Publications by authors named "Hugh Nolan"

Article Synopsis
  • Ketamine, a dissociative anesthetic, alters global consciousness states and brain dynamics, with the study investigating its effects using portable low-density EEG systems instead of traditional methods.
  • The study involved 30 male adults in a double-blinded experiment comparing ketamine and saline, analyzing both resting-state and task-driven EEG, finding that ketamine increases redundancy in brain dynamics, especially at alpha frequencies.
  • High-order interactions (HOI) revealed that ketamine correlates with dissociative experiences and offers a novel approach to studying brain connectivity and dynamics during drug interventions.
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Article Synopsis
  • A study involving 30 young adult males utilized a double-blinded crossover design to investigate the effects of racemic ketamine compared to saline infusion on brain dynamics through EEG recordings.
  • Ketamine was found to increase redundancy in brain activity, especially in the alpha frequency band, and this effect was more pronounced in a resting state, indicating a shift towards dissociative states of consciousness.
  • The study introduces Higher Order Interactions (HOI) as a promising method for analyzing EEG data, highlighting its capability to reveal how different electrode interactions may be associated with experiences like derealization and changes in consciousness due to drug interventions.
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Recent advances have enabled the creation of wireless, "dry" electroencephalography (EEG) recording systems, and easy-to-use engaging tasks, that can be operated repeatedly by naïve users, unsupervised in the home. Here, we evaluated the validity of dry-EEG, cognitive task gamification, and unsupervised home-based recordings used in combination. Two separate cohorts of participants-older and younger adults-collected data at home over several weeks using a wireless dry EEG system interfaced with a tablet for task presentation.

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Aims: Cerebral hypoperfusion is implicated in the pathogenesis of associations between orthostatic hypotension and adverse outcome such as falls, cognitive impairment, depression, and mortality. Although the blood pressure response to orthostasis has been well studied there is a lack of information on orthostatic cerebrovascular responses in older populations.

Methods And Results: We measured cerebral hemodynamics, utilizing near infrared spectroscopy, coupled with peripheral blood pressure during an active stand in a large population of well-phenotyped older adults (N = 2764).

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Access to affordable, objective and scalable biomarkers of brain function is needed to transform the healthcare burden of neuropsychiatric and neurodegenerative disease. Electroencephalography (EEG) recordings, both resting and in combination with targeted cognitive tasks, have demonstrated utility in tracking disease state and therapy response in a range of conditions from schizophrenia to Alzheimer's disease. But conventional methods of recording this data involve burdensome clinic visits, and behavioural tasks that are not effective in frequent repeated use.

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Objective: Cognitive impairment is prevalent in older ages. Associations with sleep are well established; however, ambiguity remains in which sleep characteristics contribute to this impairment. We examined cross-sectional associations between both self-reported and actigraphy-based sleep and cognitive performance across a number of domains in community-dwelling older adults.

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Objectives: To establish agreement between self-reported and actigraphy-based total sleep time (TST). To determine the impact of self-reported sleep problems on these measurements.

Design: Cross-sectional study using data from Wave 3 of The Irish Longitudinal Study on Ageing (2014-2015).

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Assessment of the cerebrovascular and cardiovascular response to standing has prognostic value for a range of outcomes in the older adult population. Studies generally attempt to control for standing speed differences by asking participants to stand in a specified time but little is known about the range of transition times observed. This study aimed to characterize how standing speed associates with cardiovascular and cerebrovascular measures following transition from supine to standing.

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Aims: Near-infrared spectroscopy (NIRS) is a non-invasive, easy to apply, optical technology for measuring cerebral blood oxygenation, but there is lack of comprehensive population data to aid interpretation and clinical use. Given the importance of cerebral perfusion in the context of evolving guideline recommendations for more aggressive lowering of blood pressure (BP) in hypertension, even in the oldest old, understanding of normative NIRS values is timely. We estimated normative values of cerebral oxygenation measured by NIRS in a large community-dwelling population sample of adults aged > = 50 years (n = 3110).

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Objective: This study assessed the distribution and correlates of objective sleep duration in the older population in Ireland.

Design: Cross-sectional study using population-derived data from wave 3 of The Irish Longitudinal Study on Ageing.

Setting: Community-dwelling adults.

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The heterogeneous specialisation of hippocampal subfields across memory functions has been widely shown in animal models. Yet, few in vivo studies in humans have explored correspondence between hippocampal subfield anatomy and memory performance in ageing. Here, we used a well-validated automated MR segmentation protocol to measure hippocampal subfield volumes in 436 non-demented adults aged 50+.

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Background: Deficits in frontal lobe perfusion have been demonstrated in late-life depression; however, studies to date have generally involved small numbers, used neuroimaging rather than bedside testing and have not controlled for important covariates.AimsWe aimed to examine the association between depressive symptoms and frontal lobe perfusion during standing, in a large cohort of community-dwelling older people.

Method: Participants aged ≥50 years underwent continuous measurement of orthostatic blood pressure by finometry, and frontal lobe perfusion by near-infrared spectroscopy.

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Ageing is associated with widespread alterations to the brain's anatomy and to attendant cortical networks. Yet, few studies to date have indexed anatomical covariance network differences within the age distribution of older adulthood, despite known phenotypic variation. Here, we explored cortical anatomical covariance networks in middle and older age cross-sectionally, using a large sample of community-dwelling older adults from the Irish Longitudinal Study on Ageing (TILDA).

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Event-related potentials (ERPs) show promise to be objective indicators of cognitive functioning. The aim of the study was to examine if ERPs recorded during an oddball task would predict cognitive functioning and information processing speed in Multiple Sclerosis (MS) patients and controls at the individual level. Seventy-eight participants (35 MS patients, 43 healthy age-matched controls) completed visual and auditory 2- and 3-stimulus oddball tasks with 128-channel EEG, and a neuropsychological battery, at baseline (month 0) and at Months 13 and 26.

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Rationale: Speed of heart rate recovery (HRR) may serve as an important biomarker of aging and mortality.

Objective: To examine whether the speed of HRR after an orthostatic maneuver (ie, active stand from supine position) predicts mortality.

Methods And Results: A longitudinal cohort study involving a nationally representative sample of community-dwelling older individuals aged ≥50 years.

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Conduction along the optic nerve is often slowed in multiple sclerosis (MS). This is typically assessed by measuring the latency of the P100 component of the Visual Evoked Potential (VEP) using electroencephalography. The Visual Evoked Spread Spectrum Analysis (VESPA) method, which involves modulating the contrast of a continuous visual stimulus over time, can produce a visually evoked response analogous to the P100 but with a higher signal-to-noise ratio and potentially higher sensitivity to individual differences in comparison to the VEP.

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Objectives: A high resting heart rate (RHR) represents a major risk factor for cardiovascular disease and individuals from poorer backgrounds have a higher RHR compared with their more advantaged peers. This study investigates the pathways through which low socioeconomic status (SES) contributes to a higher RHR.

Method: The sample involved data for 4,888 respondents who were participating in the first wave of The Irish Longitudinal Study on Ageing.

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Background: In this report, we provide the first normative reference data and prevalence estimates of impaired orthostatic blood pressure (BP) stabilization, initial orthostatic hypotension, and orthostatic hypotension based on beat-to-beat blood pressure methods in a population-representative sample.

Methods And Results: Participants were recruited from a nationally representative cohort study (≥50 years). Beat-to-beat systolic BP, diastolic BP, and heart rate records were analyzed among those who underwent an active stand test (n=4475).

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Resting fluctuations in the blood oxygenation level-dependent signal have attracted considerable interest for their sensitivity to pathological brain processes. However, these analyses are susceptible to confound by nonneural physiological factors such as vasculature, breathing, and head movement which is a concern when investigating elderly or pathological groups. Here, we used simultaneous electroencephalogram (EEG) and functional magnetic resonance imaging (fMRI) (EEG/fMRI) to constrain the analysis of resting state networks (RSNs) and identify aging differences.

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Cognitive impairment (CI), often examined with neuropsychological tests such as the Paced Auditory Serial Addition Test (PASAT), affects approximately 65% of multiple sclerosis (MS) patients. The P3b event-related potential (ERP), evoked when an infrequent target stimulus is presented, indexes cognitive function and is typically compared across subjects' scalp electroencephalography (EEG) data. However, the clustering of independent components (ICs) is superior to scalp-based EEG methods because it can accommodate the spatiotemporal overlap inherent in scalp EEG data.

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The technical challenges of recording electroencephalographic (EEG) data during motion are considerable, but would enable the possibility of investigating neural function associated with balance, motor function and motion perception. The challenges include finding a reliable method of motion stimulus reproduction, removing artifacts, and ensuring that the recordings retain sufficient EEG signal for proper interpretation. This study details the use of the P3 waveform to validate the concept of motion-based EEG data, and discusses some potential future uses in experimental and clinical settings.

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