[show abstract][hide abstract] ABSTRACT: This study sought to explore whether the so-called 'paradoxical' task-related increases in the alpha bandwidth of the human electroencephalogram result from increases in evoked (phase locked), as opposed to induced (non-phase locked), activity. The electroencephalograms of 18 participants were recorded while they engaged in both auditory sensory-intake tasks (listening to randomly generated 'tunes') and internally directed attention tasks (imagining the same randomly generated tunes) matched for auditory input. Measures of evoked (phase locked) and induced (non-phase locked) activity were compared between tasks. Increases in induced alpha power were found during internal attention. No experimental effects were observed for evoked activity. These results are not entirely consistent with proposals that 'paradoxical' alpha indexes the evoked inhibition of task irrelevant processing.
[show abstract][hide abstract] ABSTRACT: One developing theme in consciousness research is that consciousness is not the product of any specific component of the brain, rather it is an emergent property of the changing patterns of connectivity between different specialised functional components. For example, the dynamic core hypothesis proposes that conscious experience requires high levels of neural complexity, where complexity is defined in terms of functional connectivity. To test this hypothesis, electroencephalography was recorded while participants were shown random dot-stereograms. Consistent with the dynamic core hypothesis, neural complexity increased as the participants changed from simply viewing the stereogram to consciously perceiving the hidden 3D image.
International Journal of Psychophysiology 05/2003; 48(1):35-42. · 2.04 Impact Factor
[show abstract][hide abstract] ABSTRACT: Although slow waves of the electroencephalogram (EEG) have been associated with attentional processes, the functional significance of the alpha component in the EEG (8.1-12 Hz) remains uncertain. Conventionally, synchronisation in the alpha frequency range is taken to be a marker of cognitive inactivity, i.e. 'cortical idling'. However, it has been suggested that alpha may index the active inhibition of sensory information during internally directed attentional tasks such as mental imagery. More recently, this idea has been amended to encompass the notion of alpha synchronisation as a means of inhibition of non-task relevant cortical areas irrespective of the direction of attention. Here we test the adequacy of the one idling and two inhibition hypotheses about alpha. In two experiments we investigated the relation between alpha and internally vs. externally directed attention using mental imagery vs. sensory-intake paradigms. Results from both experiments showed a clear relationship between alpha and both attentional factors and increased task demands. At various scalp sites alpha amplitudes were greater during internally directed attention and during increased load, results incompatible with alpha reflecting cortical idling and more in keeping with suggestions of active inhibition necessary for internally driven mental operations.
International Journal of Psychophysiology 02/2003; 47(1):65-74. · 2.04 Impact Factor
[show abstract][hide abstract] ABSTRACT: We examined two subjectively distinct memory states that are elicited during recognition memory in humans and compared them in terms of the gamma oscillations (20-60 Hz) in the electroencepahalogram (EEG) that they induced. These subjective states, 'recollection' and 'familiarity' both entail correct recognition but one involves a clear and conscious recollection of the event including memory for contextual detail whilst the other involves a sense of familiarity without clear recollection. Here we show that during a verbal recognition memory test, the subjective experience of 'recollection' induced higher amplitude gamma oscillations than the subjective experience of 'familiarity' in the time period 300-500 ms after stimulus presentation. Recollection, but not familiarity, was also associated with greater functional connectivity in the gamma frequency range between frontal and parietal sites. Furthermore, the magnitude of the gamma functional connectivity varied over time and was modulated at 3 Hz. Previous studies in animals have shown local theta frequency modulation (3-7 Hz) of gamma-oscillations but this is the first time that a similar effect has been reported in the human EEG.
International Journal of Psychophysiology 12/2002; 46(2):91-100. · 2.04 Impact Factor
[show abstract][hide abstract] ABSTRACT: Mobile phones (MP) are used extensively and yet little is known about the effects they may have on human physiology. There have been conflicting reports regarding the relation between MP use and the electroencephalogram (EEG). The present study suggests that this conflict may be due to methodological differences such as exposure durations, and tests whether exposure to an active MP affects EEG as a function of time.
Twenty-four subjects participated in a single-blind fully counterbalanced cross-over design, where both resting EEG and phase-locked neural responses to auditory stimuli were measured while a MP was either operating or turned off.
MP exposure altered resting EEG, decreasing 1-4 Hz activity (right hemisphere sites), and increasing 8-12 Hz activity as a function of exposure duration (midline posterior sites). MP exposure also altered early phase-locked neural responses, attenuating the normal response decrement over time in the 4-8 Hz band, decreasing the response in the 1230 Hz band globally and as a function of time, and increasing midline frontal and lateral posterior responses in the 30-45 Hz band.
Active MPs affect neural function in humans and do so as a function of exposure duration. The temporal nature of this effect may contribute to the lack of consistent results reported in the literature.
[show abstract][hide abstract] ABSTRACT: Exposure to active mobile phones (MP) has been shown to affect human neural function as shown by the electroencephalogram (EEG). Although it has not been determined whether such effects are harmful, a number of devices have been developed that attempt to minimize these MP-related effects. One such device, the Q Link Ally (QL; Clarus Products, International, L.L.C., San Rafael, CA), is argued to affect the human organism in such a way as to attenuate the effect of MPs. The present pilot study was designed to determine whether there is any indication that QL does alter MP-related effects on the human EEG.
Twenty-four (24) subjects participated in a single-blind, fully counterbalanced crossover design in which subjects' resting EEG and phase-locked neural responses to auditory stimuli were assessed under conditions of either active MP or active MP plus QL.
The addition of QL to the MP condition increased resting EEG in the gamma range and did so as a function of exposure duration, and it attenuated MP-related effects in the delta and alpha range (at trend-level). The addition of the QL also affected phase-locked neural responses, with a laterality reversal in the alpha range and an alteration to changes over time in the delta range, a reduction of the MP-related beta decrease over time at fronto-posterior sites, and a global reduction in the gamma range that increased as a function of exposure duration. No unambiguous relations were found between these changes and either performance or psychologic state.
This pilot study suggests that the addition of the QL to active MP-exposure does affect neural function in humans, altering both resting EEG patterns and the evoked neural response to auditory stimuli, and that there is a tendency for some MP-related changes to the EEG to be attenuated by the QL.
The Journal of Alternative and Complementary Medicine 09/2002; 8(4):427-35. · 1.46 Impact Factor
[show abstract][hide abstract] ABSTRACT: Although memory has been widely studied using event-related potentials, memory-related changes in the electroencephalogram (EEG) have been relatively neglected. The aim of this study was to determine whether evidence could be found for memory-related changes in the EEG. EEG was recorded from a sample of healthy volunteers while they performed word and face recognition memory tasks. Data were analyzed using the method of event-related desynchronization. In the theta frequency range there was a short-duration increase in power that occurred in the first 250 ms that was maximal at temporal sites (T5/T6). For words, but not faces, there was a repetition effect in theta such that new words elicited greater synchronization than old words at the midline frontal electrode (Fz). In the alpha frequency range there was a lateralized repetition effect, which occurred from 750 ms. In upper alpha this effect was lateralized in the expected way with greater desynchronization at temporo-parietal sites on the left for words and on the right for faces. For lower alpha, the lateralization was reversed. The meanings of these findings are interpreted in the light of existing models of recognition memory.
[show abstract][hide abstract] ABSTRACT: Work-related psychological distress (burnout) is a probable cause of drop-out among emotional support volunteers (buddies) who work with people living with AIDS. In addition to the emotional suffering and disruption to both the buddy and the buddied, burnout has significant cost implications for voluntary organizations in terms of training and recruitment. The aim of this study was to identify the demographic, situational and motivational factors associated with burnout among buddies with the intention of identifying individuals at risk at the recruitment stage. A cross-sectional single cohort postal questionnaire study design was used. All buddies registered with the Terrence Higgins Trust, a non-profit making organization set up in the UK to provide education about HIV/AIDS and care for people affected by the virus, were invited to participate. Psychological morbidity was measured with the Hospital Anxiety and Depression Scale, burnout with the Maslach Burnout Inventory and motivation was assessed using the Calvert Motivation Checklist. Information on the buddy relationship and the demographic details of each buddy was also collected. Of 586 questionnaires distributed, 324 (55%) were returned. More than 24% of buddies were classified as probable cases of burnout on one or more of the MBI scales but this is lower than has been reported in medical and nursing staff working with people living with AIDS. Although a number of demographic, situational and motivational factors were associated with burnout, logistic regression models were unable to identify a useful proportion of individuals at risk. It was concluded that although burnout is an important psychological factor in retaining volunteers, it was not possible to identify individuals at risk of burning out either from their self-reported motivations or from demographic factors.
AIDS Care 05/1998; 10(2):175-90. · 1.60 Impact Factor
[show abstract][hide abstract] ABSTRACT: If topographical EEG is to be a useful tool for localising cerebral processes, then the results of the same, or closely similar experiments, using different samples should yield similar results. Although the reliability of EEG is well established in other ways, there is little available data on the reproducibility of EEG topography across experiments. The aim of this study was to determine the reproducibility of topographical EEG by comparing the results of two independently conducted experiments. EEG was recorded during an Eyes Open baseline and a motor task condition (the Luria finger opposition task) in two independent samples of healthy subjects. EEG was recorded in 2.56-s epochs and analysed by FFT into conventional theta, alpha and beta 1 frequency bands. The EEG amplitude for each subject in each frequency range was averaged over a minimum of 60 s. Separate group averages for each sample were calculated and the resulting topographical distributions of electrical potential and current density were compared. The results indicated that the reproducibility of electrical potential in the theta and beta 1 frequency ranges was extremely poor and only approached acceptable levels in alpha. Reproducibility of current source density was poor in all frequency ranges. Although some improvement in reproducibility was obtained following spatial smoothing for alpha potential, the highest reproducibility achieved was only 0.65. Reasons for the poor reproducibility of topographical EEG and the implications of these findings are discussed.
International Journal of Psychophysiology 07/1997; 26(1-3):113-9. · 2.04 Impact Factor
[show abstract][hide abstract] ABSTRACT: Structures within the medial temporal lobe, particularly the hippocampus, have long been implicated in human episodic memory. The same structures are known to generate EEG in the theta frequency range in animals. The aim of this experiment was to investigate the time course of changes in the human theta rhythm during a word recognition memory task. In the period 125-250 ms after the visual presentation of a word, theta power increased by an average of 13% compared with the prestimulus baseline period and this increase was more than twice as great for repeated words (18%) as for new ones (8%). These results show that there are short duration changes in the human theta rhythm associated with recognition memory.
[show abstract][hide abstract] ABSTRACT: HIV-1 infection may be complicated by a number of psychopathological conditions. While organic mental disorders, such as HIV-related psychosis and dementia, are late manifestations, mood disorders may occur during both asymptomatic and symptomatic stages of infection. The possible impact of brain involvement due to neurotropism of HIV-1 has not been investigated systematically in these latter conditions. The psychiatric caseness of HIV-seropositive individuals without AIDS and seronegative controls was assessed using a standardized clinical interview (Present State Examination). A comparison was made between individuals with and without psychiatric caseness using clinical, neuropsychological, and neurophysiological assessments. An increased prevalence of current psychiatric illness was found in subjects with early symptomatic HIV infection compared to those with asymptomatic infection and controls. This could not be attributed to psychiatric history, as well as to clinical and immunological markers of HIV infection, however, psychiatric caseness in early symptomatic infection was associated with marked neurophysiological changes, detectable by quantitative electroencephalography. Altogether, this study provided preliminary evidence that psychiatric symptoms in symptomatic but not asymptomatic HIV infection may be associated with subtle brain involvement preceding the immunological and neurocognitive impairment characteristic for AIDS.
[show abstract][hide abstract] ABSTRACT: The aim of this study was to explore the ability of epoch-averaged electroencephalogram (EEG) to localize cognitive functions. The EEG was recorded in healthy individuals performing a task where, on the basis of evidence from other functional brain imaging techniques, there was a high expectation of where functional changes would be expected. Topographical EEG was recorded while individuals performed recognition memory tasks for words and faces. Comparison of the acquisition and recognition phases of the experiment showed significant attenuation of alpha, beta 1, and beta 2 in the right temporoparietal region for the faces but no significant changes for words. Left temporoparietal changes for the word task were only seen among the women. The results confirmed the validity of EEG for use in the localization of cognitive function for faces for men and women but in the case of words for the women only.
[show abstract][hide abstract] ABSTRACT: To assess the reliability and validity of an HIV-specific quality of life (QoL) questionnaire for use with injecting drug users (IDU).
One hundred IDU with HIV infection (27 asymptomatic, 48 symptomatic, 25 with AIDS) completed the HIV adaptation of the Medical Outcomes Study questionnaire (MOS-HIV). Validity of the scale was assessed by comparing the scores on the MOS-HIV with measures of health and psychological status. Measures of health status used included Centers for Disease Control and Prevention (CDC) stage, CD4 cell count and number of HIV-related illnesses. Psychological status was assessed using the Hospital Anxiety and Depression Scale. Sociodemographic data and information on illegal drug consumption were also collected.
The MOS-HIV showed a good internal reliability on all scales and the factor structure was comparable with that reported from previous studies. The psychological scales from the MOS-HIV showed good concurrent validity. For the physical aspects of QoL, however, some scales were poor at discriminating between different HIV disease stages. One reason for this may have been that factors associated with a history of injecting drug use had a significant negative impact on QoL, particularly for asymptomatic patients. It was notable that QoL in asymptomatic infection was found to be substantially lower than has been reported for gay/bisexual men using the same instruments and was more strongly associated with factors related to drug use rather than to HIV disease status.
The MOS-HIV is a reliable and valid measure, but in patients with a history of injecting drug use some of the scales measuring the physical aspects of QoL may be relatively insensitive to changes in health.
AIDS 01/1997; 10(14):1699-705. · 6.41 Impact Factor
[show abstract][hide abstract] ABSTRACT: The aim of this study was to examine the spatio-temporal reliability of EEG power during the baseline period of an event-related desynchronisation (ERD) experiment. The data were analysed using ideas from generalisability theory. The largest sources of variance were found to be associated with differences between subjects (subject main effect), and to idiosyncratic topographical distributions (subject x electrode interaction). The resulting spatio-temporal reliabilities exceeded 0.7, except in theta and the absolute power values were relatively stable. Overall, this study gives further support for the reliability of quantitative EEG measures in general and for the method of ERD in particular.
International Journal of Psychophysiology 11/1996; 23(3):163-9. · 2.04 Impact Factor
[show abstract][hide abstract] ABSTRACT: Prospective relations between individual differences in both lateralised neuro-psychophysiological functions and mood ratings with immune status (CD4 and CD8 counts) were examined in asymptomatic HIV-positive men (n = 27) over thirty months. They participated in a controlled study of zidovudine versus placebo (results published elsewhere). Measures included EEG spectra, neuropsychological tests and mood ratings. A model of reciprocal lateralised influences on the immune system was tested whereby patients with left superior to right hemispheric functions were predicted to show a less deleterious outcome than those with the opposite asymmetry pattern. Prospective relations with immune status were found in the EEG with lateralised theta, alpha and beta activity; among cognitive measures with word fluency, semantic processing, and lateralised motor and recognition memory (word/face) processes; with mood ratings including depression, confusion and the total mood score. The nature of the effects supported the laterality predictions. These unique data, showing that neuro-psychophysiological factors in HIV+ but otherwise healthy subjects predict immune competence and compromise present 2-3 years later, warrant replication in a larger cohort.
International Journal of Psychophysiology 11/1996; 23(3):215-24. · 2.04 Impact Factor
[show abstract][hide abstract] ABSTRACT: HIV infection is associated with substantial psychological and social morbidity, although there is a dearth of studies of women with the infection. In recent years, developed countries have reported an increase in the prevalence of HIV infection in women, a fact that makes it all the more important to address the study of their psychological and social status. The study is a controlled investigation of HIV seropositive (n = 49) and seronegative women (n = 43), including study of psychological status and history, social functioning and perceived supports, coping style, life events, and sexual difficulties. The results show that about a third of women were psychiatric cases, regardless of HIV status, although more than half of symptomatic women were psychiatric cases. Seropositive women were less likely to use instrumental social supports and more likely to use mental disengagement as ways of coping. Regarding perceived social supports, positive women had lower scores on social integration and guidance. Positive women were more likely to experience sexual difficulties and not to be in a relationship. Negative women reported more adverse life events in the last 6 months. Psychiatric morbidity was associated with poorer social adjustment and more adverse life events, but not with serostatus. HIV positive women and those at risk of HIV infection have substantial levels of psychological and social morbidity that require recognition by those involved in their care and provision of adequate mental health intervention.
Journal of Psychosomatic Research 08/1996; 41(1):39-47. · 3.27 Impact Factor
[show abstract][hide abstract] ABSTRACT: Psychological stress and work-related burnout in staff working with AIDS and with cancer patients were compared using a self-report method of assessment. Measures included the General Health Questionnaire (GHQ), Maslach Burnout Inventory (MBI), and the Social Adjustment Scale (SAS-M). More than 80% of those staff who were approached responded to the questionnaire, including 70 doctors and nurses working with people with AIDS and 41 doctors and nurses working in oncology. More than a third of staff had substantial levels of psychological morbidity, and about a fifth had significant levels of work-related stress. Factors associated with the presence of high levels of psychological morbidity and with abnormal levels of emotional exhaustion, depersonalization, and concerns about personal accomplishment were identified. Staff described the work situations with which they had difficulty dealing and some of the coping strategies they used. The findings confirm that staff working with people with cancer or AIDS experience psychological difficulties of the kind likely to respond to interventions aimed at improving their ability to cope with work-related stresses. The mental health services could play an important role in carrying out research in this field and in providing practical help to deal with staff's difficulties.
Journal of Psychosomatic Research 05/1996; 40(4):425-35. · 3.27 Impact Factor
[show abstract][hide abstract] ABSTRACT: The effect of early antiretroviral medication with zidovudine on neurophysiological functions was evaluated in subjects with asymptomatic HIV-1 infection. Patients were recruited participants of a larger double-blind randomised placebo-controlled treatment trial with zidovudine (Concorde). The main outcome measures included: quantitative electroencephalography (QEEG), auditory event-related potentials (AEP) and pattern-reversal visual evoked potentials (PRVEP), as well as standard clinical, virological and immunological markers. No significant impairment and no difference between treatment groups was found in visual P100 latency and auditory long-latency P3 responses which is in agreement with the absence of neurological and neuropsychological impairment over the study period. Significant treatment effects were revealed by quantitative electroencephalography (QEEG). While the placebo group showed a significant increase in delta and theta slow frequency QEEG activity over the study period, slow wave amplitude remained unchanged in the zidovudine group after a mean follow-up period of 28 months. In summary, the data provide evidence for a low level neuropathological process in asymptomatic HIV-1 infection which can be effectively suppressed by antiretroviral medication.
Journal of the Neurological Sciences 11/1995; 132(2):162-9. · 2.24 Impact Factor