ORCID Profile
0000-0002-8483-1068
Current Organisations
Monash University
,
Australian National University
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Publisher: Elsevier BV
Date: 08-2015
DOI: 10.1016/J.PSYCHRES.2015.04.032
Abstract: Working memory impairments in schizophrenia have been strongly associated with abnormalities in gamma oscillations within the dorsolateral prefrontal cortex (DLFPC). We recently published the first ever study showing that anodal transcranial Direct Current Stimulation (tDCS) to the left DLPFC was able to significantly improve working memory performance in schizophrenia. In the current paper we present a secondary analysis from this study, specifically looking at the effect of tDCS on gamma activity and its relationship to working memory. In a repeated measures design we assessed the impact of anodal tDCS (1mA, 2mA, sham) on gamma activity in the left DLPFC at three time-points post-stimulation (0min, 20min, 40min). EEG data was available for 16 participants in the 2mA condition, 13 in the 1mA condition and 12 in the sham condition. Following 2mA stimulation we found a significant increase in gamma event-related synchronisation in the left DLPFC, this was in the context of a significantly improved working memory performance. There was also a significant decrease in gamma event-related synchronisation, with no changes in working memory, following sham stimulation. The current study provides preliminary evidence that tDCS may enhance working memory in schizophrenia by restoring normal gamma oscillatory function.
Publisher: Elsevier BV
Date: 11-2016
DOI: 10.1016/J.PSCYCHRESNS.2016.04.018
Abstract: Huntington's disease (HD) affects GABA-mediated inhibitory circuitry in the cortex. As there is evidence that sex hormones affect GABAergic function, we investigated whether gender modulates GABA-related pathophysiological changes in HD. Fifteen premanifest HD, 11 symptomatic HD and 16 healthy control participants were assessed with paired-pulse transcranial magnetic stimulation applied to the primary motor cortex. Cortical inhibition was significantly reduced in symptomatic HD, compared with premanifest HD and controls. There was reduced inhibition in females overall, but no Group-by-Sex interaction. These findings suggest that sex hormones do not exert a direct influence on the mechanisms underpinning cortical inhibitory deficits in HD.
Publisher: Elsevier BV
Date: 2016
Publisher: Cold Spring Harbor Laboratory
Date: 04-10-2022
DOI: 10.1101/2022.10.03.510571
Abstract: Obsessive-Compulsive Disorder (OCD) is a mental health condition causing significant decline in the quality of life of sufferers and the limited knowledge on the pathophysiology hinders successful treatment. The aim of the current study was to examine electroencephalographic (EEG) findings of OCD to broaden our understanding of the disease. Resting-state eyes-closed EEG data was recorded from 25 in iduals with OCD and 27 healthy controls (HC). The 1/f arrhythmic activity was removed prior to computing oscillatory powers of all frequency bands (delta, theta, alpha, beta, gamma). Cluster-based permutation was used for between-group statistical analyses, and comparisons were performed for the 1/f slope and intercept parameters. Functional connectivity (FC) was measured using coherence and debiased weighted phase lag index (d-wPLI), and statistically analysed using the Network Based Statistic method. Compared to HC, the OCD group showed increased oscillatory power in the delta and theta bands in the fronto-temporal and parietal brain regions. However, there were no significant between-group findings in other bands or 1/f parameters. The coherence measure showed significantly reduced FC in the delta band in OCD compared to HC but the d-wPLI analysis showed no significant differences. OCD is associated with raised oscillatory power in slow frequency bands in the fronto-temporal brain regions, which agrees with the previous literature and therefore is a potential biomarker. Although delta coherence was found to be lower in OCD, due to inconsistencies found between measures and the previous literature, further research is required to ascertain definitive conclusions.
Publisher: Elsevier BV
Date: 06-2022
DOI: 10.1016/J.BPSC.2021.10.017
Abstract: Brain connectivity can be estimated through many analyses applied to electroencephalography (EEG) data. However, substantial heterogeneity in the implementation of connectivity methods exists. Heterogeneity in conceptualization of connectivity measures, data collection, or data preprocessing may be associated with variability in robustness of measurement. While it is difficult to compare the results of studies using different EEG connectivity measures, standardization of processing and reporting may facilitate the task. We discuss how factors such as referencing, epoch length and number, controls for volume conduction, artifact removal, and statistical control of multiple comparisons influence the EEG connectivity estimate for connectivity measures, and what can be done to control for potential confounds associated with these factors. Based on the results reported in previous literature, this article presents recommendations and a novel checklist developed for quality assessment of EEG connectivity studies. This checklist and its recommendations are made in an effort to draw attention to factors that may influence connectivity estimates and factors that need to be improved in future research. Standardization of procedures and reporting in EEG connectivity may lead to EEG connectivity studies being made more synthesizable and comparable despite variations in the methodology underlying connectivity estimates.
Publisher: Elsevier BV
Date: 05-2023
Publisher: Springer Science and Business Media LLC
Date: 08-02-2019
Publisher: Elsevier BV
Date: 05-2023
Publisher: Hindawi Limited
Date: 31-08-2023
DOI: 10.1155/2023/9958884
Publisher: Elsevier BV
Date: 03-2015
Publisher: Elsevier BV
Date: 05-2016
DOI: 10.1016/J.NEULET.2016.03.038
Abstract: Striatal degeneration in Huntington's disease (HD) causes changes in cortico-subcortical pathways. Transcranial magnetic stimulation (TMS) is a valuable tool for assessing pathophysiology within these pathways, yet has had limited application in HD. As cortico-subcortical pathways are largely mediated by GABA and dopamine receptor genes, understanding how these genes modulate neurophysiology in HD may provide new insights into how underlying pathology maps onto clinical phenotype. Twenty-nine participants with HD underwent motor cortex stimulation, while corticospinal excitability, cortical inhibition and intracortical facilitation were indexed via peripheral electromyography. Single-nucleotide polymorphism mapping was performed across six genes that are known to modulate cortico-subcortical pathways (GABRA2, GABBR1, GABBR2, DRD1, DRD2, DRD4). Genetic associations with six TMS measures and age at onset were investigated. Our hierarchical multiple regression analysis, controlling for CAG and age, revealed that a GABBR2 variant, predicted to be disease-causative, was significantly associated with corticospinal excitability at corrected levels. A subsequent uncorrected exploratory analysis revealed associations between GABBR2, GABRA2 and DRD2 variants with TMS measures of corticospinal excitability and cortical inhibition in HD, as well as with age at onset. Our findings support the notion that uncovering genetic associations with pathophysiological measures and age at onset is an important way forward in terms of generating meaningful biomarkers with diagnostic and prognostic sensitivity, and identifying novel human-validated targets for future clinical trials.
Publisher: Informa UK Limited
Date: 17-01-2017
DOI: 10.1080/02699052.2016.1239273
Abstract: Alterations to functional connectivity following a traumatic brain injury (TBI) may lead to impaired cognitive performance and major depressive disorder (MDD). In particular, functional gamma band connectivity is thought to reflect information binding important for working memory. The objective of this study was to determine whether altered functional gamma connectivity may be a factor in MDD following TBI (TBI-MDD). This study assessed in iduals with TBI-MDD, as well as in iduals with TBI alone and MDD alone using electroencephalographic recordings while participants performed a working memory task to assess differences in functional connectivity between these groups. Functional connectivity was compared using the debiased weighted phase lag index (wPLI). wPLI was measured from a group of healthy controls (n = 31), participants with MDD (n = 17), participants with TBI (n = 20) and participants with TBI-MDD (n = 15). Contrary to the predictions, this study found both the groups with TBI and TBI-MDD showed higher gamma connectivity from posterior regions during WM retention. This may reflect dysfunctional functional connectivity in these groups, as a result of maladaptive neuroplastic reorganization.
Publisher: Springer Science and Business Media LLC
Date: 05-10-2023
Publisher: Cold Spring Harbor Laboratory
Date: 05-11-2022
DOI: 10.1101/2022.11.05.515279
Abstract: Obsessive-Compulsive Disorder (OCD) is a psychiatric condition leading to significant distress and poor quality of life. Successful treatment of OCD is restricted by the limited knowledge about its pathophysiology. This study aimed to investigate the pathophysiology of OCD using electroencephalographic (EEG) event related potentials (ERP), elicited from multiple tasks to characterise disorder-related differences in underlying brain activity across multiple neural processes. ERP data were obtained from 25 OCD patients and 27 age- and sex-matched healthy controls (HC) by recording EEG during Flanker and Go/Nogo tasks. Error-related negativity (ERN) was elicited by the Flanker task, while N200 and P300 were generated using the Go/Nogo task. Primary comparisons of the neural response litudes and the topographical distribution of neural activity were conducted using scalp field differences across all time points and electrodes. Compared to HC, the OCD group showed altered ERP distributions. Contrasting with the previous literature on ERN and N200 topographies in OCD where fronto-central negative voltages were reported, we detected positive voltages. Additionally, the P300 was found to be less negative in the frontal regions. None of these ERP findings were associated with OCD symptom severity. These results indicate that in iduals with OCD show altered frontal neural activity across multiple executive function related processes, supporting the frontal dysfunction theory of OCD. Furthermore, due to the lack of association between altered ERPs and OCD symptom severity, they may be considered potential candidate endophenotypes for OCD.
Publisher: Elsevier BV
Date: 11-2015
DOI: 10.1016/J.CONCOG.2015.07.002
Abstract: Meditation and spiritual practices are conceptually similar, eliciting similar subjective experiences, and both appear to provide similar benefits to the practicing in iduals. However, no research has examined whether the mechanism of action leading to the beneficial effects is similar in both practices. This review examines the neuroimaging research that has focused on groups of meditating in iduals, groups who engage in religious/spiritual practices, and research that has examined groups who perform both practices together, in an attempt to assess whether this may be the case. Differences in the balance of activity between the parietal and prefrontal cortical activation were found between the three groups. A relative prefrontal increase was reflective of mindfulness, which related to decreased anxiety and improved well-being. A relative decrease in activation of the parietal cortex, specifically the inferior parietal cortex, appears to be reflective of spiritual belief, whether within the context of meditation or not. Because mindful and spiritual practices differ in focus regarding the 'self' or 'other' (higher being), these observations about neurological components that reflect spirituality may continue work towards understanding how the definition of 'self' and 'other' is represented in the brain, and how this may be reflected in behaviour. Future research can begin to use cohorts of participants in mindfulness studies which are controlled for using the variable of spirituality to explicitly examine how functional and structural similarities and differences may arise.
Publisher: Springer Science and Business Media LLC
Date: 26-04-2016
DOI: 10.1007/S00702-016-1554-1
Abstract: Working memory impairment in schizophrenia has been strongly associated with abnormalities in gamma oscillations within the dorsolateral prefrontal cortex (DLFPC). We recently published the first ever study showing that anodal transcranial direct current stimulation (tDCS) to the left DLPFC was able to significantly improve working memory in schizophrenia and did so seemingly via restoring normal gamma oscillatory function. Transcranial alternating current stimulation (tACS) is a form of electrical brain stimulation that delivers stimulation at a specific frequency and has been shown to entrain endogenous cortical oscillations. Therefore, gamma (γ) tACS may be even more effective than tDCS in improving working memory in schizophrenia. In a randomized repeated-measures study we compared the effects of γ-tACS, tDCS and sham stimulation on the performance of the two back working memory tasks in ten patients with schizophrenia. There was a significant time by stimulation interaction, with tDCS and sham showing trend-level improvements in working memory, while γ-tACS, contrary to our hypothesis, showed no change. The results are discussed in light of posited ergent effects of tACS and tDCS on the pathophysiology of working memory impairment in schizophrenia.
Publisher: Elsevier BV
Date: 03-2019
DOI: 10.1016/J.JANXDIS.2018.11.001
Abstract: Obsessive-compulsive disorder (OCD) is a chronic disease that causes significant decline in the quality of life of those affected. Due to our limited understanding of the underlying pathophysiology of OCD, successful treatment remains elusive. Although many have studied the pathophysiology of OCD through electroencephalography (EEG), limited attempts have been made to synthesize and interpret their findings. To bridge this gap, we conducted a comprehensive literature review using Medline/PubMed and considered the 65 most relevant studies published before June 2018. The findings are categorised into quantitative EEG, sleep related EEG and event related potentials (ERPs). Increased frontal asymmetry, frontal slowing and an enhancement in the ERP known as error related negativity (ERN) were consistent findings in OCD. However, sleep EEG and other ERP (P3 and N2) findings were inconsistent. Additionally, we analysed the usefulness of ERN as a potential candidate endophenotype. We hypothesize that dysfunctional frontal circuitry and overactive performance monitoring are the major underlying impairments in OCD. Additionally, we conceptualized that defective fronto-striato-thalamic circuitry causing poor cerebral functional connectivity gives rise to the OCD behavioural manifestations. Finally, we have discussed transcranial magnetic stimulation and EEG (TMS-EEG) applications in future research to further our knowledge of the underlying pathophysiology of OCD.
Publisher: Wiley
Date: 24-09-2012
DOI: 10.1002/HBM.22171
Publisher: Cold Spring Harbor Laboratory
Date: 20-08-2018
DOI: 10.1101/396259
Abstract: Attention is a vital executive function, since other executive functions are largely dependent on it. Mindfulness meditation has been shown to enhance attention. However, the components of attention altered by meditation and the related neural activities are underexplored. In particular, the contributions of inhibitory processes and sustained attention are not well understood. Additionally, it is not clear whether improvements in attention are related to increases in the strength of typically activated brain areas, or the recruitment of additional or alternative brain areas. To address these points, 34 meditators were compared to 28 age and gender matched controls during electroencephalography (EEG) recordings of neural activity during a Go/Nogo response inhibition task. This task generates a P3 event related potential, which is related to response inhibition processes in Nogo trials, and attention processes across both trial types. Compared with controls, meditators were more accurate at responding to Go and Nogo trials. Meditators showed a more frontally distributed P3 to both Go and Nogo trials, suggesting more frontal involvement in sustained attention rather than activity specific to response inhibition. Unexpectedly, meditators also showed increased positivity over the right parietal cortex prior to visual information reaching the occipital cortex. Both results were positively related to increased accuracy across both groups. The results suggest that meditators have an increased capacity to modulate a range of neural processes in order to meet task requirements, including higher order processes, and sensory anticipation processes. This increased capacity may underlie the improved attentional function observed in mindfulness meditators.
Publisher: Elsevier BV
Date: 05-2014
DOI: 10.1016/J.BIOPSYCHO.2014.03.008
Abstract: Rates of major depressive disorder (MDD) following traumatic brain injury (TBI) are higher than in the general population. In iduals with depression following traumatic brain injury (TBI-MDD) exhibit working memory (WM) impairments. Electrophysiological evidence has suggested that parieto-occipital upper alpha synchronisation may enhance WM retention by inhibiting irrelevant processes. The current research assessed whether retention period WM parieto-occipital upper alpha activity is disrupted in groups with TBI-only (N=20), MDD (N=17), and TBI-MDD (N=15) compared to healthy controls (N=31). Behavioural data indicated poorer performance in MDD and TBI-MDD. Parietal-occipital upper alpha was reduced in the MDD and TBI-MDD groups, but was unaffected in TBI-only. These results suggest inhibitory deficits may account for WM impairments in MDD and TBI-MDD, and that for in iduals with TBI-MDD it may be the depression rather than the TBI that impairs WM.
Publisher: Oxford University Press (OUP)
Date: 23-09-2015
Abstract: Noninvasive brain stimulation is increasingly being investigated for the enhancement of cognition, yet current approaches appear to be limited in their degree and duration of effects. The majority of studies to date have delivered stimulation in "standard" ways (i.e., anodal transcranial direct current stimulation or high-frequency transcranial magnetic stimulation). Specialized forms of stimulation, such as theta burst stimulation (TBS), which more closely mimic the brains natural firing patterns may have greater effects on cognitive performance. We report here the findings from the first-ever investigation into the persistent cognitive and electrophysiological effects of intermittent TBS (iTBS) delivered to the left dorsolateral prefrontal cortex. In 19 healthy controls, active iTBS significantly improved performance on an assessment of working memory when compared with sham stimulation across a period of 40 min post stimulation. The behavioral findings were accompanied by increases in task-related fronto-parietal theta sychronization and parietal gamma band power. These results have implications for the role of more specialized stimulation approaches in neuromodulation.
Publisher: Informa UK Limited
Date: 28-03-2016
DOI: 10.1080/17470919.2016.1166154
Abstract: The dorsolateral prefrontal cortex (DLPFC) is thought to play a key role in the cognitive control of emotion and has therefore, unsurprisingly, been implicated in the regulation of physical pain perception. This brain region may also influence the experience of social pain, which has been shown to activate similar neural networks as seen in response to physical pain. Here, we applied sham or active low-frequency (1 Hz) repetitive transcranial magnetic stimulation (rTMS) to the left DLPFC, previously shown to exert bilateral effects in pain perception, in healthy participants. Following stimulation, participants played the "Cyberball Task" an online ball-tossing game in which the subject participant is included or excluded. Compared to sham, rTMS did not modulate behavioural response to social exclusion. However, within the active rTMS group only, greater trait personal distress was related to enhanced negative outcomes to social exclusion. These results add further support to the notion that the effect of brain stimulation is not homogenous across in iduals, and indicates the need to consider baseline in idual differences when assessing response to brain stimulation. This seems particularly relevant in social neuroscience investigations, where trait factors may have a meaningful effect.
Publisher: Elsevier BV
Date: 2016
DOI: 10.1016/J.BBR.2015.09.030
Abstract: Although progress has been made towards understanding the gross cortical and subcortical pathology of Huntington's disease (HD), there remains little understanding of the progressive pathophysiological changes that occur in the brain circuits underlying the disease. Transcranial magnetic stimulation (TMS) enables investigation of the functional integrity of cortico-subcortical pathways, yet it has not been widely applied in HD research to date. This study sought to characterise profiles of cortical excitability, including inhibition and facilitation, in groups of premanifest and symptomatic HD participants via the use of TMS. We also investigated the clinical, neurocognitive and psychiatric correlates of cortical excitability to better understand the development of phenotypic heterogeneity. The s le comprised 16 premanifest HD, 12 early symptomatic HD and 17 healthy control participants. Single- and paired-pulse TMS protocols were administered to the left primary motor cortex, with surface electromyography recorded from the abductor pollicis brevis muscle. Short-interval cortical inhibition was significantly reduced in symptomatic HD, compared with premanifest HD and controls, and was significantly correlated with pathological burden and neurocognitive performance. There was also reduced long-interval cortical inhibition in both premanifest and symptomatic HD, compared with controls, which was associated with pathological burden and psychiatric disturbances. Motor thresholds, cortical silent periods and intracortical facilitation did not differ across groups. Our results provide important new insights into pathophysiological changes in cortico-subcortical circuits across disease stages in HD. We propose that neurophysiological measures obtained via TMS have potential utility as endophenotypic biomarkers in HD, given their association with both pathological burden and clinical phenotype.
Publisher: Elsevier BV
Date: 10-2021
Publisher: Elsevier BV
Date: 2019
DOI: 10.1016/J.JAD.2018.08.058
Abstract: Non-response to repetitive transcranial magnetic stimulation (rTMS) treatment for depression is costly for both patients and clinics. Simple and cheap methods to predict response would reduce this burden. Resting EEG measures differentiate responders from non-responders, so may have utility for response prediction. Fifty patients with treatment resistant depression and 21 controls had resting electroencephalography (EEG) recorded at baseline (BL). Patients underwent 5-8 weeks of rTMS treatment, with EEG recordings repeated at week 1 (W1). Forty-two participants had valid BL and W1 EEG data, and 12 were responders. Responders and non-responders were compared at BL and W1 in measures of theta (4-8 Hz) and alpha (8-13 Hz) power and connectivity, frontal theta cordance and alpha peak frequency. Control group comparisons were made for measures that differed between responders and non-responders. A machine learning algorithm assessed the potential to differentiate responders from non-responders using EEG measures in combination with change in depression scores from BL to W1. Responders showed elevated theta connectivity across BL and W1. No other EEG measures differed between groups. Responders could be distinguished from non-responders with a mean sensitivity of 0.84 (p = 0.001) and specificity of 0.89 (p = 0.002) using cross-validated machine learning classification on the combination of all EEG and mood measures. The low response rate limited our s le size to only 12 responders. Resting theta connectivity at BL and W1 differ between responders and non-responders, and show potential for predicting response to rTMS treatment for depression.
Publisher: Elsevier BV
Date: 03-2015
DOI: 10.1016/J.BIOPSYCHO.2015.01.011
Abstract: Impaired error awareness is related to poorer outcome following traumatic brain injury (TBI). Error awareness deficits are also found in major depressive disorder (MDD), but have not been examined in the MDD that follows a TBI (TBI-MDD). This study assessed neural activity related to error awareness in TBI-MDD. Four groups completed a response inhibition task while EEG was recorded- healthy controls (N = 15), MDD-only (N = 15), TBI-only (N = 16), and TBI-MDD (N = 12). Error related EEG activity was compared using powerful randomisation statistics that included all electrodes and time points. Participants with TBI-MDD displayed less frontally distributed neural activity, suggesting reduced contribution from frontal generating sources. Neural activity during this time window is thought to reflect conscious awareness of errors. The TBI-only and MDD-only groups did not differ from controls, and early error processing was unaffected, suggesting early error detection is intact.
Publisher: Elsevier BV
Date: 12-2016
DOI: 10.1016/J.ULTRASMEDBIO.2016.08.003
Abstract: Ultrasound (US) at diagnostic frequency and power is known to alter nerve potentials however, the precise mechanism of action is unknown. We investigated whether US alters resting nerve potential to lower the threshold for magnetic nerve stimulation. Seventeen healthy subjects were recruited. For each subject, a 1.5 MHz US imaging probe was placed onto the elbow with the beam directed at the ulnar nerve. The probe was coupled to the skin using standard acoustic coupling gel as would be done for a routine clinical US scan. Ulnar nerve stimulation was performed simultaneously with magnetic stimulation (MS). Successful magnetic stimulation of the ulnar nerve was confirmed with nerve potentials measured by electromyography. There was no significant change in electromyography signal when MS was performed during US exposure. US at the diagnostic frequency and power tested does not alter nerve thresholds with MS. Testing at other frequencies is required, however, before US is negated as a technique to modify MS thresholds.
Publisher: Springer Science and Business Media LLC
Date: 10-04-2018
Publisher: Elsevier BV
Date: 07-2017
DOI: 10.1016/J.CLINPH.2017.04.005
Abstract: To examine the effects of intermittent TBS (iTBS) and continuous TBS (cTBS) on cortical reactivity in the dorsolateral prefrontal cortex. 10 healthy participants were stimulated with either iTBS, cTBS or sham at F3 electrode. Single- and paired-pulse TMS and concurrent electroencephalography (EEG) were used to assess change in cortical reactivity and long-interval intracortical inhibition (LICI) via TMS-evoked potentials (TEPs) and TMS-evoked oscillations. Significant increases in N120 litudes (p<0.01) were observed following iTBS over prefrontal cortex. Changes in TMS-evoked theta oscillations and LICI of theta oscillations were also observed following iTBS (increase) and cTBS (decrease). Change in LICI of theta oscillations correlated with change in N120 litude following TBS (r=-0.670, p=0.001). This study provides preliminary evidence that TBS produces direct changes in cortical reactivity in the prefrontal cortex. Combining TBS with TMS-EEG may be a useful approach to optimise stimulation paradigms prior to the conduct of clinical trials. TBS is able to modulate cortical reactivity and cortical inhibition in the prefrontal cortex.
Publisher: Springer Science and Business Media LLC
Date: 2023
DOI: 10.1007/S12671-022-02052-W
Abstract: Mindfulness meditation is associated with better attention function. Performance monitoring and error-processing are important aspects of attention. We investigated whether experienced meditators showed different neural activity related to performance monitoring and error-processing. Previous research has produced inconsistent results. This study used more rigorous analyses and a larger s le to resolve the inconsistencies. We used electroencephalography (EEG) to measure the error-related negativity (ERN) and error positivity (Pe) following correct and incorrect responses to a Go/Nogo task from 27 experienced meditators and 27 non-meditators. No differences were found in the ERN (all p 0.05). Meditators showed larger global field potentials (GFP) in the Pe after correct responses and errors, indicating stronger neural responses ( p = 0.019, FDR-p = 0.152, np 2 = 0.095, BFincl = 2.691). This effect did not pass multiple comparison controls. However, single-electrode analysis of the Pe did pass multiple comparison controls ( p = 0.002, FDR-p = 0.016, np 2 = 0.133, BFincl = 220.659). Meditators also showed a significantly larger Pe GFP for errors, which would have passed multiple comparison controls, but was not a primary analysis ( p = 0.003, np 2 = 0.149, BF10 = 9.999). Meditation may strengthen neural responses related to performance monitoring. However, these strengthened neural responses were not specific to error monitoring (although the error-related Pe may be more sensitive to group differences than the correct response Pe). These conclusions remain tentative, because the single-electrode analysis passed multiple comparison controls, but the analysis including all electrodes did not. This study was not preregistered.
Publisher: Elsevier BV
Date: 12-2014
DOI: 10.1016/J.PSCYCHRESNS.2014.09.008
Abstract: Rates of major depressive disorder (MDD) following traumatic brain injury (TBI) are estimated to be between 20% and 45%, a higher prevalence than that seen in the general population. These increased rates may be due to specific changes in brain function following TBI. Event related potentials (ERPs) are well suited for measuring the electrophysiological differences between groups in areas of cognitive processing impaired in both MDD and TBI, such as response inhibition. The current study presented an emotional Go/Nogo task (with schematic emotional faces as stimuli) to participants with TBI, participants with MDD, and participants with both TBI and MDD (TBI-MDD). Topographical distribution of activity and global field power comparisons were made across stimulus-locked epochs between these groups and healthy controls. The results indicated that ERPs were not altered by TBI alone. Both MDD and TBI-MDD groups showed similar alterations in topographical distribution and global field power in the N2 window, as well as late epoch alterations. The MDD and TBI-MDD groups showed significantly less fronto-central negativity during the N2 window in Nogo trials compared with the control group. The MDD and TBI-MDD groups also showed significantly less global field power in Nogo trials than Go trials during the N2 window while the control group showed the opposite pattern. The MDD and TBI-MDD groups showed no mood-congruent bias in behavioural or ERP measures. The results suggest that TBI-MDD displays similar electrophysiological changes to those found in the MDD group without TBI.
Publisher: Elsevier BV
Date: 11-2013
DOI: 10.1016/J.BRS.2013.04.006
Abstract: High and low frequency repetitive transcranial magnetic stimulation (rTMS) are both used to treat major depressive disorder(MDD). However, the physiological mechanisms underlying the therapeutic benefit and the effect of the stimulation frequency are unclear. Twelve healthy participants received 1Hz, 2Hz, and 5Hz active rTMS. Twenty 5 second trains were delivered at left dorsolateral prefrontal cortex at 110% of resting motor threshold with a 25 second inter-train interval. Blood oxygenation (HbO) was significantly reduced following the 1Hz trains compared to the HbO increases observed in both the 2Hz and 5Hz conditions. There was no significant inter-hemispheric difference in response. These results suggest that short trains of high and low frequency rTMS delivered to prefrontal cortex evoke a differential HbO response and provide additional evidence that high frequency trains result in increased neural activity. The findings may provide further explanation for the improved symptoms observed in MDD patients treated with high frequency rTMS.
Publisher: Elsevier BV
Date: 11-2014
DOI: 10.1016/J.NEUROIMAGE.2014.07.037
Abstract: The combination of transcranial magnetic stimulation and electroencephalography (TMS-EEG) is emerging as a powerful tool for causally investigating cortical mechanisms and networks. However, various artefacts contaminate TMS-EEG recordings, particularly over regions such as the dorsolateral prefrontal cortex (DLPFC). The aim of this study was to substantiate removal of artefacts from TMS-EEG recordings following stimulation of the DLPFC and motor cortex using independent component analysis (ICA). 36 healthy volunteers (30.8 ± 9 years, 9 female) received 75 single TMS pulses to the left DLPFC or left motor cortex while EEG was recorded from 57 electrodes. A subset of 9 volunteers also received 50 sham pulses. The large TMS artefact and early muscle activity (-2 to ~15 ms) were removed using interpolation and the remaining EEG signal was processed in two separate ICA runs using the FastICA algorithm. Five sub-types of TMS-related artefacts were manually identified: remaining muscle artefacts, decay artefacts, blink artefacts, auditory-evoked potentials and other noise-related artefacts. The cause of proposed blink and auditory-evoked potentials was assessed by concatenating known artefacts (i.e. voluntary blinks or auditory-evoked potentials resulting from sham TMS) to the TMS trials before ICA and evaluating grouping of resultant independent components (ICs). Finally, we assessed the effect of removing specific artefact types on TMS-evoked potentials (TEPs) and TMS-evoked oscillations. Over DLPFC, ICs from proposed muscle and decay artefacts correlated with TMS-evoked muscle activity size, whereas proposed TMS-evoked blink ICs combined with voluntary blinks and auditory ICs with auditory-evoked potentials from sham TMS. In idual artefact sub-types characteristically distorted each measure of DLPFC function across the scalp. When free of artefact, TEPs and TMS-evoked oscillations could be measured following DLPFC stimulation. Importantly, characteristic TEPs following motor cortex stimulation (N15, P30, N45, P60, N100) could be recovered from artefactual data, corroborating the reliability of ICA-based artefact correction. Various different artefacts contaminate TMS-EEG recordings over the DLPFC and motor cortex. However, these artefacts can be removed with apparent minimal impact on neural activity using ICA, allowing the study of TMS-evoked cortical network properties.
Publisher: Public Library of Science (PLoS)
Date: 06-08-2019
Publisher: Elsevier BV
Date: 09-2014
DOI: 10.1016/J.BBR.2014.05.047
Abstract: Previous research suggests that many people who sustain a traumatic brain injury (TBI), even of the mild form, will develop major depression (MD). We previously reported white matter integrity differences between those who did and did not develop MD after mild TBI. In this current paper, we aimed to investigate whether there were also volumetric differences between these groups, as suggested by previous volumetric studies in mild TBI populations. A s le of TBI-with-MD subjects (N=14), TBI-without-MD subjects (N=12), MD-without-TBI (N=26) and control subjects (no TBI or MD, N=23), received structural MRI brain scans. T1-weighted data were analysed using the Freesurfer software package which produces automated volumetric results. The findings of this study indicate that (1) TBI patients who develop MD have reduced volume in temporal, parietal and lingual regions compared to TBI patients who do not develop MD, and (2) MD patients with a history of TBI have decreased volume in the temporal region compared to those who had MD but without a history of TBI. We also found that more severe MD in those with TBI-with-MD significantly correlated with reduced volume in anterior cingulate, temporal lobe and insula. These findings suggest that volumetric reduction to specific regions, including parietal, temporal and occipital lobes, after a mild TBI may underlie the susceptibility of these patients developing major depression, in addition to altered white matter integrity.
Publisher: Springer Science and Business Media LLC
Date: 07-2023
DOI: 10.1007/S12671-023-02168-7
Abstract: Online mindfulness programs have become popular due to their increased accessibility compared to face-to-face programs. Although research has demonstrated that face-to-face mindfulness programs can increase trait mindfulness, self-compassion, and prosocial attitudes, fewer studies have explored these outcomes in online programs. This study aimed to test whether an online mindfulness program improved trait mindfulness, self-compassion, and prosocial attitudes, and whether improvements related to self-reported quality and quantity of mindfulness practice. Repeated-measures ANOVAs compared measures of trait mindfulness, self-compassion, and prosocial attitudes between 209 pre- and post-program survey responses from participants who completed a 4-week online mindfulness program. Regressions were used to test whether the quantity or quality of mindfulness practice predicted changes in these measures, and mediation analyses tested whether associations between mindfulness practice and outcomes were mediated by changes in trait mindfulness. The study found that participation in the mindfulness program was associated with improved trait mindfulness, self-compassion, and prosocial attitudes (all p 0.01) and that males showed larger increases in prosocial attitudes ( p 0.05). The study also showed an association between the quality of formal mindfulness practice and improvements in both self-compassion and trait mindfulness ( p 0.01). Lastly, the mediation analysis suggested the association between the quality of formal practice and self-compassion was mediated by changes in trait mindfulness ( p 0.05). These results suggest online mindfulness programs can lead to improved trait mindfulness, self-compassion, and prosocial attitudes. Our results also indicate that higher self-reported practice quality is related to improved trait mindfulness, and that changes in trait mindfulness mediated improved self-compassion. This study was not pre-registered.
Publisher: Elsevier BV
Date: 05-2023
Publisher: Elsevier BV
Date: 2018
DOI: 10.1016/J.BRS.2017.10.015
Abstract: Repetitive transcranial magnetic stimulation (rTMS) is an effective treatment for depression, but only some in iduals respond. Predicting response could reduce patient and clinical burden. Neural activity related to working memory (WM) has been related to mood improvements, so may represent a biomarker for response prediction. We expected higher theta and alpha activity in responders compared to non-responders to rTMS. Fifty patients with treatment resistant depression and twenty controls performed a WM task while electroencephalography (EEG) was recorded. Patients underwent 5-8 weeks of rTMS treatment, repeating the EEG at week 1 (W1). Of the 39 participants with valid WM-related EEG data from baseline and W1, 10 were responders. Comparisons between responders and non-responders were made at baseline and W1 for measures of theta (4-8 Hz), upper alpha (10-12.5 Hz), and gamma (30-45 Hz) power, connectivity, and theta-gamma coupling. The control group's measures were compared to the depression group's baseline measures separately. Responders showed higher levels of WM-related fronto-midline theta power and theta connectivity compared to non-responders at baseline and W1. Responder's fronto-midline theta power and connectivity was similar to controls. Responders also showed an increase in gamma connectivity from baseline to W1, with a concurrent improvement in mood and WM reaction times. An unbiased combination of all measures provided mean sensitivity of 0.90 at predicting responders and specificity of 0.92 in a predictive machine learning algorithm. Baseline and W1 fronto-midline theta power and theta connectivity show good potential for predicting response to rTMS treatment for depression.
Publisher: Elsevier BV
Date: 07-2013
DOI: 10.1016/J.BRS.2012.12.001
Abstract: Prefrontal transcranial magnetic stimulation (TMS) is being investigated as a treatment for several neurological and psychiatric disorders. The direction of the cortical current induced by TMS can be modulated by the coil orientation and this influences the extent of neural depolarization. Although the optimal coil orientation has previously been established for motor cortex, identifying an optimal coil orientation for prefrontal areas is more challenging due to the absence of a motor response. The current study used near infra-red spectroscopy (NIRS) to investigate the impact of coil orientation on TMS induced changes in prefrontal blood oxygenation (HbO). It was hypothesized that a greater change in HbO would be observed when current was induced in a posterior to anterior direction. Single pulse and trains of 1 Hz repetitive TMS (rTMS) were administered to the left prefrontal cortex while simultaneously recording HbO response bilaterally. The effect of coil orientation was examined at 45°, 135°, and 225° counterclockwise from midline. Greatest changes in HbO were observed at a 45° orientation when both single and rTMS were applied, and only minor changes were observed at 135° and 225°. Application of short trains of rTMS at 45° resulted in transient increases in HbO that were significantly greater in magnitude than when the coil orientation was reversed. The utility of NIRS for examining the TMS evoked physiological response at non-motor areas is highlighted in this study. Prefrontal HbO response evoked by TMS is sensitive to the direction of induced cortical current and it appears that the de facto 45° angle utilized in most clinical studies may prove to be optimal.
Publisher: Elsevier BV
Date: 12-2015
DOI: 10.1016/J.BANDC.2015.11.002
Abstract: Transcranial Direct Current Stimulation (tDCS) has been widely investigated for its potential to enhance cognition, and in particular working memory, however to date standard approaches to stimulation have shown only modest effects. Alternative, more specialised, forms of current delivery may be better suited to cognitive enhancement. One such method is transcranial Alternating Current Stimulation (tACS) which delivers stimulation at a specific frequency and has been shown to entrain endogenous cortical oscillations which underlie cognitive functioning. To date there has been no comparison of the effects of tACS to those of tDCS on cognitive enhancement. In a randomised repeated-measures study design we assessed the effect of gamma (γ)-tACS, tDCS and sham tDCS on working memory in 18 healthy participants who attended three sessions held at least 72h apart. Pre- and post-stimulation working memory performance was assessed using the 2 and 3-back. Our findings indicated the presence of a selective improvement in performance on the 3-back task following γ-tACS compared with tDCS and sham stimulation. The current findings provide support for further and more detailed investigation of the role of γ-tACS as a more specialised approach to neuromodulation.
No related grants have been discovered for Neil Bailey.