Multimodal neuroimaging evidence of alterations in cortical structure and function in HIV-infected older adults

A longitudinal study of the brain structure network changes in HIV patients with ANI: combined VBM with SCN

Background

Despite the widespread adoption of combination antiretroviral therapy (cART) in managing HIV, the virus's impact on the brain structure of patients remains significant. This study aims to longitudinally explore the persistent effects of HIV on brain structure, focusing on changes in gray matter volume (GMV) and structural covariance network (SCN) among patients at the Asymptomatic Neurocognitive Impairment (ANI) stage.

Methods

This research involved 45 HIV patients diagnosed with ANI and 45 demographically matched healthy controls (HCs). The participants were observed over a 1.5-year period. Differences in GMV between groups were analyzed using voxel-based morphometry (VBM), while the graph theory model facilitated the establishment of topological metrics for assessing network indices. These differences were evaluated using two-sample t-tests and paired-sample t-tests, applying the network-based statistics method. Additionally, the study examined correlations between GMV and cognitive performance, as well as clinical variables.

Results

Compared with HCs, HIV patients demonstrated reduced GMV in the right middle temporal gyrus and left middle frontal gyrus (FWE, p < 0.05), along with decreased betweenness centrality (BC) in the left anterior cingulate and paracingulate cortex. Conversely, an increase in the clustering coefficient (Cp) was observed (FDR, p < 0.05). During the follow-up period, a decline in GMV in the right fusiform gyrus (FWE, p < 0.05) and a reduction in node efficiency (Ne) in the triangular part of the inferior frontal gyrus were noted compared with baseline measurements (FDR, p < 0.05). The SCN of HIV patients exhibited small-world properties across most sparsity levels (Sigma >1), and area under the curve (AUC) analysis revealed no significant statistical differences between groups.

Conclusion

The findings suggest that despite the administration of combination antiretroviral therapy (cART), HIV continues to exert slow and sustained damage on brain structures. However, when compared to HCs, the small-world properties of the patients' SCNs did not significantly differ, and the clustering coefficient, indicative of the overall information-processing capacity of the brain network, was slightly elevated in HIV patients. This elevation may relate to compensatory effects of brain area functions, the impact of cART, functional reorganization, or inflammatory responses.

Multimodal Approach to Neurocognitive Function in People Living with HIV in the cART Era: A Comprehensive Review

Combination antiretroviral treatment (cART) has revolutionized the management of human immunodeficiency virus (HIV) and has markedly improved the disease burden and life expectancy of people living with HIV. HIV enters the central nervous system (CNS) early in the course of infection, establishes latency, and produces a pro-inflammatory milieu that may affect cognitive functions, even in the cART era. Whereas severe forms of neurocognitive impairment (NCI) such as HIV-associated dementia have declined over the last decades, milder forms have become more prevalent, are commonly multifactorial, and are associated with comorbidity burdens, mental health, cART neurotoxicity, and ageing. Since 2007, the Frascati criteria have been used to characterize and classify HIV-associated neurocognitive disorders (HAND) into three stages, namely asymptomatic neurocognitive impairment (ANI), mild neurocognitive disorder (MND), and HIV-associated dementia (HAD). These criteria are based on a comprehensive neuropsychological assessment that presupposes the availability of validated, demographically adjusted, and normative population data. Novel neuroimaging modalities and biomarkers have been proposed in order to complement NCI assessments, elucidate neuropathogenic mechanisms, and support HIV-associated NCI diagnosis, monitoring, and prognosis. By integrating neuropsychological assessments with biomarkers and neuroimaging into a holistic care approach, clinicians can enhance diagnostic accuracy, prognosis, and patient outcomes. This review interrogates the value of these modes of assessment and proposes a unified approach to NCI diagnosis.

Comparison of Resting State Functional Connectivity in Persons With and Without HIV: A Cross-sectional Study

BACKGROUND

This study examined the effects of human immunodeficiency virus (HIV) on resting state functional connectivity (RSFC) in a large cohort of people with HIV (PWH) and healthy controls without HIV (PWoH). Within PWH analyses focused on the effects of viral suppression and cognitive impairment on RSFC.

METHODS

A total of 316 PWH on stable combination antiretroviral therapy and 209 demographically matched PWoH were scanned at a single institution. Effects of the virus were examined by grouping PWH by detectable (viral load > 20 copies/mL; VLD) and undetectable (VLU) viral loads and as being cognitively impaired (CI) (Global Deficit Score ≥ 0.5) or cognitively normal (CN). Regression analysis, object oriented data analysis, and spring embedded graph models were applied to RSFC measures from 298 established brain regions of interest comprising 13 brain networks to examine group differences.

RESULTS

No significant RSFC differences were observed between PWH and PWoH. Within PWH, there were no significant differences in RSFC between VLD and VLU subgroups and CI and CN subgroups.

CONCLUSIONS

There were no significant effects of HIV on RSFC in our relatively large cohort of PWH and PWoH. Future studies could increase the sample size and combine with other imaging modalities.

Developmental differences in functional organization of multispectral networks

Assessing brain connectivity during rest has become a widely used approach to identify changes in functional brain organization during development. Generally, previous works have demonstrated that brain activity shifts from more local to more distributed processing from childhood into adolescence. However, the majority of those works have been based on functional magnetic resonance imaging measures, whereas multispectral functional connectivity, as measured using magnetoencephalography (MEG), has been far less characterized. In our study, we examined spontaneous cortical activity during eyes-closed rest using MEG in 101 typically developing youth (9-15 years old; 51 females, 50 males). Multispectral MEG images were computed, and connectivity was estimated in the canonical delta, theta, alpha, beta, and gamma bands using the imaginary part of the phase coherence, which was computed between 200 brain regions defined by the Schaefer cortical atlas. Delta and alpha connectivity matrices formed more communities as a function of increasing age. Connectivity weights predominantly decreased with age in both frequency bands; delta-band differences largely implicated limbic cortical regions and alpha band differences in attention and cognitive networks. These results are consistent with previous work, indicating the functional organization of the brain becomes more segregated across development, and highlight spectral specificity across different canonical networks.

Effects of clinical, comorbid, and social determinants of health on brain ageing in people with and without HIV: a retrospective case-control study

BACKGROUND

Neuroimaging reveals structural brain changes linked with HIV infection and related neurocognitive disorders; however, group-level comparisons between people with HIV and people without HIV do not account for within-group heterogeneity. The aim of this study was to quantify the effects of comorbidities such as cardiovascular disease and adverse social determinants of health on brain ageing in people with HIV and people without HIV.

METHODS

In this retrospective case-control study, people with HIV from Washington University in St Louis, MO, USA, and people without HIV identified through community organisations or the Research Participant Registry were clinically characterised and underwent 3-Tesla T1-weighted MRI between Dec 3, 2008, and Oct 4, 2022. Exclusion criteria were established by a combination of self-reports and medical records. DeepBrainNet, a publicly available machine learning algorithm, was applied to estimate brain-predicted age from MRI for people with HIV and people without HIV. The brain-age gap, defined as the difference between brain-predicted age and true chronological age, was modelled as a function of clinical, comorbid, and social factors by use of linear regression. Variables were first examined singly for associations with brain-age gap, then combined into multivariate models with best-subsets variable selection.

FINDINGS

In people with HIV (mean age 44·8 years [SD 15·5]; 78% [296 of 379] male; 69% [260] Black; 78% [295] undetectable viral load), brain-age gap was associated with Framingham cardiovascular risk score (p=0·0034), detectable viral load (>50 copies per mL; p=0·0023), and hepatitis C co-infection (p=0·0065). After variable selection, the final model for people with HIV retained Framingham score, hepatitis C, and added unemployment (p=0·0015). Educational achievement assayed by reading proficiency was linked with reduced brain-age gap (p=0·016) for people without HIV but not for people with HIV, indicating a potential resilience factor. When people with HIV and people without HIV were modelled jointly, selection resulted in a model containing cardiovascular risk (p=0·0039), hepatitis C (p=0·037), Area Deprivation Index (p=0·033), and unemployment (p=0·00010). Male sex (p=0·078) and alcohol use history (p=0·090) were also included in the model but were not individually significant.

INTERPRETATION

Our findings indicate that comorbid and social determinants of health are associated with brain ageing in people with HIV, alongside traditional HIV metrics such as viral load and CD4 cell count, suggesting the need for a broadened clinical perspective on healthy ageing with HIV, with additional focus on comorbidities, lifestyle changes, and social factors.

FUNDING

National Institute of Mental Health, National Institute of Nursing Research, and National Institute of Drug Abuse.

Imaging of Brain Structural and Functional Effects in People With Human Immunodeficiency Virus

Before the introduction of antiretroviral therapy, human immunodeficiency virus (HIV) infection was often accompanied by central nervous system (CNS) opportunistic infections and HIV encephalopathy marked by profound structural and functional alterations detectable with neuroimaging. Treatment with antiretroviral therapy nearly eliminated CNS opportunistic infections, while neuropsychiatric impairment and peripheral nerve and organ damage have persisted among virally suppressed people with HIV (PWH), suggesting ongoing brain injury. Neuroimaging research must use methods sensitive for detecting subtle HIV-associated brain structural and functional abnormalities, while allowing for adjustments for potential confounders, such as age, sex, substance use, hepatitis C coinfection, cardiovascular risk, and others. Here, we review existing and emerging neuroimaging tools that demonstrated promise in detecting markers of HIV-associated brain pathology and explore strategies to study the impact of potential confounding factors on these brain measures. We emphasize neuroimaging approaches that may be used in parallel to gather complementary information, allowing efficient detection and interpretation of altered brain structure and function associated with suboptimal clinical outcomes among virally suppressed PWH. We examine the advantages of each imaging modality and systematic approaches in study design and analysis. We also consider advantages of combining experimental and statistical control techniques to improve sensitivity and specificity of biotype identification and explore the costs and benefits of aggregating data from multiple studies to achieve larger sample sizes, enabling use of emerging methods for combining and analyzing large, multifaceted data sets. Many of the topics addressed in this article were discussed at the National Institute of Mental Health meeting "Biotypes of CNS Complications in People Living with HIV," held in October 2021, and are part of ongoing research initiatives to define the role of neuroimaging in emerging alternative approaches to identifying biotypes of CNS complications in PWH. An outcome of these considerations may be the development of a common neuroimaging protocol available for researchers to use in future studies examining neurological changes in the brains of PWH.

Altered gray matter structural covariance networks in drug-naïve and treated early HIV-infected individuals

Background

While regional brain structure and function alterations in HIV-infected individuals have been reported, knowledge about the topological organization in gray matter networks is limited. This research aims to investigate the effects of early HIV infection and combination antiretroviral therapy (cART) on gray matter structural covariance networks (SCNs) by employing graph theoretical analysis.

Methods

Sixty-five adult HIV+ individuals (25–50 years old), including 34 with cART (HIV+/cART+) and 31 medication-naïve (HIV+/cART–), and 35 demographically matched healthy controls (HCs) underwent high-resolution T1-weighted images. A sliding-window method was employed to create “age bins,” and SCNs (based on cortical thickness) were constructed for each bin by calculating Pearson's correlation coefficients. The group differences of network indices, including the mean nodal path length (Nlp), betweenness centrality (Bc), number of modules, modularity, global efficiency, local efficiency, and small-worldness, were evaluated by ANOVA and post-hoc tests employing the network-based statistics method.

Results

Relative to HCs, less efficiency in terms of information transfer in the parietal and occipital lobe (decreased Bc) and a compensated increase in the frontal lobe (decreased Nlp) were exhibited in both HIV+/cART+ and HIV+/cART– individuals (P &lt; 0.05, FDR-corrected). Compared with HIV+/cART– and HCs, less specialized function segregation (decreased modularity and small-worldness property) and stronger integration in the network (increased Eglob and little changed path length) were found in HIV+/cART+ group (P &lt; 0.05, FDR-corrected).

Conclusion

Early HIV+ individuals exhibited a decrease in the efficiency of information transmission in sensory regions and a compensatory increase in the frontal lobe. HIV+/cART+ showed a less specialized regional segregation function, but a stronger global integration function in the network.

Signatures of somatosensory cortical dysfunction in Alzheimer's disease and HIV-associated neurocognitive disorder

Alzheimer's disease is the most common type of dementia in the general population, while HIV-associated neurocognitive disorder is the most common neurological comorbidity in those infected with HIV and affects between 40 and 70% of this population. Both conditions are associated with cognitive impairment and have been associated with aberrant functioning in sensory cortices, but far less is known about their disparate effects on neural activity. Identifying such disparate effects is important because it may provide critical data on the similarities and differences in the neuropathology underlying cognitive decline in each condition. In the current study, we utilized magnetoencephalography, extensive neuropsychological testing and a paired-pulse somatosensory gating paradigm to probe differences in somatosensory processing in participants from two ongoing magnetoencephalography studies. The resulting participant groups included 27 cognitively normal controls, 26 participants with HIV-associated neurocognitive disorder and 21 amyloid biomarker-confirmed patients with Alzheimer's disease. The data were imaged using a beamformer and voxel time series were extracted to identify the oscillatory dynamics serving somatosensory processing, as well as the amplitude of spontaneous cortical activity preceding stimulation onset. Our findings indicated that people with Alzheimer's disease and HIV-associated neurocognitive disorder exhibit normal somatosensory gating but have distinct aberrations in other elements of somatosensory cortical function. Essentially, those with Alzheimer's disease exhibited accentuated neural responses to somatosensory stimulation, along with spontaneous gamma activity preceding stimulus onset. In contrast, those with HIV-associated neurocognitive disorder exhibited normal responses to somatosensory stimulation but had sharply elevated spontaneous gamma activity prior to stimulus onset. These distinct aberrations may reflect the impact of different neuropathological mechanisms underlying each condition. Further, given the differential pattern of deficits in somatosensory cortical function, these measures may function as unique biomarkers in each condition and be useful in identifying persons with HIV who may go on to develop Alzheimer's disease.

The impacts of HIV infection, age, and education on functional brain networks in adults with HIV

HIV-associated neurocognitive disorders (HAND) remain highly prevalent in people with HIV (PWH). Studies suggested that certain sociodemographic factors are associated with the risk of HAND in PWH. Here we investigated the impact of HIV infection and demographics on functional brain networks. One run of 8.5 min resting state functional MRI (fMRI) data was collected from 101 PWH (41-70 years old) and 40 demographically comparable controls. Functional connectivity (FC) was calculated using average wavelet coherence. The impact of demographic factors on FCs was investigated using canonical correlation analysis (CCA). Wavelet coherence analysis revealed a reduced within-network connectivity in the dorsal somatomotor network (dSMN), along with a reduced between-network connectivity between dSMN and medial temporal lobe (MTL) in PWH (compared to controls). Across all participants, CCA revealed that older age and HIV infection had negative impacts on network connectivity measures (mainly reduced within- and between-network FCs), whereas education had an opposite effect. In addition, being female at birth or a member of a minority ethnic/racial group was also associated with network disruptions. Our data suggested that advanced age and HIV infection are risk factors for functional brain network disruptions, whereas higher educational attainment was linked to better preserved functional network connectivity.

HIV-Associated Structural and Functional Brain Alterations in Homosexual Males

Purpose:

Neuroimaging elucidations have shown structural and functional brain alterations in HIV-infected (HIV+) individuals when compared to HIV-negative (HIV–) controls. However, HIV− groups used in previous studies were not specifically considered for sexual orientation, which also affects the brain structures and functions. The current study aimed to characterize the brain alterations associated with HIV infection while controlling for sexual orientation.

Methods:

Forty-three HIV+ and 40 HIV– homosexual men (HoM) were recruited and underwent resting-state MRI scanning. Group differences in gray matter volume (GMV) were assessed using a voxel-based morphometry analysis. Brain regions with the altered GMV in the HIV+ HoM group were then taken as regions of interest in a seed-based analysis to identify altered functional connectivity. Furthermore, the amplitude of low-frequency fluctuation (ALFF) and regional homogeneity values were compared between the two groups to evaluate the HIV-associated functional abnormalities in local brain regions.

Results:

HIV+ HoM showed significantly increased GMV in the bilateral parahippocampal gyrus and amygdala, and decreased GMV in the right inferior cerebellum, compared with the HIV– HoM. The brain regions with increased GMV were hyper-connected with the left superior cerebellum, right lingual gyrus, and left precuneus in the HIV+ HoM. Moreover, the ALFF values of the right fusiform gyrus, and left parahippocampal gyrus were increased in the HIV+ HoM. The regional homogeneity values of the right anterior cingulate and paracingulate gyri, and left superior cerebellum were decreased in the HIV+ HoM.

Conclusion:

When the study population was restricted to HoM, HIV+ individuals exhibited structural alterations in the limbic system and cerebellum, and functional abnormalities in the limbic, cerebellum, and visual network. These findings complement the existing knowledge on the HIV-associated neurocognitive impairment from the previous neuroimaging studies by controlling for the potential confounding factor, sexual orientation. Future studies on brain alternations with the exclusion of related factors like sexual orientation are needed to understand the impact of HIV infection on neurocognitive function more accurately.

Hepatitis C Virus-Related Central and Peripheral Nervous System Disorders

Hepatitis C Virus (HCV), despite being a hepatotropic virus, is the causative agent of many systemic disorders, such as vasculitis, autoimmune diseases, lymphoproliferative disorders, and a broad spectrum of neurological and psychiatric manifestations. Although symptoms have been misdiagnosed or underdiagnosed, only recently, evidence of direct (inflammatory) or indirect (immune-mediated) HCV-dependent cerebral effects has been established. HCV infection can promote acute inflammatory response, pro-coagulative status and ischemic disorders, and neurodegeneration. These effects rely on cerebral HCV replication, possibly mediated by blood-brain barrier alterations. Further study is needed to better understand the HCV-related mechanisms of brain damage.

Somatosensory dysfunction is masked by variable cognitive deficits across patients on the Alzheimer's disease spectrum

Background

Alzheimer's disease (AD) is generally thought to spare primary sensory function; however, such interpretations have drawn from a literature that has rarely taken into account the variable cognitive declines seen in patients with AD. As these cognitive domains are now known to modulate cortical somatosensory processing, it remains possible that abnormalities in somatosensory function in patients with AD have been suppressed by neuropsychological variability in previous research.

Methods

In this study, we combine magnetoencephalographic (MEG) brain imaging during a paired-pulse somatosensory gating task with an extensive battery of neuropsychological tests to investigate the influence of cognitive variability on estimated differences in somatosensory function between biomarker-confirmed patients on the AD spectrum and cognitively-normal older adults.

Findings

We show that patients on the AD spectrum exhibit largely non-significant differences in somatosensory function when cognitive variability is not considered (p-value range: .020–.842). However, once attention and processing speed abilities are considered, robust differences in gamma-frequency somatosensory response amplitude (p < .001) and gating (p = .004) emerge, accompanied by significant statistical suppression effects.

Interpretation

These findings suggest that patients with AD exhibit insults to functional somatosensory processing in primary sensory cortices, but these effects are masked by variability in cognitive decline across individuals.

Funding

National Institutes of Health, USA; Fremont Area Alzheimer's Fund, USA

Human immunodeficiency virus-related decreases in corpus callosal integrity and corresponding increases in functional connectivity

People living with human immunodeficiency virus (PLWH) often have neurocognitive impairment. However, findings on HIV-related differences in brain network function underlying these impairments are inconsistent. One principle frequently absent from these reports is that brain function is largely emergent from brain structure. PLWH commonly have degraded white matter; we hypothesized that functional communities connected by degraded white matter tracts would show abnormal functional connectivity. We measured white matter integrity in 69 PLWH and 67 controls using fractional anisotropy (FA) in 24 intracerebral white matter tracts. Then, among tracts with degraded FA, we identified gray matter regions connected to these tracts and measured their functional connectivity during rest. Finally, we identified cognitive impairment related to these structural and functional connectivity systems. We found HIV-related decreased FA in the corpus callosum body (CCb), which coordinates activity between the left and right hemispheres, and corresponding increases in functional connectivity. Finally, we found that individuals with impaired cognitive functioning have lower CCb FA and higher CCb functional connectivity. This result clarifies the functional relevance of the corpus callosum in HIV and provides a framework in which abnormal brain function can be understood in the context of abnormal brain structure, which may both contribute to cognitive impairment.

Impact of HIV-infection on human somatosensory processing, spontaneous cortical activity, and cortical thickness: A multimodal neuroimaging approach

HIV-infection has been associated with widespread alterations in brain structure and function, although few studies have examined whether such aberrations are co-localized and the degree to which clinical and cognitive metrics are related. We examine this question in the somatosensory system using high-resolution structural MRI (sMRI) and magnetoencephalographic (MEG) imaging of neural oscillatory activity. Forty-four participants with HIV (PWH) and 55 demographically-matched uninfected controls completed a paired-pulse somatosensory stimulation paradigm during MEG and underwent 3T sMRI. MEG data were transformed into the time-frequency domain; significant sensor level responses were imaged using a beamformer. Virtual sensor time series were derived from the peak responses. These data were used to compute response amplitude, sensory gating metrics, and spontaneous cortical activity power. The T1-weighted sMRI data were processed using morphological methods to derive cortical thickness values across the brain. From these, the cortical thickness of the tissue coinciding with the peak response was estimated. Our findings indicated both PWH and control exhibit somatosensory gating, and that spontaneous cortical activity was significantly stronger in PWH within the left postcentral gyrus. Interestingly, within the same tissue, PWH also had significantly reduced cortical thickness relative to controls. Follow-up analyses indicated that the reduction in cortical thickness was significantly correlated with CD4 nadir and mediated the relationship between HIV and spontaneous cortical activity within the left postcentral gyrus. These data indicate that PWH have abnormally strong spontaneous cortical activity in the left postcentral gyrus and such elevated activity is driven by locally reduced cortical gray matter thickness.

Atypical Resting-State Functional Connectivity Dynamics Correlate With Early Cognitive Dysfunction in HIV Infection

Purpose: Previous studies have shown that HIV affects striato-cortical regions, leading to persisting cognitive impairment in 30-70% of the infected individuals despite combination antiretroviral therapy. This study aimed to investigate brain functional dynamics whose deficits might link to early cognitive decline or immunologic deterioration. Methods: We applied sliding windows and K-means clustering to fMRI data (HIV patients with asymptomatic neurocognitive impairment and controls) to construct dynamic resting-state functional connectivity (RSFC) maps and identify states of their reoccurrences. The average and variability of dynamic RSFC, and the dwelling time and state transitioning of each state were evaluated. Results: HIV patients demonstrated greater variability in RSFC between the left pallidum and regions of right pre-central and post-central gyri, and between the right supramarginal gyrus and regions of the right putamen and left pallidum. Greater variability was also found in the frontal RSFC of pars orbitalis of the left inferior frontal gyrus and right superior frontal gyrus (medial). While deficits in learning and memory recall of HIV patients related to greater striato-sensorimotor variability, deficits in attention and working memory were associated with greater frontal variability. Greater striato-parietal variability presented a strong link with immunologic function (CD4+/CD8+ ratio). Furthermore, HIV-infected patients exhibited longer time and reduced transitioning in states typified by weaker connectivity in specific networks. CD4+T-cell counts of the HIV-patients were related to reduced state transitioning. Conclusion: Our findings suggest that HIV alters brain functional connectivity dynamics, which may underlie early cognitive impairment. These findings provide novel insights into our understanding of HIV pathology, complementing the existing knowledge.

Altered Gray Matter Volume and Functional Connectivity in Human Immunodeficiency Virus-Infected Adults

People living with human immunodeficiency virus (HIV) (PLWH) are at high risk of neurocognitive impairment. The pathogenesis of neurocognitive impairment remains unclear, and there is still no diagnostic biomarker. By coupling three-dimensional T1-weighted imaging and resting-state functional imaging, we explored structural and functional alterations in PLWH and examined whether such imaging alterations had the potential to denote neurocognitive function. A total of 98 PLWH and 47 seronegative controls aged 20-53 years were recruited. Structural alterations were first explored between HIV-negative controls and PLWH. Subsequently, brain regions showing gray matter alterations were used as seeds for separate whole-brain functional connectivity (FC) analysis. Finally, the relationships between imaging alterations and cognitive function were explored. PLWH suffered from thalamus, occipital lobe, and hippocampus/parahippocampus atrophy. Visual cortices in PLWH showed decreased anticorrelation with the posterior cingulate cortex and left angular gyrus of the default mode network. FC within the visual cortices (between the left calcarine and right calcarine) and in the thalamic prefrontal circuit and between the thalamus and somatosensory association cortex were also altered. In addition, FC between the left thalamus and right dorsolateral prefrontal cortex in the cognitively impaired group was significantly different from that in the cognitively normal group in PLWH. Partial correlation analysis uncorrected for multiple comparisons suggested that some imaging alterations can be associated with neurocognition. Our study supports the presence of brain atrophy and functional reconfiguration in PLWH. Imaging alterations can be associated with neurocognitive function. We hold that neuroimaging is a promising approach in evaluating PLWH and might have the potential to clarify the pathogenesis of HIV-associated neurocognitive disorder.

The Prevalence of Frascati-Criteria-Based HIV-Associated Neurocognitive Disorder (HAND) in HIV-Infected Adults: A Systematic Review and Meta-Analysis

Background: The HIV associated mortality is decreasing in most countries due to the widespread use of antiretroviral therapy. However, HIV-associated neurocognitive disorder (HAND) remains a problematic issue that lowers the quality of life and increases the public health burden among people living with HIV. The prevalence of HAND varies across studies and selected samples. Therefore, we aimed to quantitatively summarize the pooled prevalence of Frascati-criteria-based HAND and to explore the potential demographic, clinical, and immunological factors. Methods: A comprehensive literature search in PubMed/Medline, Web of Science, Embase, and PsycINFO was performed. A random-effects meta-analysis was conducted using the event rate (ER) for the estimation of the incidence of HAND. Subgroup meta-analyses were used to evaluate between-group differences in categorical variables. Meta-regression with the unrestricted maximum likelihood (ML) method was used to evaluate associations of continuous variables. Results: Eighteen studies whose sample sizes ranged from 206 to 1555 were included in the final analyses. The estimated prevalence of HAND, ANI, MND and HAD were 44.9% (95% CI 37.4-52.7%), 26.2% (95% CI 20.7-32.7%), 8.5% (95% CI 5.6-12.7%), 2.1% (95% CI 1.2-3.7%), respectively. Factors associated with HAND were percent female, current CD4 count, education level and country development level (all ps < 0.05). Conclusion: Longitudinal cohort and multimodal neuroimaging studies are needed to verify the clinical prognosis and the underlying neurocognitive mechanism of HAND. In addition, it is urgently necessary to establish a standardized HAND diagnostic process.

The age-related trajectory of visual attention neural function is altered in adults living with HIV: A cross-sectional MEG study

Background

Despite living a normal lifespan, at least 35% of persons with HIV (PWH) in resource-rich countries develop HIV-associated neurocognitive disorder (HAND). This high prevalence of cognitive decline may reflect accelerated ageing in PWH, but the evidence supporting an altered ageing phenotype in PWH has been mixed.

Methods

We examined the impact of ageing on the orienting of visual attention in PWH using dynamic functional mapping with magnetoencephalography (MEG) in 173 participants age 22–72 years-old (94 uninfected controls, 51 cognitively-unimpaired PWH, and 28 with HAND). All MEG data were imaged using a state-of-the-art beamforming approach and neural oscillatory responses during attentional orienting were examined for ageing, HIV, and cognitive status effects.

Findings

All participants responded slower during trials that required attentional reorienting. Our functional mapping results revealed HIV-by-age interactions in left prefrontal theta activity, alpha oscillations in the left parietal, right cuneus, and right frontal eye-fields, and left dorsolateral prefrontal beta activity (p<.005). Critically, within PWH, we observed a cognitive status-by-age interaction, which revealed that ageing impacted the oscillatory gamma activity serving attentional reorienting differently in cognitively-normal PWH relative to those with HAND in the left temporoparietal, inferior frontal gyrus, and right prefrontal cortices (p<.005).

Interpretation

This study provides key evidence supporting altered ageing trajectories across vital attention circuitry in PWH, and further suggests that those with HAND exhibit unique age-related changes in the oscillatory dynamics serving attention function. Additionally, our neural findings suggest that age-related changes in PWH may serve a compensatory function.

Funding

National Institutes of Health, USA.

Prefrontal gating of sensory input differentiates cognitively impaired and unimpaired aging adults with HIV

Despite effective therapies that have extended the life expectancy of persons living with HIV, 35-70% of these adults still develop some form of cognitive impairment, and with a growing population of aging adults with HIV, the prevalence of these cognitive deficits is likely to increase. The mechanisms underlying these HIV-associated neurocognitive disorders remain poorly understood but are often accelerated by the aging process and accompanied by disturbances in sensory processing, which may contribute to the observed cognitive decline. The goal of the current study was to identify the impact of aging on HIV-related alterations in inhibitory processing and determine whether such alterations are related to cognitive impairment in neuroHIV. We used magnetoencephalographic imaging, advanced time series analysis methods, and a paired-pulse stimulation paradigm to interrogate inhibitory processing in 87 HIV-infected aging adults and 92 demographically matched uninfected controls (22-72 years old). Whole-brain maps linking age and neural indices were computed for each group and compared via Fisher's Z transformations. Peak voxel time-series data were also extracted from the resulting images to quantify the dynamics of spontaneous neural activity preceding stimulation onset in each group. Whole-brain analyses using the somatosensory gating index, a metric of inhibitory processing and age distinguished impaired adults with HIV from unimpaired HIV-infected adults and controls. Briefly, younger cognitively impaired adults with HIV strongly utilized the prefrontal cortices to gate somatosensory input, and the role of this region in gating was uniquely and significantly modulated by aging only in impaired adults with HIV. Spontaneous neural activity preceding stimulus onset was also significantly elevated in the prefrontal cortices of those with HIV-associated neurocognitive disorder, and this elevation was significantly related to the CD4 nadir across both HIV-infected groups. This is the first study to examine the impact of aging on inhibitory processing in HIV-infected adults with and without cognitive impairment. Our findings suggest that young adults with HIV-associated neurocognitive disorder utilize the prefrontal cortices to gate (i.e. suppress) redundant somatosensory input, and that this capacity uniquely diminishes with advancing age in impaired adults with HIV.

Methodological considerations for a better somatosensory gating paradigm: The impact of the inter-stimulus interval

Sensory gating (SG) is a neurophysiological phenomenon whereby the response to the second stimulus in a repetitive pair is attenuated. This filtering of irrelevant or redundant information is thought to preserve neural resources for more behaviorally-relevant stimuli and thereby reflect the functional inhibition of sensory input. Developing a SG paradigm in which optimal suppression of sensory input is achieved requires investigators to consider numerous parameters such as stimulus intensity, time between stimulus pairs, and the inter-stimulus interval (ISI) within each pair. While these factors have been well defined for the interrogation of auditory gating, the precise parameters for eliciting optimal gating in the somatosensory domain are far less understood. To address this, we investigated the impact of varying the ISI within each identical pair of stimuli on gating using magnetoencephalography (MEG). Specifically, 25 healthy young adults underwent paired-pulse electrical stimulation of the median nerve with increasing ISIs between 100 and 1000 ​ms (in 100 ​ms increments). Importantly, for correspondence with previous studies of somatosensory gating, both time-domain and oscillatory neural responses to somatosensory stimulation were evaluated. Our results indicated that gating of somatosensory input was optimal (i.e., best suppression) for trials with an ISI of 200-220 ​ms, as evidenced by the smallest gating ratios and through statistical modeling estimations of optimal suppression. Importantly, this was true irrespective of whether oscillatory or evoked neural activity was used to calculate SG. Interestingly, oscillatory metrics of gating calculated using peak gamma (30-75 ​Hz) power and frequency revealed more robust gating (i.e., smaller ratios) than those calculated using time-domain neural responses, suggesting that high frequency oscillations may provide a more sensitive measure of SG. These findings have important implications for the development of optimal protocols and analysis pipelines to interrogate SG and inhibitory processing with a higher degree of sensitivity and accuracy.

Brain structural correlates of trajectories to cognitive impairment in men with and without HIV disease

There are distinct trajectories to cognitive impairment among participants in the Multicenter AIDS Cohort Study (MACS). Here we analyzed the relationship between regional brain volumes and the individual trajectories to impairment in a subsample (n = 302) of the cohort. 302 (167 HIV-infected; mean age = 55.7 yrs.; mean education: 16.2 yrs.) of the men enrolled in the MACS MRI study contributed data to this analysis. We used voxel-based morphometry (VBM) to segment the brain images to analyze gray and white matter volume at the voxel-level. A Mixed Membership Trajectory Model had previously identified three distinct profiles, and each study participant had a membership weight for each of these three trajectories. We estimated VBM model parameters for 100 imputations, manually performed the post-hoc contrasts, and pooled the results. We examined the associations between brain volume at the voxel level and the MMTM membership weights for two profiles: one considered "unhealthy" and the other considered "Premature aging." The unhealthy profile was linked to the volume of the posterior cingulate gyrus/precuneus, the inferior frontal cortex, and the insula, whereas the premature aging profile was independently associated with the integrity of a portion of the precuneus. Trajectories to cognitive impairment are the result, in part, of atrophy in cortical regions linked to normal and pathological aging. These data suggest the possibility of predicting cognitive morbidity based on patterns of CNS atrophy.

Multi-spectral oscillatory dynamics serving directed and divided attention

Attention-related amplification of neural representations of external stimuli has been well documented in the visual domain, however, research concerning the oscillatory dynamics of such directed attention is relatively sparse in humans. Specifically, it is unknown which spectrally-specific neural responses are mainly impacted by the direction and division of attention, as well as whether the effects of attention on these oscillations are spatially disparate. In this study, we use magnetoencephalography and a visual-somatosensory oddball task to investigate the whole-brain oscillatory dynamics of directed (Experiment 1; N = 26) and divided (Experiment 2; N = 34) visual attention. Sensor-level data were transformed into the time-frequency domain and significant responses from baseline were imaged using a frequency-resolved beamformer. We found that multi-spectral cortical oscillations were stronger when attention was sustained in the visual space and that these effects exhibited informative spatial distributions that differed by frequency. More specifically, we found stronger frontal theta (4–8 Hz), frontal and occipital alpha (8–14 Hz), occipital beta (16–22 Hz), and frontal gamma (74–84 Hz) responses when visual attention was sustained than when it was directed away from the visual domain. Similarly, in the divided attention condition, we observed stronger fronto-parietal theta activity and temporo-parietal alpha and beta oscillations when visual attention was sustained toward the visual stimuli than divided between the visual and somatosensory domains. Investigating how attentional gain is implemented in the human brain is essential for better understanding how this process is degraded in disease, and may provide useful targets for future therapies.

Rhythmic Spontaneous Activity Mediates the Age-Related Decline in Somatosensory Function

Sensory gating is a neurophysiological process whereby the response to a second stimulus in a pair of identical stimuli is attenuated, and it is thought to reflect the capacity of the CNS to preserve neural resources for behaviorally relevant stimuli. Such gating is observed across multiple sensory modalities and is modulated by age, but the mechanisms involved are not understood. In this study, we examined somatosensory gating in 68 healthy adults using magnetoencephalography (MEG) and advanced oscillatory and time-domain analysis methods. MEG data underwent source reconstruction and peak voxel time series data were extracted to evaluate the dynamics of somatosensory gating, and the impact of spontaneous neural activity immediately preceding the stimulation. We found that gating declined with increasing age and that older adults had significantly reduced gating relative to younger adults, suggesting impaired local inhibitory function. Most importantly, older adults had significantly elevated spontaneous activity preceding the stimulation, and this effect fully mediated the impact of aging on sensory gating. In conclusion, gating in the somatosensory system declines with advancing age and this effect is directly tied to increased spontaneous neural activity in the primary somatosensory cortices, which is likely secondary to age-related declines in local GABA inhibitory function.

Interactive effects of HIV and ageing on neural oscillations: independence from neuropsychological performance

HIV infection is associated with increased age-related co-morbidities including cognitive deficits, leading to hypotheses of HIV-related premature or accelerated ageing. Impairments in selective attention and the underlying neural dynamics have been linked to HIV-associated neurocognitive disorder; however, the effect of ageing in this context is not yet understood. Thus, the current study aimed to identify the interactive effects of ageing and HIV on selective attention processing. A total of 165 participants (92 controls, 73 participants with HIV) performed a visual selective attention task while undergoing magnetoencephalography and were compared cross-sectionally. Spectrally specific oscillatory neural responses during task performance were imaged and linked with selective attention function. Reaction time on the task and regional neural activity were analysed with analysis of covariance (ANCOVA) models aimed at examining the age-by-HIV interaction term. Finally, these metrics were evaluated with respect to clinical measures such as global neuropsychological performance, duration of HIV infection and medication regimen. Reaction time analyses showed a significant HIV-by-age interaction, such that in controls older age was associated with greater susceptibility to attentional interference, while in participants with HIV, such susceptibility was uniformly high regardless of age. In regard to neural activity, theta-specific age-by-HIV interaction effects were found in the prefrontal and posterior parietal cortices. In participants with HIV, neuropsychological performance was associated with susceptibility to attentional interference, while time since HIV diagnosis was associated with parietal activity above and beyond global neuropsychological performance. Finally, current efavirenz therapy was also related to increased parietal interference activity. In conclusion, susceptibility to attentional interference in younger participants with HIV approximated that of older controls, suggesting evidence of HIV-related premature ageing. Neural activity serving attention processing indicated compensatory recruitment of posterior parietal cortex as participants with HIV infection age, which was related to the duration of HIV infection and was independent of neuropsychological performance, suggesting an altered trajectory of neural function.

Attention modulates the gating of primary somatosensory oscillations

Sensory gating (SG) is a well-studied phenomenon in which neural responses are reduced to identical stimuli presented in succession, and is thought to represent the functional inhibition of primary sensory information that is redundant in nature. SG is traditionally considered pre-attentive, but little is known about the effects of attentional state on this process. In this study, we investigate the impact of directed attention on somatosensory SG using magnetoencephalography. Healthy young adults (n ​= ​26) performed a novel somato-visual paired-pulse oddball paradigm, in which attention was directed towards or away from paired-pulse stimulation of the left median nerve. We observed a robust evoked (i.e., phase-locked) somatosensory response in the time domain, and three stereotyped oscillatory responses in the time-frequency domain including an early theta response (4-8 ​Hz), and later alpha (8-14 ​Hz) and beta (20-26 ​Hz) responses across attentional states. The amplitudes of the evoked response and the theta and beta oscillations were gated for the second stimulus, however, only the gating of the oscillatory responses was altered by attention. Specifically, directing attention to the somatosensory domain enhanced SG of the early theta response, while reducing SG of the later alpha and beta responses. Further, prefrontal alpha-band coherence with the primary somatosensory cortex was greater when attention was directed towards the somatosensory domain, supporting a frontal modulatory effect on the alpha response in primary somatosensory regions. These findings highlight the dynamic effects of attentional modulation on somatosensory processing, and the importance of considering attentional state in studies of SG.

Opioid and chemokine regulation of cortical synaptodendritic damage in HIV-associated neurocognitive disorders

Human immunodeficiency virus (HIV)-associated neurocognitive disorders (HAND) persist despite effective antiretroviral therapies (ART). Evidence suggests that modern HAND is driven by subtle synaptodendritic damage in select brain regions, as ART-treated patients do not display overt neuronal death in postmortem brain studies. HAND symptoms are also aggravated by drug abuse, particularly with injection opioids. Opioid use produces region-specific synaptodendritic damage in similar brain regions, suggesting a convergent mechanism that may enhance HAND progression in opioid-using patients. Importantly, studies indicate that synaptodendritic damage and cognitive impairment in HAND may be reversible. Activation of the homeostatic chemokine receptor CXCR4 by its natural ligand CXCL12 positively regulates neuronal survival and dendritic spine density in cortical neurons, reducing functional deficits. However, the molecular mechanisms that underlie CXCR4, as well as opioid-mediated regulation of dendritic spines are not completely defined. Here, we will consolidate studies that describe the region-specific synaptodendritic damage in the cerebral cortex of patients and animal models of HAND, describe the pathways by which opioids may contribute to cortical synaptodendritic damage, and discuss the prospects of using the CXCR4 signaling pathway to identify new approaches to reverse dendritic spine deficits. Additionally, we will discuss novel research questions that have emerged from recent studies of CXCR4 and µ-opioid actions in the cortex. Understanding the pathways that underlie synaptodendritic damage and rescue are necessary for developing novel, effective therapeutics for this growing patient population.

No Evidence for Accelerated Aging-Related Brain Pathology in Treated Human Immunodeficiency Virus: Longitudinal Neuroimaging Results From the Comorbidity in Relation to AIDS (COBRA) Project

Background

Despite successful antiretroviral therapy, people living with human immunodeficiency virus (PLWH) experience higher rates of age-related morbidity, including abnormal brain structure, brain function, and cognitive impairment. This has raised concerns that PLWH may experience accelerated aging-related brain pathology.

Methods

We performed a multicenter longitudinal study of 134 virologically suppressed PLWH (median age, 56.0 years) and 79 demographically similar human immunodeficiency virus (HIV)-negative controls (median age, 57.2 years). To measure cognitive performance and brain pathology, we conducted detailed neuropsychological assessments and multimodality neuroimaging (T1-weighted, T2-weighted, diffusion magnetic resonance imaging [MRI], resting-state functional MRI, spectroscopy, arterial spin labeling) at baseline and at 2 years. Group differences in rates of change were assessed using linear mixed effects models.

Results

One hundred twenty-three PLWH and 78 HIV-negative controls completed longitudinal assessments (median interval, 1.97 years). There were no differences between PLWH and HIV-negative controls in age, sex, years of education, smoking or alcohol use. At baseline, PLWH had poorer global cognitive performance (P < .01), lower gray matter volume (P = .04), higher white matter hyperintensity load (P = .02), abnormal white matter microstructure (P < .005), and greater brain-predicted age difference (P = .01). Longitudinally, there were no significant differences in rates of change in any neuroimaging measure between PLWH and HIV-negative controls (P > .1). Cognitive performance was longitudinally stable in both groups.

Conclusions

We found no evidence that middle-aged PLWH, when receiving successful treatment, are at increased risk of accelerated aging-related brain changes or cognitive decline over 2 years.

Aberrant occipital dynamics differentiate HIV-infected patients with and without cognitive impairment

Combination antiretroviral therapies have revolutionized the treatment of HIV infection, and many patients now enjoy a lifespan equal to that of the general population. However, HIV-associated neurocognitive disorders (HAND) remain a major health concern, with between 30% and 70% of all HIV-infected patients developing cognitive impairments during their life time. One important feature of HAND is visuo-perceptual deficits, but the systems-level neural dynamics underlying these impairments are poorly understood. In the current study, we use magnetoencephalography and advanced time series analyses to examine these neural dynamics during a visuospatial processing task in a group of HIV-infected patients without HAND (n = 25), patients with HAND (n = 18), and a group of demographically-matched uninfected controls (n = 24). All participants completed a thorough neuropsychological assessment, and underwent magnetoencephalography and structural MRI protocols. In agreement with previous studies, patients with HAND performed significantly worse than HIV-infected patients without HAND and controls on the cognitive task, in terms of increased reaction time and decreased accuracy. Our magnetoencephalography results demonstrated that both spontaneous and neural oscillatory activity within the occipital cortices were affected by HIV infection, and that these patterns predicted behavioural performance (i.e. accuracy) on the task. Specifically, spontaneous neural activity in the alpha (8–16 Hz) and gamma (52–70 Hz) bands during the prestimulus baseline period, as well as oscillatory theta responses (4–8 Hz) during task performance were aberrant in HIV-infected patients, with both spontaneous alpha and oscillatory theta activity significantly predicting accuracy on the task and neuropsychological performance outside of the magnetoencephalography scanner. Importantly, these rhythmic patterns of population-level neural activity also distinguished patients by HAND status, such that spontaneous alpha activity in patients with HAND was elevated relative to HIV-infected patients without HAND and controls. In contrast, HIV-infected patients with and without HAND had increased spontaneous gamma compared to controls. Finally, there was a stepwise decrease in oscillatory theta activity as a function of disease severity, such that the response diminished from controls to patients without HAND to patients with HAND. Interestingly, the strength of the relationship between this theta response and accuracy also dissociated patient groups in a similar manner (controls > HIV with no HAND > HIV with HAND), indicating a reduced coupling between neurophysiology and behaviour in HIV-infected patients. This study provides the first neuroimaging evidence of a dissociation between HIV-infected patients with and without HAND, and these findings shed new light on the neural bases of cognitive impairment in HIV infection.

Aberrant brain dynamics in neuroHIV: Evidence from magnetoencephalographic (MEG) imaging

Magnetoencephalography (MEG) is a noninvasive, silent, and totally passive neurophysiological imaging method with excellent temporal resolution (~1ms) and good spatial precision (~3-5mm). While MEG studies of neuroHIV remain relatively rare, the number of studies per year has sharply increased recently and this trend will likely continue into the foreseeable future. The current in-depth review focuses on the studies that have been conducted to date, which include investigations of somatosensory and visual modalities, resting-state, as well as motor control and higher-level functions such as working memory and visual attention. The review begins with an introduction to the principles and methods of MEG, and then transitions to a review of each of the empirical studies that have been conducted to date, separated by sensory modality for the basic studies and cognitive domain for the higher-level investigations. As such, this review attempts to be exhaustive in its coverage of empirical MEG studies of neuroHIV. Across studies major themes emerge including aberrant neural oscillatory activity in HIV-infected adults, both in primary sensory regions of the brain and higher-order executive regions. Many studies have also connected the amplitude of neural oscillations to behavioral and/or neuropsychological function in the study population, making a vital connection to performance and improving the veracity of the findings. One conspicuous emerging area is the use of MEG to distinguish cognitively-impaired from unimpaired HIV-infected adults, with major success reported and future studies sure to come. The review concludes with a summary of findings and suggested focus areas for future studies.

Visual evoked and event-related brain potentials in HIV-infected adults: a longitudinal study over 2.5 years

PURPOSE

The aim of this neurophysiological study was to monitor changes in the visual and cognitive function of HIV-infected patients treated with combination antiretroviral therapy.

METHODS

Eleven adult Czech HIV+ patients, with a mean age of 35 years and CD4 cell count ≥ 230 × 10⁶ cells/L of blood at the time of enrollment, underwent four to six examinations over the course of 2.5 years to evaluate pattern-reversal and motion-onset visual evoked potentials (P-VEPs and M-VEPs), visually driven oddball event-related potentials (ERPs) and Montreal Cognitive Assessments. In addition to evaluating the intraindividual change in the observed parameters, we also compared patient data to data from eleven age- and gender-matched controls.

RESULTS

We did not find any significant differences in P-VEPs between the patients and controls or in the paired comparison of the first and last visit. The only significant finding for P-VEPs was a linear trend in prolongation of the 20' P-VEP P100 peak time. In M-VEPs, we found a significant intergroup difference in the N160 peak time recorded during the first visit for peripheral M-VEPs only. During the last visit, all N160 peak times for patients differed significantly from those of the control group. The only intervisit difference close to the level of significance was for peripheral M-VEPs, which confirmed the trend analysis. No significant differences between patients and controls were found in the ERPs, but the P300 peak time showed a significant difference between the first and last visits, as confirmed by the trend. Patient reaction time was not significantly delayed at the first visit; however, it was prolonged with time, as confirmed by the trend.

CONCLUSION

Our aim was to evaluate whether antiretroviral treatment in HIV+ patients is sufficient to preserve brain visual function. The optic nerve and primary visual cortex function tested by the P-VEPs seem to be preserved. The prolongation of the M-VEPs suggests an individually detectable decline in CNS function, but these changes did not show a progression during the follow-up. From a longitudinal perspective, the trends in peak time prolongation of the 20' P-VEP, peripheral M-VEP, ERP and reaction time suggest a faster decline than that caused by aging in healthy populations, as previously described in a cross-sectional study.

Different roles of frontal versus striatal atrophy in HIV-associated neurocognitive disorders

Gray matter (GM) atrophy is frequently detected in persons living with HIV, even in the era of combination antiretroviral therapy (cART), but the specificity of regions affected remains elusive. For instance, which regions are consistently affected in HIV? In addition, atrophy at which regions is frequently associated with neurocognitive impairment in HIV? Resolving these questions can potentially help to establish the possible neural profiles of HIV-associated neurocognitive disorders (HAND) severity, which currently is solely defined by neurobehavioral assessments. Here, we addressed these questions using a novel meta-analysis technique, the colocalization-likelihood estimation (CLE) technique, to quantitatively synthesize the findings of GM atrophy in HIV+ adults. Twenty-one of 386 studies published between 1988 and November 2017 and identified in PubMed were selected, plus four identified in other resources. In the end, 25 studies (1,370 HIV+ adults, 889 HIV- controls) were included in the meta-analysis. This technique revealed that GM atrophy in HIV+ adults was dominated by two distinct but nonexclusive profiles: frontal (including anterior cingulate cortex, [ACC]) atrophy, which was associated withHIV-disease and consistently differentiated HIV+ adults from HIV- controls; and caudate/striatum atrophy, which was associated with neurocognitive impairment. The critical role of caudate/striatum atrophy in neurocognitive impairment was further supported by a separate data analysis, which examined the findings of correlation analyses between GM and neurocognitive performance. These results suggest that the frontal lobe and the striatum play critical but differential roles in HAND. A neural model of HAND severity was proposed with several testable predictions.

Chained regularization for identifying brain patterns specific to HIV infection

Human Immunodeficiency Virus (HIV) infection continues to have major adverse public health and clinical consequences despite the effectiveness of combination Antiretroviral Therapy (cART) in reducing HIV viral load and improving immune function. As successfully treated individuals with HIV infection age, their cognition declines faster than reported for normal aging. This phenomenon underlines the importance of improving long-term care, which requires a better understanding of the impact of HIV on the brain. In this paper, automated identification of patients and brain regions affected by HIV infection are modeled as a classification problem, whose solution is determined in two steps within our proposed Chained-Regularization framework. The first step focuses on selecting the HIV pattern (i.e., the most informative constellation of brain region measurements for distinguishing HIV infected subjects from healthy controls) by constraining the search for the optimal parameter setting of the classifier via group sparsity (ℓ2,1-norm). The second step improves classification accuracy by constraining the parameterization with respect to the selected measurements and the Euclidean regularization (ℓ2-norm). When applied to the cortical and subcortical structural Magnetic Resonance Images (MRI) measurements of 65 controls and 65 HIV infected individuals, this approach is more accurate in distinguishing the two cohorts than more common models. Finally, the brain regions of the identified HIV pattern concur with the HIV literature that uses traditional group analysis models.

Altered intrinsic local activity and cognitive dysfunction in HIV patients: A resting-state fMRI study

Purpose

To characterize resting-state brain activation patterns and investigate altered areas for cognitive decline in HIV patients.

Methods

Twelve male HIV patients with intact cognition (HIV-IC), 10 with HIV-associated neurocognitive disorder (HAND), and 11 male healthy controls (HC) underwent resting-state functional MRI (rsfMRI). Three rsfMRI values, regional homogeneity (ReHo), amplitude of low-frequency fluctuation (ALFF), and fractional ALFF (fALFF) were calculated and compared between groups. Correlation analyses were performed between rsfMRI values and neuropsychological tests.

Results

rsfMRI analyses revealed decreased rsfMRI values in the frontal areas, and increases in the posterior brain regions for both HIV-IC and HAND compared to HC. When directly compared to HIV-IC, HAND showed lower fALFF in the orbitofrontal cortex and higher ReHo in the primary sensorimotor area. Additionally, decreased orbitofrontal fALFF, increased sensorimotor ReHo, and a larger difference between the two values were highly correlated with decreased verbal memory and executive function in HIV patients.

Conclusions

Regardless of cognitive status, altered local intrinsic activities were found in HIV patients. The orbitofrontal cortex and primary sensorimotor area were more disrupted in HAND relative to HIV-IC and correlated with behavioral performance, suggesting these areas are relevant to cognitive impairment in HIV patients.

Changes in resting-state functional brain activity are associated with waning cognitive functions in HIV-infected children

Delayed brain development in perinatally HIV-infected children may affect the functional brain activity and subsequently cognitive function. The current study evaluated the functional brain activity in HIV-infected children by quantifying the amplitude of low frequency fluctuations (ALFF) and functional connectivity (FC). Additionally, correlation of ALFF and FC with cognitive measures was performed. Twenty-six HIV-infected children and 20 control children underwent neuropsychological (NP) assessment and resting-state functional magnetic resonance imaging (rs-fMRI). ALFF and FC maps were generated and group differences were analyzed using two-sample t-test. Furthermore, ALFF and FC showing significant group differences were correlated with NP scores using Pearson's correlation. Significantly lower ALFF in the left middle temporal gyrus, precentral and post central gyrus was observed in HIV-infected children compared to controls. FC was significantly reduced in the right inferior parietal, vermis, middle temporal and left postcentral regions, and significantly increased in the right precuneus, superior parietal and left middle frontal regions in HIV-infected children as compared to control. HIV-infected children showed significantly lower NP scores in various domains including closure, exclusion, memory, verbal meaning, quantity and hidden figure than controls. These waning cognitive functions were significantly associated with changes in ALFF and FC in HIV-infected children. The findings suggest that abnormal ALFF and FC may responsible for cognitive deficits in HIV-infected children. ALFF and FC in association with cognitive evaluation may provide a clinical biomarker to evaluate functional brain activity and to plan neurocognitive intervention in HIV-infected children undergoing standard treatment.

Neural dynamics of selective attention deficits in HIV-associated neurocognitive disorder

Objective

To identify the neural markers of attention dysfunction in patients with HIV-associated neurocognitive disorder (HAND).

Methods

Sixty participants, including 40 HIV-infected adults (half with HAND) and 20 demographically matched controls performed a visual selective attention task while undergoing high-density magnetoencephalography. Neuronal activity related to selective attention processing was quantified and compared across the 3 groups, and correlated with neuropsychological measures of attention and executive function. Spontaneous neural activity was also extracted from these attention-related cortical areas and examined with respect to HAND status.

Results

HIV-infected participants with and without HAND exhibited behavioral selective attention deficits on the magnetoencephalography task, as indicated by an increased flanker effect. Neuronal measures of flanker interference activity in the alpha and theta range revealed differential dynamics in attention-related brain areas across the 3 groups, especially in those with HAND. In addition, theta range flanker interference activity in the left inferior frontal and dorsolateral prefrontal cortex was associated with executive function and attention composite scores, respectively. Progressively stronger spontaneous alpha and theta activity was also found in unimpaired HIV-infected and HAND participants relative to controls across brain regions implicated in different components of attention processing.

Conclusions

Behavioral and neuronal metrics of selective attention performance distinguish participants with HAND from controls and unimpaired HIV-infected participants. These metrics, along with measures of local spontaneous neural activity, may hold promise as early markers of cognitive decline in participants with HIV infection and be useful prognostic indicators for HAND.

Structural and functional brain imaging in acute HIV

Background

HIV RNA is identified in cerebrospinal fluid (CSF) within eight days of estimated viral exposure. Neurological findings and impaired neuropsychological testing performance are documented in a subset of individuals with acute HIV infection (AHI). The purpose of this study was to determine whether microstructural white matter and resting-state functional connectivity (rsFC) are disrupted in AHI.

Methods

We examined 49 AHI (100% male; mean age = 30 ± SD 9.9) and 23 HIV-uninfected Thai participants (78% male; age = 30 ± 5.5) with diffusion tensor imaging (DTI) and rsFC acquired at 3 Tesla, and four neuropsychological tests (summarized as NPZ-4). MRI for the AHI group was performed prior to combination antiretroviral treatment (ART) in 26 participants and on average two days (range:1–5) after ART in 23 participants. Fractional anisotropy (FA), mean (MD), axial (AD), and radial diffusivity (RD) were quantified for DTI. Seed-based voxelwise rsFC analyses were completed for the default mode (DMN), fronto-parietal, and salience and 6 subcortical networks. rsFC and DTI analyses were corrected for family-wise error, with voxelwise comparisons completed using t-tests. Group-specific voxelwise regressions were conducted to examine relationships between imaging indices, HIV disease variables, and treatment status.

Results

The AHI group had a mean (SD) CD4 count of 421(234) cells/mm³ plasma HIV RNA of 6.07(1.1) log₁₀ copies/mL and estimated duration of infection of 20(5.5) days. Differences between AHI and CO groups did not meet statistical significance for DTI metrics. Within the AHI group, voxelwise analyses revealed associations between brief exposure to ART and higher FA and lower RD and MD bilaterally in the corpus callosum, corona radiata, and superior longitudinal fasciculus (p < 0.05). Diffusion indices were unrelated to clinical variables or NPZ-4. The AHI group had reduced rsFC between left parahippocampal cortex (PHC) of the DMN and left middle frontal gyrus compared to CO (p < 0.002). Within AHI, ART status was unrelated to rsFC. However, higher CD4 cell count associated with increased rsFC for the right lateral parietal and PHC seeds in the DMN. Direct associations were noted between NPZ-4 correspond to higher rsFC of the bilateral caudate seed (p < 0.002).

Conclusions

Study findings reveal minimal disruption to structural and functional brain integrity in the earliest stages of HIV. Longitudinal studies are needed to determine if treatment with ART initiated in AHI is sufficient to prevent the evolution of brain dysfunction identified in chronically infected individuals.

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DTI indicates no significant differences between acute HIV and uninfected controls.

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rsfMRI reflects limited reduced rsFC in acute HIV compared to uninfected controls.

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Relatively preserved brain integrity identified in acute HIV vs uninfected controls.

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Cognitive testing and CD4 lymphocyte counts associate with rsFC activity in acute HIV.

Aberrant oscillatory dynamics during somatosensory processing in HIV-infected adults

While the arrival of combination antiretroviral therapy significantly decreased the prevalence of HIV-associated dementia, between 35 and 70% of all infected adults continue to develop some form of cognitive impairment. These deficits appears to affect multiple neural subsystems, but the mechanisms and extent of damage are not fully understood. In the current study, we utilized magnetoencephalography (MEG), advanced oscillatory analysis methods, and a paired-pulse somatosensory stimulation paradigm to interrogate pre-attentive inhibitory processing in 43 HIV-infected adults and 28 demographically-matched uninfected controls. MEG responses were imaged using a beamformer, and time series data were extracted from the peak voxel in grand-averaged functional brain images to quantify the dynamics of sensory gating, oscillatory power, spontaneous power, and other neural indices. We found a significantly weakened response to the second stimulation compared to the first across groups, indicating significant sensory gating irrespective of HIV-infection. Interestingly, HIV-infected participants exhibited reduced neural responses in the 20-75 Hz gamma range to each somatosensory stimulation compared to uninfected controls, and exhibited significant alterations in peak gamma frequency in response to the second stimulation. Finally, HIV-infected participants also had significantly stronger spontaneous activity in the gamma range (i.e., 20-75 Hz) during the baseline period before stimulation onset. In conclusion, while HIV-infected participants had the capacity to efficiently gate somatosensory input, their overall oscillatory responses were weaker, spontaneous baseline activity was stronger, and their response to the second stimulation had an altered peak gamma frequency. We propose that this pattern of deficits suggests dysfunction in the somatosensory cortices, which is potentially secondary to accelerated aging.

Accelerated and Premature Aging Characterizing Regional Cortical Volume Loss in Human Immunodeficiency Virus Infection: Contributions From Alcohol, Substance Use, and Hepatitis C Coinfection

BACKGROUND

Life expectancy of successfully treated human immunodeficiency virus (HIV)-infected individuals is approaching normal longevity. The growing HIV population ≥50 years of age is now at risk of developing HIV-associated neurocognitive disorder, acquiring coinfection with the hepatitis C virus (HCV), and engaging in hazardous drinking or drug consumption that can adversely affect trajectories of the healthy aging of brain structures.

METHODS

This cross-sectional/longitudinal study quantified regional brain volumes from 1101 magnetic resonance imaging scans collected over 14 years in 549 participants (25 to 75 years of age): 68 HIV-infected individuals without alcohol dependence, 60 HIV-infected individuals with alcohol dependence, 222 alcohol-dependent individuals, and 199 control subjects. We tested 1) whether localized brain regions in HIV-infected individuals exhibited accelerated aging, or alternatively, nonaccelerated premature aging deficits; and 2) the extent to which alcohol or substance dependence or HCV coinfection altered brain aging trajectories.

RESULTS

The HIV-infected cohort exhibited steeper declining volume trajectories than control subjects, consistently in the frontal cortex. Nonaccelerated volume deficits occurred in the temporal, parietal, insular, and cingulate regions of all three diagnostic groups. Alcohol and drug dependence comorbidities and HCV coinfection exacerbated HIV-related volume deficits. Accelerated age interactions in frontal and posterior parietal volumes endured in HIV-infected individuals free of alcohol or substance dependence and HCV infection comorbidities. Functionally, poorer HIV-associated neurocognitive disorder scores and Veterans Aging Cohort Study indices correlated with smaller regional brain volumes in the HIV-infected individuals without alcohol dependence and alcohol-dependent groups.

CONCLUSIONS

HIV infection itself may confer a heightened risk of accelerated brain aging, potentially exacerbated by HCV coinfection and substance dependency. Confirmation would require a prospective study with a preinfection baseline.

Structural Covariance of Gray Matter Volume in HIV Vertically Infected Adolescents

Human immunodeficiency virus (HIV) infection significantly affect neurodevelopmental and behavioral outcomes. We investigated whether alterations of gray matter organization and structural covariance networks with vertical HIV infection adolescents exist, by using the GAT toolbox. MRI data were analysed from 25 HIV vertically infected adolescents and 33 HIV-exposed-uninfected control participants. The gray matter volume (GMV) was calculated, and structural brain networks were reconstructed from gray matter co-variance. Gray matter losses were pronounced in anterior cingulate cortex (ACC), right pallidum, right occipital lobe, inferior parietal lobe, and bilateral cerebellum crus. The global brain network measures were not significantly different between the groups; however, the nodal alterations were most pronounced in frontal, temporal, basal ganglia, cerebellum, and temporal lobes. Brain hubs in the HIV-infected subjects increased in number and tended to shift to sensorimotor and temporal areas. In the HIV-infected subjects, decreased GMVs in ACC and bilateral cerebellum were related to lower Mini-Mental State Examination scores; the CD4 counts were positively related to the GMVs in ACC and sensorimotor areas. These findings suggest that focally reduced gray matter, disrupted nodal profiles of structural wirings, and a shift in hub distribution may represent neuroanatomical biomarkers of HIV infection on the developing brain.

Imaging studies of the HIV-infected brain

Human immunodeficiency virus (HIV) enters the brain early after infecting humans and may remain in the central nervous system despite successful antiretroviral treatment. Many neuroimaging techniques were used to study HIV+ patients with or without opportunistic infections. These techniques assessed abnormalities in brain structures (using computed tomography, structural magnetic resonance imaging (MRI), diffusion MRI) and function (using functional MRI at rest or during a task, and perfusion MRI with or without a contrast agent). In addition, single-photon emission computed tomography with various tracers (e.g., thallium-201, Tc99-HMPAO) and positron emission tomography with various agents (e.g., [18F]-dexoyglucose, [11C]-PiB, and [11C]-TSPO tracers), were applied to study opportunistic infections or HIV-associated neurocognitive disorders. Neuroimaging provides diagnoses and biomarkers to quantitate the severity of brain injury or to monitor treatment effects, and may yield insights into the pathophysiology of HIV infection. As the majority of antiretroviral-stable HIV+ patients are living longer, age-related comorbid disorders (e.g., additional neuroinflammation, cerebrovascular disorders, or other dementias) will need to be considered. Other highly prevalent conditions, such as substance use disorders, psychiatric illnesses, and the long-term effects of combined antiretroviral therapy, all may lead to additional brain injury. Neuroimaging studies could provide knowledge regarding how these comorbid conditions impact the HIV-infected brain. Lastly, specific molecular imaging agents may be needed to assess the central nervous system viral reservoir.

Alteration of brain network topology in HIV-associated neurocognitive disorder: A novel functional connectivity perspective

HIV is capable of invading the brain soon after seroconversion. This ultimately can lead to deficits in multiple cognitive domains commonly referred to as HIV-associated neurocognitive disorders (HAND). Clinical diagnosis of such deficits requires detailed neuropsychological assessment but clinical signs may be difficult to detect during asymptomatic injury of the central nervous system (CNS). Therefore neuroimaging biomarkers are of particular interest in HAND. In this study, we constructed brain connectivity profiles of 40 subjects (20 HIV positive subjects and 20 age-matched seronegative controls) using two different methods: a non-linear mutual connectivity analysis approach and a conventional method based on Pearson's correlation. These profiles were then summarized using graph-theoretic methods characterizing their topological network properties. Standard clinical and laboratory assessments were performed and a battery of neuropsychological (NP) tests was administered for all participating subjects. Based on NP testing, 14 of the seropositive subjects exhibited mild neurologic impairment. Subsequently, we analyzed associations between the network derived measures and neuropsychological assessment scores as well as common clinical laboratory plasma markers (CD4 cell count, HIV RNA) after adjusting for age and gender. Mutual connectivity analysis derived graph-theoretic measures, Modularity and Small Worldness, were significantly (p < 0.05, FDR adjusted) associated with the Executive as well as Overall z-score of NP performance. In contrast, network measures derived from conventional correlation-based connectivity did not yield any significant results. Thus, changes in connectivity can be captured using advanced time-series analysis techniques. The demonstrated associations between imaging-derived graph-theoretic properties of brain networks with neuropsychological performance, provides opportunities to further investigate the evolution of HAND in larger, longitudinal studies. Our analysis approach, involving non-linear time-series analysis in conjunction with graph theory, is promising and it may prove to be useful not only in HAND but also in other neurodegenerative disorders.

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Currently, cognitive impairment in HIV positive individuals is detected using detailed neuropsychological testing.

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Analysis of fMRI data using MCA-GRBF method revealed significant associations with current clinical standards.

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In contrast, functional connectivity analysis using conventional correlation analysis does not produce any such associations.

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Nonlinear analysis using MCA-GRBF method can potentially capture relevant information when compared to conventional methods.

Motor-related brain abnormalities in HIV-infected patients: a multimodal MRI study

PURPOSE

It is generally believed that HIV infection could cause HIV-associated neurocognitive disorders (HAND) across a broad range of functional domains. Some of the most common findings are deficits in motor control. However, to date no neuroimaging studies have evaluated basic motor control in HIV-infected patients using a multimodal approach.

METHODS

In this study, we utilized high-resolution structural imaging and task-state functional magnetic resonance imaging (fMRI) to assess brain structure and motor function in a homogeneous cohort of HIV-infected patients.

RESULTS

We found that HIV-infected patients had significantly reduced gray matter (GM) volume in cortical regions, which are involved in motor control, including the bilateral posterior insula cortex, premotor cortex, and supramarginal gyrus. Increased activation in bilateral posterior insula cortices was also demonstrated by patients during hand movement tasks compared with healthy controls. More importantly, the reduced GM in bilateral posterior insula cortices was spatially coincident with abnormal brain activation in HIV-infected patients. In addition, the results of partial correlation analysis indicated that GM reduction in bilateral posterior insula cortices and premotor cortices was significantly correlated with immune system deterioration.

CONCLUSION

This study is the first to demonstrate spatially coincident GM reduction and abnormal activation during motor performance in HIV-infected patients. Although it remains unknown whether the brain deficits can be recovered, our findings may yield new insights into neurologic injury underlying motor dysfunction in HAND.

Veterans with post-traumatic stress disorder exhibit altered emotional processing and attentional control during an emotional Stroop task

BACKGROUND

Post-traumatic stress disorder (PTSD) is often associated with attention allocation and emotional regulation difficulties, but the brain dynamics underlying these deficits are unknown. The emotional Stroop task (EST) is an ideal means to monitor these difficulties, because participants are asked to attend to non-emotional aspects of the stimuli. In this study, we used magnetoencephalography (MEG) and the EST to monitor attention allocation and emotional regulation during the processing of emotionally charged stimuli in combat veterans with and without PTSD.

METHOD

A total of 31 veterans with PTSD and 20 without PTSD performed the EST during MEG. Three categories of stimuli were used, including combat-related, generally threatening and neutral words. MEG data were imaged in the time-frequency domain and the network dynamics were probed for differences in processing threatening and non-threatening words.

RESULTS

Behaviorally, veterans with PTSD were significantly slower in responding to combat-related relative to neutral and generally threatening words. Veterans without PTSD exhibited no significant differences in responding to the three different word types. Neurophysiologically, we found a significant three-way interaction between group, word type and time period across multiple brain regions. Follow-up testing indicated stronger theta-frequency (4-8 Hz) responses in the right ventral prefrontal (0.4-0.8 s) and superior temporal cortices (0.6-0.8 s) of veterans without PTSD compared with those with PTSD during the processing of combat-related words.

CONCLUSIONS

Our data indicated that veterans with PTSD exhibited deficits in attention allocation and emotional regulation when processing trauma cues, while those without PTSD were able to regulate emotion by directing attention away from threat.

Children with cerebral palsy have altered oscillatory activity in the motor and visual cortices during a knee motor task

The neuroimaging literature on cerebral palsy (CP) has predominantly focused on identifying structural aberrations within the white matter (e.g., fiber track integrity), with very few studies examining neural activity within the key networks that serve the production of motor actions. The current investigation used high-density magnetoencephalography to begin to fill this knowledge gap by quantifying the temporal dynamics of the alpha and beta cortical oscillations in children with CP (age = 15.5 ± 3 years; GMFCS levels II–III) and typically developing (TD) children (age = 14.1 ± 3 years) during a goal-directed isometric target-matching task using the knee joint. Advanced beamforming methods were used to image the cortical oscillations during the movement planning and execution stages. Compared with the TD children, our results showed that the children with CP had stronger alpha and beta event-related desynchronization (ERD) within the primary motor cortices, premotor area, inferior parietal lobule, and inferior frontal gyrus during the motor planning stage. Differences in beta ERD amplitude extended through the motor execution stage within the supplementary motor area and premotor cortices, and a stronger alpha ERD was detected in the anterior cingulate. Interestingly, our results also indicated that alpha and beta oscillations were weaker in the children with CP within the occipital cortices and visual MT area during movement execution. These altered alpha and beta oscillations were accompanied by slower reaction times and substantial target matching errors in the children with CP. We also identified that the strength of the alpha and beta ERDs during the motor planning and execution stages were correlated with the motor performance. Lastly, our regression analyses suggested that the beta ERD within visual areas during motor execution primarily predicted the amount of motor errors. Overall, these data suggest that uncharacteristic alpha and beta oscillations within visuomotor cortical networks play a prominent role in the atypical motor actions exhibited by children with CP.

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Children with CP performed an isometric task with the knee joint.

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Children with CP had stronger alpha and beta ERD during motor planning.

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These ERD differences extended through the motor execution period.

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Occipital cortices and visual MT area alpha and beta ERD were weaker.

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Altered alpha and beta ERD were accompanied by impaired motor actions.

The electrophysiology of neuroHIV: A systematic review of EEG and MEG studies in people with HIV infection since the advent of highly-active antiretroviral therapy

OBJECTIVE

The Human Immunodeficiency Virus (HIV) has an impact on the brain, even when the infection is well-controlled with modern highly-active antiretroviral therapy (HAART). While dementia is rare in those on HAART, milder cognitive impairment is common. The causes, patterns, and evolution of brain dysfunction in people living with HIV remain uncertain. We evaluate whether electrophysiological methods provide informative measures of brain dysfunction in this population.

METHODS

A systematic literature search identified studies that used EEG or MEG to evaluate persons living with HIV published between 1996 (when HAART became available) and 2016.

RESULTS

Twenty-eight studies were identified. Most involved small samples, and all but four were cross-sectional. Reduced amplitude of Event Related Potentials and decreased power in the alpha band at rest were the most frequent differences between people with and without HIV infection. Of the 16 studies that also assessed cognitive ability, 13 found a significant relationship between cognition and electrophysiological changes in the HIV+ groups. Five of those studies also reported a significant relationship with current immunosuppression, suggesting a direct effect of HIV on the brain. There were few longitudinal studies; whether these electrophysiological changes progress over time, or respond to treatment, remains unclear.

CONCLUSIONS

EEG and MEG can provide useful information about brain dysfunction in people with HIV infection, but more consistent assessments of both cognition and EEG patterns, as well as longitudinal studies with larger, better characterized samples are needed.

SIGNIFICANCE

This is the first systematic review of electrophysiological findings in HIV since the availability of HAART. EEG and MEG measures are sensitive to brain dysfunction in this population, and could complement other approaches in improving the assessment, understanding and treatment of neurocognitive disorders in HIV.

The cortical signature of symptom laterality in Parkinson's disease

Patients with Parkinson's disease (PD) often present with unilateral motor symptoms that eventually spread to the other side. This symptom lateralization is diagnostically important, as it serves to distinguish PD from other motor disorders with overlapping symptom profiles. Further, recent studies have shown that the side of symptom onset is important for prognosis, as there are differences in the rate of disease progression and the incidence of secondary symptoms between right- and left-dominant (RD, LD) patients. Physiologically, previous studies have shown asymmetrical decline in structure and metabolism throughout the basal ganglia, although connecting this directly to motor function has been difficult. To identify the neurophysiological basis of symptom laterality in PD, we recorded magnetoencephalography (MEG) during left- and right-hand movement paradigms in patients with PD who exhibited either RD or LD symptomatology. The beta oscillations serving these movements were then imaged using beamforming methods, and we extracted the time series of the peak voxel in the left and right primary motor cortices for each movement. In addition, each patient's symptom asymmetry was quantitated using the Unified Parkinson's Disease Rating Scale (UPDRS), which allowed the relationship between symptom asymmetry and neural asymmetry to be assessed. We found that LD patients had stronger beta suppression during movement, as well as greater post-movement beta rebound compared to patients with RD symptoms, independent of the hand that was moved. Interestingly, the asymmetry of beta activity during right-hand movement uniquely correlated with symptom asymmetry, such that the more LD the symptom profile, the more left-lateralized (i.e., contralateral to movement) the beta response; conversely, the more RD the symptom profile, the more right-lateralized (i.e., ipsilateral to movement) the beta response. This study is the first to directly probe the relationship between symptom asymmetry and the laterality of neural activity during movement in patients with PD, and suggests that LD patients have a fundamentally different and more “healthy” oscillatory pattern relative to RD patients.

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Right-dominant expression of Parkinson's has been connected to faster progression.

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Linkage between symptom asymmetry and cortical physiology remains unknown.

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Cortical motor activity was measured in patients with left/right-dominant symptoms.

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Patients with left-dominant symptoms had “healthier” pattern of motor responses.

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Laterality of cortical activity during movement was related to symptom laterality.

Aberrant Neuronal Dynamics during Working Memory Operations in the Aging HIV-Infected Brain

Impairments in working memory are among the most prevalent features of HIV-associated neurocognitive disorders (HAND), yet their origins are unknown, with some studies arguing that encoding operations are disturbed and others supporting deficits in memory maintenance. The current investigation directly addresses this issue by using a dynamic mapping approach to identify when and where processing in working memory circuits degrades. HIV-infected older adults and a demographically-matched group of uninfected controls performed a verbal working memory task during magnetoencephalography (MEG). Significant oscillatory neural responses were imaged using a beamforming approach to illuminate the spatiotemporal dynamics of neuronal activity. HIV-infected patients were significantly less accurate on the working memory task and their neuronal dynamics indicated that encoding operations were preserved, while memory maintenance processes were abnormal. Specifically, no group differences were detected during the encoding period, yet dysfunction in occipital, fronto-temporal, hippocampal, and cerebellar cortices emerged during memory maintenance. In addition, task performance in the controls covaried with occipital alpha synchronization and activity in right prefrontal cortices. In conclusion, working memory impairments are common and significantly impact the daily functioning and independence of HIV-infected patients. These impairments likely reflect deficits in the maintenance of memory representations, not failures to adequately encode stimuli.

Transcranial direct-current stimulation modulates offline visual oscillatory activity: A magnetoencephalography study

Transcranial direct-current stimulation (tDCS) is a noninvasive neuromodulatory method that involves delivering low amplitude, direct current to specific regions of the brain. While a wealth of literature shows changes in behavior and cognition following tDCS administration, the underlying neuronal mechanisms remain largely unknown. Neuroimaging studies have generally used fMRI and shown only limited consensus to date, while the few electrophysiological studies have reported mostly null or counterintuitive findings. The goal of the current investigation was to quantify tDCS-induced alterations in the oscillatory dynamics of visual processing. To this end, we performed either active or sham tDCS using an occipital-frontal electrode configuration, and then recorded magnetoencephalography (MEG) offline during a visual entrainment task. Significant oscillatory responses were imaged in the time-frequency domain using beamforming, and the effects of tDCS on absolute and relative power were assessed. The results indicated significantly increased basal alpha levels in the occipital cortex following anodal tDCS, as well as reduced occipital synchronization at the second harmonic of the stimulus-flicker frequency relative to sham stimulation. In addition, we found reduced power in brain regions near the cathode (e.g., right inferior frontal gyrus [IFG]) following active tDCS, which was absent in the sham group. Taken together, these results suggest that anodal tDCS of the occipital cortices differentially modulates spontaneous and induced activity, and may interfere with the entrainment of neuronal populations by a visual-flicker stimulus. These findings also demonstrate the importance of electrode configuration on whole-brain dynamics, and highlight the deceptively complicated nature of tDCS in the context of neurophysiology.

Quiet connections: Reduced fronto-temporal connectivity in nondemented Parkinson's Disease during working memory encoding

Parkinson's disease (PD) is a common neurodegenerative disorder characterized primarily by motor symptoms such as bradykinesia, muscle rigidity, and resting tremor. It is now broadly accepted that these motor symptoms frequently co-occur with cognitive impairments, with deficits in working memory and attention being among the most common cognitive sequelae associated with PD. While these cognitive impairments are now recognized, the underlying neural dynamics and precise regions involved remain largely unknown. To this end, we examined the oscillatory dynamics and interregional functional connectivity that serve working memory processing in a group of unmedicated adults with PD and a matched group without PD. Each participant completed a high-load, Sternberg-type working memory task during magnetoencephalography (MEG), and we focused on the encoding and maintenance phases. All data were transformed into the time-frequency domain and significant oscillatory activity was imaged using a beamforming approach. Phase-coherence (connectivity) was also computed among the brain subregions exhibiting the strongest responses. Our most important findings were that unmedicated patients with PD had significantly diminished working memory performance (i.e., accuracy), and reduced functional connectivity between left inferior frontal cortices and left supramarginal-superior temporal cortices compared to participants without PD during the encoding phase of working memory processing. We conclude that patients with PD have reduced neural interactions between left prefrontal executive circuits and temporary verbal storage centers in the left supramarginal/superior temporal cortices during the stimulus encoding phase, which may underlie their diminished working memory function. Hum Brain Mapp 37:3224-3235, 2016. © 2016 Wiley Periodicals, Inc.

Neuroimaging with magnetoencephalography: A dynamic view of brain pathophysiology

Magnetoencephalography (MEG) is a noninvasive, silent, and totally passive neurophysiological imaging method with excellent temporal resolution (∼1 ms) and good spatial precision (∼3-5 mm). In a typical experiment, MEG data are acquired as healthy controls or patients with neurologic or psychiatric disorders perform a specific cognitive task, or receive sensory stimulation. The resulting data are generally analyzed using standard electrophysiological methods, coupled with advanced image reconstruction algorithms. To date, the total number of MEG instruments and associated users is significantly smaller than comparable human neuroimaging techniques, although this is likely to change in the near future with advances in the technology. Despite this small base, MEG research has made a significant impact on several areas of translational neuroscience, largely through its unique capacity to quantify the oscillatory dynamics of activated brain circuits in humans. This review focuses on the clinical areas where MEG imaging has arguably had the greatest impact in regard to the identification of aberrant neural dynamics at the regional and network level, monitoring of disease progression, determining how efficacious pharmacologic and behavioral interventions modulate neural systems, and the development of neural markers of disease. Specifically, this review covers recent advances in understanding the abnormal neural oscillatory dynamics that underlie Parkinson's disease, autism spectrum disorders, human immunodeficiency virus (HIV)-associated neurocognitive disorders, cerebral palsy, attention-deficit hyperactivity disorder, cognitive aging, and post-traumatic stress disorder. MEG imaging has had a major impact on how clinical neuroscientists understand the brain basis of these disorders, and its translational influence is rapidly expanding with new discoveries and applications emerging continuously.