Convenors: Robert J. Barry, Stuart J. Johnstone, Adam R. Clarke
Support team: Ann Barry, Samantha Broyd, Carlie Lawrence, Jacqueline Rushby
Scientific Committee: Robert Barry, Richard Clark, Adam Clarke, Rodney Croft, David Crewther, Stuart Johnstone, Ottmar Lipp, Frances Martin, Pat Michie, Norman Moore, Alex Sergejew, Leanne Williams
The 15th Annual Conference of the Australasian Society for Psychophysiology (ASP) was hosted by the Brain & Behaviour Research Institute at the University of Wollongong. Papers clearly demonstrated the broad range of research carried out in this branch of the neurosciences within Australia. Oral sessions focused on activation/arousal, psychiatric problems, fMRI, MMN, Attention-deficit/Hyperactivity Disorder, cognitive processing, autonomic measures, brain impacts of electromagnetic fields, EEG modelling, and basic ERP processes. These were supplemented by a wide-ranging evening poster session. The number of excellent presentations by early-career scientists points to a solid future for both the field in Australia, and ASP.
Exhibitors contributed four Compumedics Neuroscan Student Travel Awards and four ADInstruments Student Presentation Awards. Additional financial support was provided by the Department of Psychology and Faculty of Health and Behavioural Sciences, University of Wollongong.
Each submitted abstract was peer-reviewed by members of the Scientific Committee.
These are listed by alphabetical order of the first author’s surname. If the paper was not presented by the first author, the name of the presenting author is underlined.
Apparent travelling waves in scalp EEG reveal a decrease in slow-wave activity for ADHD across several experimental paradigms
1Science Division, Brain Resource Company, Sydney, Australia
2Faculty of Information Technology, University of Technology, Sydney, Australia
3Cognitive Neuroscience Laboratory, School of Psychology, Flinders University, Adelaide, Australia
4Adolescent Medicine and 5Brain Dynamics Centre, Westmead Hospital, Sydney, Australia
Introduction: We describe a new method for measuring event-related travelling waves (TWs) in EEG. TWs have previously been shown to change according to task demands, but they have not been systematically studied in clinical disorders.
Methods: EEG was recorded from 167 ADHD subjects and 175 matched controls at 26 electrode sites during an auditory oddball task, continuous performance task (CPT), and Go-NoGo task. These tasks tap basic sensory-motor processes, concentration and working memory, and behavioural inhibition, respectively. Wavelet analysis was used to estimate the phases in the EEG at 10 ms intervals over 30 frequencies (1-16 Hz). The relative phases were fit to model TWs, and the stimulus-locked average of the variance explained by the TW model was compared across groups. These results were contrasted to those for other disorders (vs. matched controls): first episode psychosis, post-traumatic stress disorder and Alzheimer’s disease.
Results: ADHD subjects showed less 1-2 Hz TW activity across all three tasks. This was most prominent for CPT 450 ms post-stimulus and for Go-NoGo inhibition at 150 ms, while for oddball targets, it was persistent post-stimulus. No other disorders showed this effect.
Discussion: The data suggest that fewer event-related low frequency TWs may be specific to ADHD.
Correlations between electrodermal activity and other ANS measures of arousal
Introduction: We aimed to examine the relationship between other potential ANS measures of arousal and SCL. Skin conductance level (SCL) is considered as the arousal ‘gold standard’ and has often been compared to other putative indices of physiological arousal, such as non-specific skin conductance responses (NS-SCRs), heart rate (HR), blood pressure (BP), and respiration rate (RR). Arousal and activation have been used interchangeably in the literature, although these states are not synonymous. We use arousal to refer to the individual’s current energetic state, whereas activation refers to task-related change in arousal from some baseline.
Methods: SCL, HR, RR, BP, and NS-SCR were simultaneously recorded for each subject during two 3-minute eyes-closed resting periods. The covariation between SCL and other ANS measures was examined between-subjects in baseline 1. Within-subject changes between baselines for these measures were also compared.
Results: Contrary to predictions, SCL was negatively correlated with NS-SCR frequency. Furthermore, SCL and RR were negatively correlated. Consistent with previous findings, no significant positive correlations were found between SCL and BP or HR.
Discussion: These findings suggest that the cardiovascular measures employed are not adequate indices of arousal, but say nothing about activation changes. Further investigation with regard to arousal/activation is warranted.
A MMN gap detection index of left hemisphere advantage for rapid temporal processing in the auditory system
Introduction: Psychophysiological studies have demonstrated a right ear advantage (REA) for detecting brief gaps in broadband sound bursts. However a previous electrophysiological study failed to illustrate a REA in the mismatch negativity (MMN) component of the auditory event-related potential elicited by rare gap stimuli presented amongst repeating narrowband noise bursts. The present study employs broadband noise in an attempt to elicit a REA.
Methods: EEG was recorded from 23 participants presented with monaural broadband noise bursts: 82% standards (continuous 170 ms noise) and three deviant stimuli (6% probability each; 170 ms noise containing 40 ms gaps). Both the temporal position of the gap (1 of 3 levels) and the spectral content of the noise before and after the gap were manipulated to be identical (between channel condition) or non-overlapping (within channel condition).
Results: MMN generated to gap stimuli was larger in within and between channel conditions when the sound sequence was presented to the right ear. The effect was more pronounced for the between channel condition and was dependent on gap position.
Discussion: This study confirmed a REA in MMN elicited by gap stimuli to broadband sounds and that REA is more pronounced when the frequency bands either side of the gap differ.
ANS and CNS estimates of the Orienting Reflex to indifferent and significant stimuli
Introduction: The CNS correlates of the Orienting Reflex (OR) remain unclear. In this exploratory study we used electrodermal measures to define expectations of the OR in the initial trials of an active 50% auditory “oddball” paradigm with a fixed 1.1 s ISI, and sought corresponding effects in the Late Positive Complex (LPC) of the ERP.
Methods: High-pass filtering was used to obtain across-subjects estimates of electrodermal measures of the phasic OR at each stimulus presentation. The LPC was examined as the corresponding CNS estimate of the OR. LORETA was used for source estimation of the LPC at each trial.
Results: SCRs were larger for significant than indifferent stimuli. Both electrodermal response types showed decrement over trials. The LPC to indifferent stimuli was fronto-central (P3a) while that to targets was parietal (P3b). Their sources at trial 1 were substantially different, but both sets showed significant decreases in current density over trials.
Discussion: The separation of the P3a to indifferent vs. P3b to significant stimuli, and their apparent decrement with stimulus repetition, parallels the traditional separation of involuntary and voluntary ORs. This OR perspective may clarify anteriorisation effects in the oddball P3 in clinical samples (e.g. AD/HD) and other paradigms (e.g. Go/NoGo).
Effect of visual distracters on multisensory processing: An event-related potential study
1School of Psychological Science, Latrobe University, Bundoora, Australia
2Brain Sciences Institute, Swinburne University, Hawthorn, Australia
Introduction: As most information processing including multisensory processing occurs in noisy environments, this study investigated how visual distracters affect multisensory integration of letters and novel symbols and sounds.
Methods: Event Related Potentials (ERPs), motor reaction times (MRTs) and accuracy scores were recorded from healthy young females while performing two audiovisual matching tasks (letter and symbol task). Graphemes and phonemes or novel symbols and sounds were presented as unisensory (A and V) or audiovisual (AV) stimuli. Within each task, visual stimuli were also presented individually or in sets of three (one possible match with two distracters).
Results: Motor responses were faster for multisensory matching of symbols compared to letters. Visual distracters increased MRTs and decreased accuracy for both letter and symbol. Early multisensory processes were isolated [AV-(A+V)] at occipitoparietal electrode sites. Visual distracters also increased P1 and N1 amplitude at occipitoparietal electrode sites. N1 amplitude was significantly greater for symbols at right hemisphere parietal electrodes, with minimal differences between letters and symbols at left parietal electrodes.
Discussion: Findings suggest that the right hemisphere is more engaged in the processing of novel information and that neural activity is increased when extracting information and forming multisensory associations amongst distracters.
ERP correlates of categorical word recall in heavy cannabis users
Introduction: In order to better understand and quantify the impacts of regular cannabis use, this study investigated the behavioural and electrophysiological effects of non-acute cannabis intoxication among regular heavy users of cannabis during a delayed verbal serial recall task.
Method: Event-related potentials were recorded from 20 subjects (10 heavy users and 10 non-users of cannabis) matched on verbal IQ and age. Ten lists of 14 discrete words were presented to each subject. Words within each list were of the same category. After a 10-second retention period, participants verbally recalled the words from the list immediately prior. Mean ERP amplitudes were calculated for correctly recalled and non-recalled words for the 300-600 ms and 600-900 ms periods post word presentation.
Results: Cannabis users successfully recalled fewer words than non-users. Significantly greater left and frontal activation was observed for users during both the 300-600 ms and 600-900 ms intervals, and overall activation was greater for users during only the latter.
Discussion: The pattern of brain activity amongst users of cannabis suggests different, and possibly less efficient, processing than controls. Behavioural measures indicate some level of impairment in short-term memory function that may be associated with heavy cannabis use and is evident beyond the period of immediate intoxication.
Cardiovascular response to Stroop: Effect of verbal involvement and task difficulty
Introduction: The effect of verbal involvement and task difficulty on cardiovascular response to the Stroop task was examined.
Methods: Cardiovascular, forearm blood flow (FBF), and epinephrine response of 13 males (20.5 ± 0.4 yr) was assessed during four, five-minute differing versions of the Stroop task. The four versions of the Stroop (order was counterbalanced) included: Stroop 1 (the colour-word conflict task); Stroop 2 (slides in black colour without colour conflict); Stroop 3 (a non-verbal version of Stroop without any oral or behavioural response); and Stroop 4 (the colour-word conflict task with additional conflicting words played on a tape). During Stroop 3 eye gaze was monitored by an experimenter.
Results: Heart rate, FBF, and epinephrine level at Stroop 1 and 4 were higher (P<0.05) compared to Stroop 3, whereas mean arterial pressure at Stroop 1 and 4 were higher than Stroop 2 and 3 (P<0.05). Rating of level of difficulty and concentration was lower for the slides in black colour compared to the other three Stroop tasks.
Discussion: Results suggest that Stroop performance caused significant cardiovascular, FBF, and epinephrine reactivity. This reactivity was attenuated during reading of black coloured words and was virtually abolished when performing the Stroop without verbally responding.
Auditory ERPs in an inter-modal oddball and an inter-modal novelty oddball task
Introduction: To follow up earlier inter-modal oddball research this study investigated ERPs in an inter-modal novelty oddball task (IM Nov) and an inter-modal oddball task (IM O/B). The aim was to investigate the effect of a second (novel) auditory stimulus on ERPs in oddball tasks.
Methods: In both tasks visual standard stimuli were 240 presentations of a pattern-reversal checkerboard. The auditory stimuli were 30 target (2000 Hz, 60 dB) and 30 novel (1000 Hz, 60 dB) tones in the IM Nov and 60 target (2000 Hz, 60 dB) tones in the IM O/B. Auditory stimuli were randomly presented amidst the standards with ISI for all stimuli set at 1.03 s.
Results: ERPs to targets indicated differences between tasks in the later of two prominent frontal N1 components as well as the P250. A comparison of ERPs to target and novel stimuli in the IM Nov showed a negative shift after 200 ms and a late frontal positivity (P350) to novel tones.
Discussion: The results were interpreted as reflecting both early and late processing differences in the novelty oddball condition, due to multiple auditory stimuli. These results are discussed in light of previous auditory and inter-modal research.
ERP indices of varying levels of distraction in an Eriksen flanker task
Introduction: To further current conceptualisations of ERP indices of response competition and interference control, this study investigated the effect of varying the level of distraction created by the flanker stimuli in an Eriksen flanker task.
Methods: Event-related potentials were recorded from 22 subjects during an Eriksen Flanker task in which a central stimulus was flanked by 4 distracting stimuli. As well as the traditional congruent and neutral conditions, there were three incongruent conditions: complete (CI), high (HI) and low (LI). These were created through permutations of the flanking stimuli.
Results: All incongruent conditions produced slower reaction times than the neutral condition, while the congruent condition elicited shorter reaction times than neutral. The CI and HI conditions elicited more errors than neutral trials. N2b amplitudes were increased for CI and HI conditions and P3 amplitudes were reduced for LI and HI conditions relative to the neutral condition. Further, the CI condition elicited longer N2b latencies, and the congruent condition elicited longer N2a latencies when compared with the neutral condition.
Discussion: The findings suggest that there are corresponding and incremental effects on both the late ERP components (N2 and P3) and task performance arising from increased levels of distraction.
Children with Attention-Deficit/Hyperactivity Disorder and autistic features: EEG evidence for comorbid disorders?
Introduction: Attention-Deficit/Hyperactivity Disorder (AD/HD) is the most common psychiatric disorder of childhood, although AD/HD is rarely the only diagnosis given to these children. Within the literature there is some debate as to whether it is valid to diagnose AD/HD as comorbid disorder with autism, as the present diagnostic systems exclude the diagnosis of both of these disorders in the same child. The aim of this study was to determine whether EEG differences exist between two groups of children diagnosed with AD/HD, with one scoring high and one scoring low on a measure of autism.
Methods: The EEG was recorded during an eyes-closed resting condition from 19 electrodes, and Fourier transformed to provide absolute and relative power estimates in delta, theta, alpha and beta bands.
Results: The AD/HD groups both had increased absolute delta and theta, increased relative theta, with deficiencies in relative alpha, compared to a control group. Differences between the two AD/HD groups were primarily found at the frontal midline and central regions.
Discussion: These results suggest the presence of two separate disorders in those individuals with AD/HD and autistic features, and lend support for the diagnosis of AD/HD and autism as comorbid disorders.
The effects of right frontal 1 Hz repetitive transcranial magnetic stimulation on event-related desynchronization of the human EEG: Implications for the treatment of depression
1Alfred Psychiatry Research Centre, Department of Psychological Medicine,
Monash University, Melbourne, Australia
2University of Toronto, Ontario, Canada
3Swinburne University of Technology, Hawthorn, Australia
Introduction: The investigation of repetitive Transcranial Magnetic Stimulation (rTMS) as a potential clinical treatment for major depression is becoming increasingly widespread. However, only a handful of studies have looked at the effect of rTMS on the EEG and results have been heterogeneous. The purpose of the present study is to examine the effects of 1 Hz rTMS applied to dorsal lateral prefrontal cortex on an EEG index of cortical excitation: event-related desynchronization (ERD). It was hypothesized that slow rTMS would lead to a decrease in cortical excitability.
Methods: On two separate occasions, 18 normal participants received 15 minutes of 1 Hz rTMS at 110% of the resting motor threshold. On one occasion this stimulation was to the right DLPFC and on another to the left. EEG was recorded while the participants undertook a version of the stop-signal task both before and after stimulation. ERD was calculated off-line according to methods devised by Pfurtscheller and Aranibar (1977).
Results: Frontally, there was a main effect of rTMS such that theta synchronisation decreased and beta increased following stimulation. Interactions revealed differential effects depending on the laterality of stimulation.
Discussion: Main effects were arguably inline with the hypothesis, but the interactions infer a more complex model.
N1 and P2 components of the auditory event-related potential in younger and older adults
Introduction: In an earlier event-related potential study, we reported amplitude differences in the auditory N1 and P2 components between a younger and older group that could have contributed to the between group difference seen in Mismatch Negativity amplitude.
Methods: We examined the recovery cycle of the N1 and P2 components in younger (mean age = 20.7 years) and older (mean age = 64.8 years) adults by delivering pure tones (800 Hz, 50 ms, 55 dB above threshold) at five different stimulus onset asynchronies (SOAs): 500 ms, 1 s, 3 s, 6 s, and 9 s.
Results: We found a Group x SOA interaction (p<.05) in peak and mean amplitude measures of the N1 component at Cz. The older group tended to show larger N1 amplitude than the young group at the shorter SOAs and smaller amplitude than the young at the longer SOAs. There was also a significant Group x SOA interaction (p<.05) at Cz in peak P2 amplitude with the older group showing reduced amplitude relative to the young especially at the longer SOAs.
Discussion: The study shows that there are age-associated changes in sound processing that are dependent on the interval at which sounds are delivered.
Psychoanatomy of conscious awareness - multistable rivalry of four co-localised motions
1Brain Sciences Institute, Swinburne University of Technology, Hawthorne, Australia
2Latrobe University, Bundoora, Australia
Introduction: We were interested in investigating whether more than two discrete stimuli existing at the one point in space could individually compete for perceptual dominance. This would provide strong confirmation of representational rivalry.
Methods: Experiment 1. Three experienced subjects fused stimuli each containing two coherent motions (Left eye: red-Up/green-Down; right eye: red-Right/green-Left). Dominance durations were measured. Experiment 2. Four coherent motion stimuli were presented (Right: red-Left/green-Down; Left: green-Right/red-Up) viewed with stereo goggles, or all four superimposed and viewed without goggles. Sensitivities to a brief velocity increment/decrement of motion of green dots to the Right when each of the alternate percepts was dominant were assessed using a PEST procedure.
Results: Dominance durations were well-fit by log-normal distributions. 55% of dominance transitions were within eye. Mean suppression ratio was 4.1 when viewing through the stereo goggles and less (2.8) when binocular viewing of the 4 motions was allowed.
Discussion: It appears that the brain deals with 4 overlapping simultaneously competing percepts in a similar way to conventional binocular rivalry, suggesting a salience-driven competition between populations of motion-sensitive neurons. Presenting two motion stimuli to each eye increases the level of suppression without prejudicing eye dominance.
Do GSM mobile phone emissions alter alpha power in humans?
Introduction: Mobile phones (MPs) emit low-level electromagnetic fields that some have argued can affect human neural function. However, demonstrations of such effects have not been consistent. It was the purpose of the present study to test one of the strongest findings in the literature - that of increased ‘alpha’ power in response to MP-type radiation.
Method: Employing a double-blind counterbalanced crossover design, 120 healthy participants received a 30-minute 895 MHz MP exposure condition and a SHAM (visually identical condition but with no emissions), >1 week apart, while electroencephalogram data were recorded. In each condition, alpha power (8-13 Hz) was derived as a function of time, for periods both during and following exposure.
Results: A one-tailed Wilcoxon’s test confirmed previous reports of an overall alpha power enhancement during the MP exposure (relative to SHAM; p=0.013). No change to alpha was observed following exposure cessation (p=0.806; two-tailed). Neither findings were significantly affected by exposure duration.
Discussion: Employing a stronger methodology than previous investigations, the current findings provide strong support for the reported effect of MP exposure on alpha. This effect was relatively small, and it cannot be determined from the present study whether this effect is beneficial or harmful.
Low and high trait impulsiveness in the stop-signal task: Underlying differences in ERPs but not performance
Introduction: The present study examined the relationship between the impulsiveness trait, as measured by Eysenck’s Impulsiveness (IVE) Questionnaire, and stop-signal inhibition in non-clinical adults.
Methods: Extreme low and high impulsivity groups were formed (both groups n = 20) after testing 200 participants with the IVE questionnaire. These selected participants completed a visual/auditory stop task while EEG was recorded. ERPs were computed time-locked to the stop-signal on successful-stop trials, and to the response on failed-stop and no-signal trials. The lateralized readiness potential was time-locked to the go stimulus.
Results: Although the low and high impulsivity groups did not differ on performance measures, ERPs revealed underlying quantitative differences. The LRP was larger in the high than low impulsivity group for stop-signal trials. ERPs for successful stop-trials showed an enhanced N1/P3 complex in the high impulsivity group. Finally, response-locked Pe showed a small tendency towards being larger in the high impulsivity group.
Discussion: Although the impulsiveness trait in the non-clinical population was not associated with overt poor inhibitory control, the findings suggested highly impulsive individuals compensated for an impulsive response style with enhanced stop-signal processing.
An investigation of EEG frequency contribution to ERPs in Attention-Deficit/Hyperactivity Disorder
Introduction: Smaller amplitude ERP components have consistently been found in children with AD/HD compared to controls. The LPC appears as a single waveform, even though it reflects multiple functionally different EEG processes (e.g. P3a, P3b, slow wave). The decomposition of the EEG into specific frequency bands reflecting ERP components may dissociate overlapping components of the LPC and clarify ERP anomalies in AD/HD
Methods: Eighteen AD/HD children were age-matched with 18 controls in this extended study of data from Lawrence et al. (Psychopharmacology, in press). Using a visual CPT paradigm, ERP components to targets were examined within the lower-delta (0 - 2 Hz), upper-delta (2 - 4 Hz), theta (4 - 8 Hz), and alpha (8 - 13 Hz) frequency ranges.
Results: Alpha and theta contributed to the N1, P2, and N2 components; theta and upper-delta contributed to the P3; lower-delta contributed to slow wave activity. Increased frontal and parietal positivity was observed for the AD/HD group in lower-delta.
Discussion: It appears that the main contribution to the LPC is from the delta response. Frontal positivity may be indicative of cognitive dysfunction in the AD/HD group, and its relation with lower-delta may be worth exploring in future studies of task-related activation.
EEG activity in adolescent females with Attention-Deficit/Hyperactivity Disorder
1Brain & Behaviour Research Institute and Department of Psychology, University of Wollongong, Wollongong, Australia
2Sydney Developmental Clinic, Sydney, Australia
Introduction: This study investigated EEG activity in adolescent females with Attention-Deficit/Hyperactivity Disorder (AD/HD).
Methods: Subjects were 15 females with AD/HD and 15 age-matched control subjects, with all subjects aged between 14 and 18 years. The AD/HD group consisted of four subjects with a diagnosis of AD/HD combined subtype and 11 with the inattentive subtype of AD/HD. The EEG was recorded in a single eyes-closed resting condition from 19 electrode sites. Sixty to eighty seconds of raw EEG trace was artifacted and Fourier transformed to obtain absolute and relative power estimates in the delta, alpha, beta and theta bands. Theta/beta and theta/alpha ratios were also calculated.
Results: In comparison to controls, the AD/HD group had reduced absolute beta, increased relative theta, and an increased theta/beta ratio in posterior regions.
Discussion: The results show that female adolescents with AD/HD have abnormal EEGs when compared to controls. These abnormalities may indicate an underlying dysfunction specifically associated with posterior attentional systems and/or the neurotransmitters and structures that serve these regions. This study is the first to separately investigate the EEG of adolescent females with AD/HD.
Is fear processing distinct in males and females? An fMRI study in Posttraumatic Stress Disorder and controls
1Brain Dynamics Centre, Acacia House, Westmead Hospital, Westmead, Australia
2School of Psychology, University of NSW, Sydney, Australia
3Department of Psychology, University of Sydney, Sydney, Australia
4MRI Unit, Dept. of Radiology, Westmead Hospital, Westmead, Australia
5Division of Psychological Medicine, University of Sydney, Sydney, Australia
6Brain Resource Company, Sydney, Australia
Introduction: Females are twice as likely as males to develop Posttraumatic Stress Disorder (PTSD) following trauma, suggesting that a possible biological difference in fear responses may exist in PTSD. Recent fMRI studies in controls suggest females have greater activity in a distributed limbic-brainstem network. This study examines if there is a similar sensitization to fear in PTSD females relative to males, and relative to control populations.
Methods: fMRI activity was examined in response to fearful and neutral faces in 13 female and 10 male PTSD participants, and in 30 female and 30 male non-psychiatric controls (with support from the Brain Resource International Database).
Results: Female controls revealed greater activity to fear faces in ACC, insula and brainstem, and in left amygdala compared to male controls. Similarly, in PTSD, females showed greater activation in brainstem, ACC and insula than males in response to fear. Finally, PTSD females had greater activation in ACC, insula and brainstem than female controls.
Discussion: This study provides evidence of sensitized brainstem-limbic arousal networks in females in response to fear. This sensitization appears particularly enhanced in PTSD females relative to controls. A sensitized arousal system may underlie the greater propensity for women to develop PTSD following trauma.
The influence of target probability on P3: Critical or incidental?
1Brain & Behaviour Research Institute, University of Wollongong, Wollongong, Australia
2Swinburne University of Technology, Hawthorn, Australia
Introduction: The P3 is one of the most widely researched components of the ERP, and context-updating theory which emphasises cognitive factors such as subjective probability, has dominated the P3 landscape for decades. The evidence that P3 amplitude increases with decreases in target probability is unassailable and has been verified in a host of tasks and in all sensory modalities. The P3 link with probability generated the odd-ball paradigm which has become the standard P3 task in both academic and applied settings.
Methods: To determine whether probability independently affects P3, a series of recent studies manipulated target probability and temporal factors in 1- and 2-stimuli tasks, in auditory and visual paradigms, and with varying stimulus intensities.
Results: Converging evidence from a large number of experiments suggests that temporal factors such as the target-to-target interval, and not target probability, underlie the P3 changes previously attributed to target probability, sequence effects and inter stimulus interval.
Discussion: The P3-probability dissociation has major implications for theory concerning P3 amplitude and P3 latency, P3 methodology and P3 applications. This paper summarises published evidence to support the target-to-target interval as an important determinant of P3 amplitude, outlines important implications, and discusses future challenges.
Impact of stability on brain structure
Introduction: The dynamics and stability of networks of brain components is investigated to determine the impact stability plays in constraining the possible network structure of the brain, which is known to lie between a regular network and a random network.
Methods: Using a physiologically based mathematical model of the brain’s electrical activity, the physical dynamics and stability of a network of brain components is calculated. Instabilities in this network model are interpreted to correspond to neurological problems. This implies that stability is a possible constraint on the structure and physiology of a brain network. In this presentation we look at the impact of stability on random networks and make comparisons with the known cortical networks.
Results: For randomly connected networks it will be shown that stability acts as a simple constraint on their structure via a relationship between the number of components in the network, the number of connections, and connection strengths.
Discussion: The results for random networks show that stability constrains brain structure and physiology. Future research into other network types will be outlined, as well as possible applications of stability analysis to neurological problems such as Parkinson’s disease.
Examining the effects of electromagnetic fields emitted by GSM mobile phones on human brain activity and behaviour
1Brain Sciences Institute and 2Bioelectromagnetics Laboratory, Swinburne University of Technology, Hawthorn, Australia
Introduction: Some evidence suggests that exposure to mobile phones (MPs) can affect neural activity, particularly in response to auditory stimuli. We aimed to test recent findings in this area, namely that N100 amplitude and latency would decrease, and that P300 latency and RT would increase, under active relative to sham exposure during an auditory task. Visual measures and accuracy rates were also explored.
Methods: 120 subjects attended two sessions one week apart. In both sessions, participants 1) performed auditory and visual oddball tasks while EEG was recorded with a MP set to sham exposure mounted over the temporal region, and 2) performed the same tasks while the handset was set to active/sham. When active, the MP transmitted for 30 minutes at 895 MHz. Paired t-tests compared difference scores from the sham/sham session to those from the sham/active session.
Results: There was no significant difference between exposure conditions for any auditory or visual ERP component, RT or accuracy. There was also no difference in the perception of transmission or subjective ratings of activation between conditions.
Discussion: As previous positive findings were not replicated, we conclude that there is currently no evidence that acute MP exposure affects these indices of brain activity.
The effect of a multivitamin supplementation on cognition in adults at risk of cognitive decline
Introduction: Deficits in cognitive functioning, especially episodic memory, are commonly reported as people age. It has previously been suggested that cognitive function might be improved with nutritional intervention, and that this may be partly due to a resultant reduction in homocysteine levels. Multivitamins are commonly used supplements in the general population but their effects on cognition are not clear. This study examined the effects of multivitamin supplementation on cognition in adults at risk of cognitive decline.
Methods: Participants were forty males aged 50-69 years. The study was a double blind, placebo controlled design. Participants were randomly allocated to receive either 1 multivitamin or 1 placebo tablet per day. Computerised cognitive tasks and blood homocysteine measures were performed at baseline and after approximately 8 weeks supplementation.
Results: Multivitamin supplementation significantly improved performance on an episodic memory task (p<.01), with no change in the placebo group. Effects of supplementation on other cognitive tasks are discussed. Homocysteine levels were reduced significantly after supplementation with the multivitamin (p<.001) but not with placebo.
Discussion: Eight weeks supplementation with a multivitamin was able to improve performance on an episodic memory task. Multivitamin supplementation may be useful in enhancing cognition in people at risk of cognitive decline.
Acoustic masking by EPI gradient sounds on detection thresholds for amplitude modulation as a function of modulation rate
Introduction: Noise generated during fMRI scanning interferes with the BOLD response and stimulus perception. The temporal nature of scanner noise may alter perception of the temporal properties of sound. This study investigates the extent to which scanner noise impacts upon auditory temporal processing.
Methods: Temporal modulation-transfer functions (TMTFs) were calculated using amplitude-modulation (AM) detection thresholds of white noise carriers for the seven octave modulation rates between 4 and 256 Hz. A 2I-AFC psychophysical procedure was used to estimate thresholds with and without the presence of simultaneous scanner noise. AM thresholds were submitted to a 2 x 7 ANOVA.
Results: TMTFs measured without scanner noise showed the same low pass characteristics established in previous research. However an interaction (p<.01) between AM rate and noise presentation indicated that scanner noise interacts nonlinearly with AM thresholds, with increased masking at slower AM rates and a release from masking observed at faster rates.
Discussion: The results of this study are consistent with modulation masking phenomena, which predict the release from masking seen at AM rates distant from the modulation rate of the scanner noise. These results are discussed in terms of the relevance for auditory fMRI studies using complex AM stimuli such as speech.