J. Barry
Brain & Behaviour Research Institute and Department of Psychology, University of Wollongong, Wollongong, Australia

Introduction: An increased frontal N2 and P3 are typically observed when inhibition is required in the Go/NoGo task. The current study investigates the functional significance of these components by examining their relationship to prior response preparation.

Methods: Forty-four adult participants completed a warned Go/NoGo task with 70% Go stimuli. A within-subject median-split of RT on Go trials allowed topographic analysis of pre- and post-S2 components associated with Fast and Slow Go responses. Additionally, a median-split of NoGo trials on the preceding late CNV allowed investigation of inhibitory components and their relationship with response preparation.

Results: The late CNV was the only pre-S2 component to differ between Fast and Slow trials, and the only significant contributor to RT in regression analyses. In Go/NoGo comparisons, the usual N2 and P3 effects were observed. However, only the NoGo P3, not the NoGo N2, was larger after high levels of preparation. The NoGo N2 effect was also unrelated to the late CNV in regression analyses.

Discussion: The NoGo N2 effect does not appear to reflect inhibition; rather, the NoGo P3 may reflect this process.

Email: janette.smith@unsw.edu.au

Event-related potentials in obsessive-compulsive disorder during an emotional Stroop task

Sue J. Thomas, Craig J. Gonsalvez and Stuart J. Johnstone
Brain & Behaviour Research Institute and Department of Psychology, University of Wollongong, Wollongong, Australia

Introduction: Attentional biases towards anxiety-related information are assumed by cognitive models to be important in the symptomatology of obsessive-compulsive disorder (OCD). A common instrument for measuring such biases is the emotional Stroop task, which employs no direct measure of attention to threatening stimuli, but infers the presence of its preferential processing based on response time (RT) impairment in a competing task. RT studies of the emotional Stroop task have been inconclusive with regards to attentional biases in OCD. Event-related potential (ERP) measures allow more direct examination of attentional biases in anxiety.

Methods: Twelve individuals with OCD, and 22 healthy students participated. ERPs and RTs to threat and neutral words were recorded during two tasks (colour relevant, in which the colour ink of words was identified, and word relevant in which words were classified as threatening or not).

Results: Between group differences were observed in ERPs to threat-neutral stimuli. Additionally, ERPs to threat compared to neutral stimuli in healthy controls were characterised by higher P3 amplitudes despite an absence of differentiation by RT measures.

Discussion: ERPs provide valuable additional information about attention in emotional Stroop tasks. The patterns of differences between OCD and normals, and their clinical implications, will be discussed.

Email: sue_thomas@psyc.uow.edu.au

Motor unit activity in the upper airway dilator muscle genioglossus during sleep onset

John Trinder,1 Vanessa Wilkinson,1 Christian Nicholas,1 Christopher Worsnop,1 Simon Gandevia,2 Amy Jordan,3 Atul Malhotra,3 Kathryn Steiner3 and David White3

1Department of Psychology, University of Melbourne, Parkville, Australia
2University of NSW, Sydney, Australia
3Harvard Medical School, Harvard, USA

Introduction: Genioglossus (GG), the major protrudor muscle of the tongue, is critical in the maintenance of pharyngeal patency during sleep. While GG motor units (MUs) show a variety of discharge patterns, the contribution of different discharge patterns to total muscle activity during sleep remains unknown. We assessed the effect of sleep onset (SO) on tonically active (TT) and inspiratory phasic (IP) GG MUs.

Methods: Data were collected on 5 healthy subjects (3M and 2F). Motor unit activity in GG was assessed by monopolar intramuscular 112µm Teflon coated wire electrodes. Three electrodes were inserted into the muscle using a percutaneous approach, guided by ultrasonography. 34 SOs with 70 MUs were identified.

Results: 16 MUs were classified as TT units and 38 as IP units. The discharge rates of TT units decreased by an average of 2.6% (SD=10.1)(9 increased, 7 decreased). IP units fell by 67% (SD=35.9)(none increased and 13 stopped completely). Further, there was a significant correlation (r=.58, p<.05) between the degree to which a unit was phasic and the magnitude of the unit’s reduction in firing rate at sleep onset.

Discussion: Tonic and phasic MUs are differentially affected by changes in sleep-wake state.

Email: johnat@unimelb.edu.au

The effects of prefrontal 1 Hz RTMS on the EEG during an auditory odd-ball task: A pilot study of cortical plasticity in schizophrenia

Daniel Upton,1 Nicholas Cooper,1 Rebecca Segrave,1 Robin Laycock,1 Jayashri Kulkarni,1 Rodney Croft,2 Paul B. Fitzgerald1

1Alfred Psychiatry Research Centre, Department of Psychological Medicine, Monash University, Melbourne, Australia
2Brain Sciences Institute, Swinburne University of Technology, Hawthorn, Australia

Introduction: A growing body of evidence suggests that abnormal plasticity is a feature of schizophrenia. Transcranial magnetic stimulation (TMS) is a non-invasive form of brain stimulation with the capacity to modulate brain activity and function. Previous research in our lab has shown that repetitive (r)TMS of motor and premotor cortex lowers the resting motor threshold (RMT) in healthy individuals. Further, these changes were significantly attenuated in participants with schizophrenia. The present study describes the effects of prefrontal rTMS on control participants, as measured by the EEG.

Methods: 18 normal participants received 15 minutes of 1 Hz rTMS. Right and left dorsolateral prefrontal cortex (DLPFC) was stimulated on different occasions for each participant. The EEG was recorded during an auditory odd-ball task and analysed to determine event related potential (ERP) and event related desynchronisation (ERD) parameters.

Results: In the beta frequency band, a significant interaction between rTMS, side of stimulation and sagittality (frontal) was found.

Discussion: These results will be discussed in terms of beta ERD/S models of brain activation and inhibition. Specifically, the capacity of rTMS to modulate this index of brain activity and its suitability to explore prefrontal plasticity in schizophrenia will be addressed.

Email: d.upton@alfred.org.au

Traditional and model-based approaches to assessing the reproducibility of the EEG

Sacha J. van Albada, C. J. Rennie and Peter A. Robinson
School of Physics, University of Sydney, Sydney, Australia
Brain Resource Company, Sydney, Australia

Introduction: A recently developed physiology-based EEG model (Robinson et al., 2005) provides us with means for assessing inter- and intra-individual differences (between sessions) in spectra, complementary to qEEG measures such as band powers, spectral entropy, and peak frequencies.

Methods: Eyes-closed Cz-spectra collected at various intervals over the course of a year were analyzed using qEEG measures, for which inter- and intra-individual variances were determined versus time. Spectra were also fitted to a model of EEG activity, the corresponding parameters determined, and investigated for changes over time.

Results: Individual variance in model parameters was found to be 58 ± 11 % of the population variance; that in qEEG measures 26 ± 17 %. The characteristic time scale for variations was less than a week. Whereas subjects differed significantly from the population mean in all model parameters, only two parameters showed a significant time trend (p < .05).

Discussion: The relative constancy of model parameters implies that a similar amount of information about underlying physiology can be gained from a single EEG recording as from repeated sessions. The proportion of variance accounted for by intra-individual differences helps to determine whether an individual differs significantly from the population mean on any particular measure.

Email: albada@physics.usyd.edu.au

Topography of visuo-verbal event-related potentials during a sustained attention/working memory-updating task in posttraumatic stress disorder

Melinda Veltmeyer,1 Richard Clark,1 Sandy McFarlane,2 Richard Bryant3 and Evian Gordon4

1Department of Psychology, Flinders University of South Australia, Adelaide, Australia
2University of Adelaide and Department of Psychiatry, Royal Adelaide Hospital, Adelaide, Australia
3University of New South Wales, Sydney, Australia
4Brain Resource Company, Sydney, Australia

Introduction: Deficits in memory and attention are commonly reported in PTSD. The present study investigated the neural bases of these deficits using ERPs. Testing involved a visuo-verbal task that required working memory updating during sustained attention.

Method: 34 people with PTSD and 136 age and gender matched controls completed a visuo-verbal “two-in-a-row” paradigm. P300 ERPs to targets and background stimuli (working memory updating) were compared between groups.

Results: ERPs to background stimuli were reduced in PTSD relative to controls over the right parietal and occipital regions, consistent with Posner’s proposed “posterior activation network”, while ERPs to target tones were reduced over the right frontal/anterior temporal region. Interestingly, the two patterns of abnormality were negatively related, Right posterior background ERPs were negatively related to clinical arousal, as measured by the clinician-administered PTSD scale. The latter ERP abnormality was paradoxically associated with reduced depression and stress scores, but increased derealization.

Discussion: The significance of these findings is discussed in terms of current neurobiological theories of PTSD.

Email: melinda.veltmeyer@flinders.edu.au

When alpha power goes up, must frequency come down? An investigation of arousal and its connection with EEG alpha

Paris Waters, Joanne Ayoub, Robert J. Barry, Jacqueline A. Rushby and Carlie A. Lawrence
Brain & Behaviour Research Institute and Department of Psychology, University of Wollongong, Wollongong, Australia

Introduction: Investigated independently, arousal has been found to exhibit a significant inverse relationship with alpha power and a significant direct relationship with alpha frequency (Barry, et al., 2004; Barry, et al., 2005). The purpose of this investigation was to investigate and attempt to replicate these findings using adult participants.

Methods: We recorded SCL and EEG activity in 40 adult participants. Subjects were asked to relax with their eyes closed for two, three minute periods which were separated by a cognitive ERP task.

Results: SCL correlated directly with alpha frequency and inversely with alpha power. However, alpha power at O1 and SCL was the only significant correlation found.

Discussion: In adult participants, arousal was related to alpha power and frequency in the predicted directions. However, few significant correlations were obtained and our original hypotheses were supported only partially. These findings extend our understanding of the interaction between arousal, as measured through SCL, and EEG alpha, and combined with findings by Barry et al. (2004), warrant further investigation of the interaction between arousal and lower alpha power.

Email: pw80@uow.edu.au

Brain maturation in adolescence: Concurrent changes in neuroanatomy and neurophysiology

Thomas J. Whitford,1,2 Christopher J. Rennie,1,3 Stuart M. Grieve,4 C. Richard Clark,5 Evian Gordon1,4,6 and Leanne M. Williams1,6

1The Brain Dynamics Centre, Westmead Hospital, Sydney, Australia
2School of Psychology, University of Sydney, Sydney, Australia
3Department of Medical Physics, Westmead Hospital, Sydney, Australia
4The Brain Resource Company, Sydney, Australia
5Cognitive Neuroscience Laboratory and School of Psychology, Flinders University, Adelaide, Australia
6Department of Psychological Medicine, University of Sydney, Sydney, Australia

Introduction: Adolescence to early adulthood is a period of dramatic transformation in the healthy human brain, however the relationship between the concurrent structural and functional changes remains unclear.

Methods: We investigated the impact of age on both neuroanatomy and neurophysiology in the same healthy subjects (n=138) aged 10 to 30 years, using magnetic resonance imaging (MRI) and resting electroencephalography (EEG) recordings. MRI data were parcellated into subcortical and cortical grey and white matter regions using voxel-based morphometry. EEG slow-wave, alpha and beta power were quantified.

Results: Cortical grey matter volume was found to decrease with age, with the greatest change occuring in adolescence. EEG activity, particularly slow-wave, showed the same curvilinear decline across corresponding cortical regions. An inverse pattern of curvilinearlly increasing white matter volume was observed.

Discussion: We suggest that the reduction in grey matter primarily reflects a reduction of neurites, and that a corresponding elimination of the number of active synapses is responsible for the observed reduction in EEG power.

Email: twhi4033@mail.usyd.edu.au

The mellow years? Changes in ERP and fMRI measures of neural response to emotion stimuli predict better emotional stability over age

Leanne M. Williams, Donna Palmer, Kerri Brown, Belinda J. Liddell and Evian Gordon
University of Sydney and Brain Dynamics Centre, Westmead Hospital, Westmead, Australia

Introduction: Emotional health tends to improve with age, and there is a shift towards more positive and less negative emotion, but the neural underpinnings are unknown. We examined emotional stability and corresponding brain function over early teens to late adulthood.

Methods: In 219 healthy individuals (12 to 79 years) the NEO-FFI was used to assess neuroticism. ERPs (all subjects) and fMRI (matched subset) were recorded in response to facial expressions of fear and happiness. We focused on temporal and medial fronto-central components, and on medial prefrontal, amygdala and basal ganglia regions of interest.

Results: Regression and ANOVA showed an improvement in emotional stability (less neuroticism) over age. For fMRI, medial prefrontal activity increased for fear, and decreased for happiness. Medial fronto-central ERPs showed the same pattern of change, which was further dissociated by time: N200 and P300 (180-450 ms post-stimulus) increased to fear, while P80 and N120 (within 150 ms) decreased for happiness. fMRI and ERP changes over age were significant predictors of the increase in emotional stability.

Discussion: Increasing emotional stability with age is due to a better adaptive balance in the prefrontal brain systems which regulate responses to potential threat versus pleasure, consistent with a model of emotional selectivity.

Email: lea@psych.usyd.edu.au

Modelling and investigation on thalamic activity

Huiying Wu, and Peter A. Robinson
School of Physics, University of Sydney, Sydney, Australia

Introduction: Some electroencephalographic (EEG) rhythms, particularly spindle oscillations, are generated in the thalamus, but the underlying mechanisms are still not clear. Experimental limitations and the deep-brain location of the thalamus make in vivo measurement of thalamic activity difficult.

Method: A physiologically based mathematical model is employed to analyse electrical activity of the thalamus and its substructures. Possible EEG resonances, particularly sleep spindle oscillations, are investigated, and conditions for these oscillations are obtained. Our results are then compared with published experimental findings in physiology.

Results: An isolated reticular nucleus cannot generate spindle oscillations but can do so together with relay cells. Local interneurons (LIs) can also generate spindles with thalamocortical relay cells. Self-connections within the reticular nucleus and between LIs have similar effects on activity, and facilitate spindle oscillations.

Discussion: Our result on the isolated reticular nucleus is consistent with in vitro experiments but contradicts some in vivo experiments in cats. LIs can promote and participate in spindle oscillations, in agreement with experiments. The roles of LIs and reticular nucleus are similar in spindle oscillations. In general, LIs can only have pure inhibitory effect on the relay cells, whereas reticular nucleus can have net excitatory effect via LIs.

Email: hui@physics.usyd.edu.au / robinson@physics.usyd.edu.au

Spatial and categorical memory show a double dissociation with magnocellular and parvocellular visual evoked potential components in a normal aging population

Tiam Yap,1 Andrew Pipingas,1 David Crewther,1 Norman Moore2 and Sally Li2

1Brain Sciences Institute, Swinburne University of Technology, Hawthorn, Australia
2Adult Mental Health Rehabilitation Unit, Sunshine Hospital, Melbourne, Australia

Introduction: It is widely accepted that the dorsal and ventral cortical streams contribute differentially to behaviours, such as spatial and categorical memory. The visual contribution to the dorsal stream is dominated by the magnocellular (M) pathway, while the parvocellular (P) input projects to the ventral stream. Multifocal visual evoked potentials (mfVEPs) allow separate measurement of M and P contributions. The aim of this study is to investigate the relationship shared by the visual pathways and memory processes.

Methods: Twenty-three healthy participants, aged 60-77 years, performed a battery of cognitive tasks, which included memory for spatial location and object identification. mfVEP N1 latencies for 1st (M) and 2nd (P) slices of the second order kernel responses were measured and correlated with memory variables.

Results: Strong correlations were found between M-latency / location memory and P-latency / categorical memory. Furthermore, a significant double dissociation was found between magnocellular and parvocellular VEP components, and spatial and categorical memory scores.

Discussion: We would argue that the M and P components of the mfVEP are retrogradely sensitive to changes in cognition related to dorsal and ventral streams. This double dissociation should be further investigated in cognitive decline, e.g. in individuals with mild cognitive impairment.

Email: tyap@swin.edu.au