1,721,022 research outputs found
Modulating neural plasticity with non-invasive brain stimulation in schizophrenia
No full textSchizophrenia is a severe mental disorder characterised by a complex phenotype including positive, negative, affective and cognitive symptoms. Various theories have been developed to integrate the clinical phenotype into a strong neurobiological framework. One theory describes schizophrenia as a disorder of impaired neural plasticity. Recently, non-invasive brain stimulation techniques have garnered much attention to their ability to modulate plasticity and treat schizophrenia. The aim of this review is to introduce the basic physiological principles of conventional non-invasive brain stimulation techniques and to review the available evidence for schizophrenia. Despite promising evidence for efficacy in a large number of clinical trials, we continue to have a rudimentary understanding of the underlying neurobiology. Additional investigation is required to improve the response rates to non-invasive brain stimulation, to reduce the interindividual variability and to improve the understanding of non-invasive brain stimulation in schizophrenia
Working Memory Mediates the Association between Dorsolateral Prefrontal Cortex Plasticity and Global Cognition in Alzheimer's Dementia and Older Healthy Comparison Individuals
Full text linkBackgroundDorsolateral prefrontal cortex (DLPFC) plasticity is associated with working memory (WM) in a combine sample of individuals with Alzheimer’s dementia (AD) and older healthy comparison (HC). We hypothesized that DLPFC plasticity is associated with Global Cognition (GC) and that this association is mediated by WM.
MethodsThirty-two AD and 20 HC participants were assessed using Repeatable Battery for the Assessment of Neuropsychological Status for GC, N-back task for WM, and electroencephalography combined with Paired Associative Stimulation of DLPFC for DLPFC plasticity.
ResultsDLPFC plasticity was associated with GC (B [SE] = 21.65 [9.08]; β = 0.30; P = .02) in the combined group of AD and HC participants. WM mediated the association between DLPFC plasticity and GC (B= 18.67[6.52], 99%CI [2.11, 38.94).
Conclusion
This study suggests that DLPFC plasticity impacts GC via its impact on WM and significant relationship between DLPFC plasticity and GC may be mediated by WM.M.Sc
Long-term Functional Brain Outcomes in Children and Adolescents with Enterovirus-A71 Central Nervous System Involvement: A Multi-Echo Resting-State Functional Magnetic Resonance Imaging Study
No full textBACKGROUND: Enterovirus-A71 (EV-A71) is a significant public health concern, particularly in the Asian-Pacific region, given its potential life-altering central nervous system (CNS) infections with neuropsychiatric consequences. Despite literature connecting EV-A71 CNS infections to later attention-deficit/hyperactivity disorder (ADHD) development, there have been no longitudinal follow-up studies on brain features in this special population. As the world-first study, we aimed to investigate the functional connectivity of the midbrain and striatum, functional connectome in children and adolescents with EV-A71-facilitated ADHD, and brain-behavior relationships in children and adolescents with EV-A71 CNS infection earlier in life. METHODS: This naturalistic longitudinal cohort included 31 children and adolescents (aged 6.7-18.3 years) previously infected with the EV-A71 CNS infection (6.0-17.5 years ago), with 16 later developing ADHD. Comparison groups consisted of 53 age- and sex-match participants with idiopathic ADHD and 37 neurotypical (typically developing) participants. All participants received multi-echo resting state fMRI, followed by both seed-based and whole-brain connectome-based analyses. The brain-behaviour relationships within EV-A71-infected participants were also examined. RESULTS: EV-A71-facilitated ADHD participants displayed reduced functional connectivity within the midbrain and striatum compared to EV-A71-infected participants without ADHD. Connectome analysis revealed lower connectivity within task-positive networks compared to idiopathic ADHD. Brain-behaviour analysis showed connectivity between major brain networks was linked to ADHD and autistic symptoms and sustained attention performance. CONCLUSION: Our results highlight potential differences in dopamine circuitry and greater levels of deviant connectivity within the default mode (DMN) network of EV-A71-facilitated ADHD children and adolescents. Future sufficiently powered studies are needed to declare definitive long-term sequelae post EV-A71 CNS infection. Keywords: Enterovirus A71, attention-deficit/hyperactivity disorder, resting-state functional MRI, multi-echo functional MRI, functional connectivity, naturalistic longitudinal follow-up study.M.Sc
Neurophysiological Features of Working Memory Performance and their Relationships with Demographic, Clinical, Genetic, Neurochemical, and Neuro-structural Characteristics in Older Adults at Risk for Dementia
Full text linkTheta gamma coupling (TGC) is a neurophysiological mechanism of working memory (WM). However, the relative contributions of TGC and clinical, demographic, and biological characteristics to WM performance, and the relationship between TGC and these characteristics, remains unclear. Older participants at-risk for Alzheimer’s dementia completed N-back-EEG, genetic testing, PET scan and brain MRI. Linear regressions were used to assess the relationships among 2-back WM performance; demographic and clinical variables; TGC; ApoE4 carrier status; β-amyloid SUVR; and regional cortical thickness, subcortical volumes, and white matter fractional anisotropy. Our results demonstrate that TGC and age are strongly associated with 2-back WM performance. Analyses with additional WM features- theta event-related synchronization (ERS) and alpha event-related desynchronization (ERD)- revealed that neither theta ERS nor alpha ERD were associated with WM performance or any other characteristics. Our findings underline the strong association between WM and TGC, which may represent a mechanism of cognitive reserve.M.Sc
Investigating Causal Relations between EEG Features and Working Memory
Full text linkWorking memory is essential to perform higher-order complex cognitive tasks. A deficit in working memory yields difficulties in performing daily activities and it is an indicator of cognitive decline. Thus, extensive research has focused on approaches to improve working memory. Among these approaches non-invasive brain stimulation (NIBS) has been widely explored. However, the efficiency and reliability of NIBS across studies have not been well established. One reason could be intervening the improper neurophysiological mechanisms of working memory across individuals. Ultimately, for an optimum NIBS, it is essential to target personalized neurophysiological mechanisms that have causal relations to performance. Therefore, the overall objective of my thesis is to use electroencephalography (EEG) signals that recorded while performing N-back working memory task to determine novel neurophysiological targets for NIBS for improving performance.In the first study, we assessed the relative roles of three EEG markers that represent distinct neurophysiological mechanisms of working memory. We investigated the roles of theta-gamma coupling (TGC) representing ordering of information, alpha event-related de-synchronization (ERD) representing interference inhibition, and theta event-related synchronization (ERS) representing cognitive control in preforming N-back. The results of this study demonstrate that TGC could be a potential target for NIBS as it shows an association with N-back performance independent of other EEG markers in both younger and older healthy adults. In the second study, to identify potential targets for personalized NIBS, we used a machine learning-based approach to identify individual-specific neurophysiological correlates of N-back performance. We identified distinct EEG markers, including ERD and ERS from various oscillations and brain regions that predict performance at the individual level. In the third study, to further optimize the targets for personalized NIBS, we used a graphical causal model to identify individual-specific neurophysiological features that cause the performance. The results of this study suggest that entraining gamma oscillations using multiple electrodes over the temporal cortex to generate more causal gamma oscillations and not necessarily increasing the power of these oscillations could result in more effective NIBS outcomes and improvement in N-back performance. Taken together, our findings provide novel targets for personalized NIBS to improve working memory performance and cognition.Ph.D
Validity and Utility of Theta-Gamma Coupling as a Marker of Ordering of Information in Older Adults
Full text linkOrdering of information is a critical component of many everyday tasks, such as remembering a phone number or following directions. Prefrontal cortex theta phase-gamma amplitude coupling (TGC) is a neurophysiologic measure associated with ordering of information during the N-back, a working memory task. Prefrontal cortex TGC could be a target for intervention to improve ordering of information, as past research in both humans and animals suggests there is a strong association between TGC and ordering information of multi-item messages. However, further research is needed confirm this relationship in humans. The overall aim of this thesis is to further examine the relationship between prefrontal cortex TGC as recorded by scalp EEG and ordering of information. We began by determining if the relationship between TGC and ordering exists independent of cognitive task and clinical condition. We then examined the association between changes in TGC and changes in working memory performance over time. Lastly, we examined the utility of using a TGC cut-off to create distinct groups with regards to their cognitive function. The results of the first study demonstrate that TGC is associated with performance on ordering-based cognitive tasks that were completed outside of TGC measurement. In addition, there was no interaction between TGC and diagnosis. These results suggest that the relationship between TGC and ordering exists independent of task and clinical condition. The results of the second study demonstrate a longitudinal relationship between change in TGC and change in working memory performance over 6 to 12 weeks, which suggests that TGC is a stable marker of working memory performance over time. The results of the third study indicate that using a TGC cut-off creates more distinct groups with respect to global cognition compared to diagnosis. Individuals with MCI and MCI+MDD have similar, overlapping cognitive profiles, however, those with low TGC have distinct global cognition compared to those with high TGC. Taken together, these findings provide support for using TGC as a potential marker of intervention to improve cognitive function, and potentially slow or prevent cognitive decline.Ph.D
Investigating Electroencephalogram Microstates in Older Adults at Risk for Dementia
Full text linkElectroencephalogram (EEG) microstates are brief, stable patterns of scalp potential reflecting large-scale brain network activity. This thesis evaluated microstates as potential neurophysiological markers of cognitive impairment in older adults with Mild Cognitive Impairment (MCI), remitted Major Depression Disorder (rMDD), and comorbid rMDD with MCI. Three investigations were conducted: (1) a systematic review and meta-analysis revealed consistent alterations in microstate B dynamics in Alzheimer’s disease and MCI; (2) a cross-sectional EEG study found no significant group differences in microstate B or D, though a sex difference in microstate C duration emerged; and (3) a moderation analysis showed no significant predictive effects of microstates on cognitive outcomes following cognitive remediation and transcranial direct current stimulation. These null results, in a relatively large sample, highlight the challenges of trait and state distinctions, analytic variability, and population heterogeneity. Future research integrating task-based paradigms, individualized decomposition, and biomarker data to improve sensitivity and clinical utility.M.Sc
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
EEG Features of Working Memory Impairment in Alzheimer’s Dementia and Mild Cognitive Impairment
Full text linkThe presence of working memory impairments in individuals with Alzheimer’s Dementia (AD) or Mild Cognitive Impairment (MCI) is well-accepted; however, the neurophysiological mechanisms contributing to these impairments have not been fully elucidated. Research has reliably shown that oscillatory activity, driven by repetitive and synchronous activity within and between neuronal populations, plays a significant role in memory functioning and can be accurately captured using electroencephalography (EEG). While resting-state studies have identified aberrant oscillatory activity, mainly in those with AD, there is a paucity of research investigating how EEG activity behaves during cognitive processing. As such, the overall objective of this study was to assess the relationship between oscillatory activity and working memory impairments in AD and MCI, with a focus on three EEG features: theta and alpha power, theta-gamma coupling, and theta phase synchronization. We hypothesized that these EEG features would be most impaired in those with AD, while individuals with MCI would present with less significant impairments. Additionally, we hypothesized that each of these features would be associated with working memory performance. In the first study, we found that the AD group demonstrated the smallest increase in theta power following the onset of the 2-back stimulus; while compared to controls, the MCI group demonstrated a smaller increase in theta power on the most difficult 3-back condition. Similarly, in the second study, the AD group demonstrated the lowest level of theta-gamma coupling followed by MCI and HC groups. Finally in the third study, we found that the AD group demonstrated impaired theta phase synchronization between the temporal region and the rest of the brain, while no differences were found between the HC and MCI groups. Our results also demonstrated that each of the EEG features were associated with working memory performance to varying degrees. Taken together, findings from these studies revealed widespread impairments in EEG activity in AD, along with an intermediate and inconsistent level of impairment in those with MCI. Ultimately, this research advances our understanding of the neurophysiological mechanisms underlying working memory impairments in MCI and AD and may help guide the development of novel interventions in the future.Ph.D
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