Vaughn E. Bryant

Effects of Electrode Drift in Transcranial Direct Current Stimulation

BACKGROUND Conventional transcranial direct current stimulation (tDCS) methods involve application of weak electrical current through electrodes encased in saline-soaked sponges affixed to the head using elastic straps. In the absence of careful preparation, electrodes can drift from their original location over the course of a tDCS session. OBJECTIVE The current paper investigates the influence of electrode drift on distribution of electric fields generated by conventional tDCS. METHODS MRI-derived finite element models of electric fields produced by tDCS were used to investigate the influence of incremental drift in electrodes for two of the most common electrode montages used in the literature: M1/SO (motor to contralateral supraorbital) and F3/F4 (bilateral frontal). Based on these models, we extracted predicted current intensity from 20 representative structures in the brain. RESULTS Results from separate RM-ANOVAs for M1/SO and F3/F4 montages demonstrated that 5% incremental drift in electrode position significantly changed the distribution of current delivered by tDCS to the human brain (Fs > 8.6, Ps < 0.001). Pairwise comparisons demonstrated that as little as 5% drift was able to produce significant differences in current intensity in structures distributed across the brain (Ps < 0.03). CONCLUSIONS Drift in electrode position during a session of tDCS produces significant alteration in the intensity of stimulation delivered to the brain. Elimination of this source of variability will facilitate replication and interpretation of tDCS findings. Furthermore, measurement and statistically accounting for drift may prove important for better characterizing the effects of tDCS on the human brain and behavior.

The effects of cigarette smoking on learning and memory performance among people living with HIV/AIDS

The purpose of this study was to examine the effects of smoking (past and current) on multiple domains of cognitive functioning in a sample of people living with HIV/AIDS (PLWHA). We hypothesized that among PLWHA, current smokers would demonstrate poorer cognitive functioning when compared to non-smokers, specifically in the cognitive domains of auditory-verbal learning and memory, visuospatial memory, overall cognitive efficiency, executive skills, processing speed, and working memory. Results suggest that in patients being treated for HIV infection, current smoking is negatively associated with learning, memory, and global cognitive functioning. There was also some evidence that cognitive deficits in learning associated with smoking were more pronounced among men compared to women. However, the cause of these effects is not at all clear. In multivariate models, the differences associated with smoking were non-significant when adjusting for education and hepatitis C virus infection. Therefore, smoking may simply reflect a general tendency to more widespread deficits and comorbidities rather than directly impacting cognitive function. Future studies should attempt to examine a priori cognitive factors which contribute to smoking debut and other associated risk factors in order to understand why smoking may be a marker for other risk factors and may ultimately influence neurocognitive functioning critical to daily activities and adherence.

Frontal Structural Neural Correlates of Working Memory Performance in Older Adults

Working memory is an executive memory process that allows transitional information to be held and manipulated temporarily in memory stores before being forgotten or encoded into long-term memory. Working memory is necessary for everyday decision-making and problem solving, making it a fundamental process in the daily lives of older adults. Working memory relies heavily on frontal lobe structures and is known to decline with age. The current study aimed to determine the neural correlates of decreased working memory performance in the frontal lobes by comparing cortical thickness and cortical surface area from two demographically matched groups of healthy older adults, free from cognitive impairment, with high versus low N-Back working memory performance (N = 56; average age = 70.29 ± 10.64). High-resolution structural T1-weighted images (1 mm isotropic voxels) were obtained on a 3T Philips MRI scanner. When compared to high performers, low performers exhibited significantly decreased cortical surface area in three frontal lobe regions lateralized to the right hemisphere: medial orbital frontal gyrus, inferior frontal gyrus, and superior frontal gyrus (FDR p < 0.05). There were no significant differences in cortical thickness between groups, a proxy for neurodegenerative tissue loss. Our results suggest that decreases in cortical surface area (a proxy for brain structural integrity) in right frontal regions may underlie age-related decline of working memory function.

Factors Influencing Clinical Correlates of Chronic Traumatic Encephalopathy (CTE): a Review.

Chronic traumatic encephalopathy (CTE) is a neuropathologically defined disease reportedly linked to a history of repetitive brain trauma. As such, retired collision sport athletes are likely at heightened risk for developing CTE. Researchers have described distinct pathological features of CTE as well a wide range of clinical symptom presentations, recently termed traumatic encephalopathy syndrome (TES). These clinical symptoms are highly variable, non-specific to individuals described as having CTE pathology in case reports, and are often associated with many other factors. This review describes the cognitive, emotional, and behavioral changes associated with 1) developmental and demographic factors, 2) neurodevelopmental disorders, 3) normal aging, 4) adjusting to retirement, 5) drug and alcohol abuse, 6) surgeries and anesthesia, and 7) sleep difficulties, as well as the relationship between these factors and risk for developing dementia-related neurodegenerative disease. We discuss why some professional athletes may be particularly susceptible to many of these effects and the importance of choosing appropriate controls groups when designing research protocols. We conclude that these factors should be considered as modifiers predominantly of the clinical outcomes associated with repetitive brain trauma within a broader biopsychosocial framework when interpreting and attributing symptom development, though also note potential effects on neuropathological outcomes. Importantly, this could have significant treatment implications for improving quality of life.

The Continuing Challenge of Reducing HIV Risk among Haitian Youth The Need for Intervention

There is a dire need for interventions that will address the multiple factors—poverty, substance use, early sexual debut, and violence—that influence Haitian youth’s engagement in risky behaviors. The deteriorating socioeconomic and political state of the country has had a deleterious effect on the sociocultural milieu and on the boundaries that have heretofore kept risky behaviors in check. Historically, the lakou system, a community-based approach that supports the family unit, has disintegrated, leading to the disruption of traditional parenting patterns. The unstable economic system has also led to the increasing use of children from poor families, who through the restavek system, are sent to work as servants in other households. The breakdown of traditional systems, coupled with the increasing economic and political instability, has had a significant effect on Haitian adolescents. Among boys, increased levels of substance use have been associated with multiple sex partnerships and very early sexual debut. Among girls, extremely high rates of sexual abuse and forced sex have led to relatively high levels of HIV. While the majority of them have been exposed to behavior change messages, behavior change itself has lagged because many adolescents do not accurately perceive their risk exposure. This review explores the risks of HIV transmission among Haitian youth, with a focus on vulnerability factors, including substance use, culture, and the socioeconomic context, and provides recommendations for intervention. An ecosystemic approach, designed specifically for Haitian youth and that takes environmental context and culture into account, is needed.

Low cholesterol? Don't brag yet ... hypocholesterolemia blunts HAART effectiveness: a longitudinal study

BackgroundIn vitro studies suggest that reducing cholesterol inhibits HIV replication. However, this effect may not hold in vivo, where other factors, such as cholesterols immunomodulatory properties, may interact.MethodsFasting blood samples were obtained on 165 people living with HIV at baseline and after 24 weeks on highly active antiretroviral therapy (HAART). Participants were classified as hypocholesterolemic (HypoCHL; <150 mg/dl) or non-HypoCHL (>150 mg/dl) and were compared on viro-immune outcomes.ResultsAt baseline, participants with HypoCHL (40%) exhibited lower CD4 (197 ± 181 vs. 295 ± 191 cells/mm3, p = 0.02) and CD8 (823 ± 448 vs. 1194 ± 598 cells/mm3, p = 0.001) counts and were more likely to have detectable viral loads (OR = 3.5, p = 0.01) than non-HypoCHL controls. After HAART, participants with HypoCHL were twice as likely to experience a virological failure >400 copies (95% CI 1-2.6, p = 0.05) and to exhibit <200 CD4 (95% CI 1.03-2.9, p = 0.04) compared with non-HypoCHL. Low thymic output was related to poorer CD4 cell response in HypoCHL subjects. Analyses suggest a dose-response relationship with every increase of 50 mg/dl in cholesterol related to a parallel rise of 50 CD4 cells.ConclusionsThe study implicates, for the first time, HypoCHL with impaired HAART effectiveness, including limited CD4 repletion by the thymus and suboptimal viral clearance.

Loneliness and substance use: the influence of gender among HIV+ Black/African American adults 50+

ABSTRACT Estimates suggest 30% of adults report the highest levels of loneliness. Though men are more likely than women to use illicit substances and engage in heavy drinking, the prevalence of substance use in women is growing and their escalation toward dependence occurs more rapidly. Loneliness and substance use have greater relevance within the HIV+ population, with higher rates of substance misuse than the general population. However, the association between loneliness and substance use within HIV+ individuals remains understudied. The purpose of the present study was to test the hypothesis that there would be an association between loneliness and substance moderated by gender in HIV+ older adults. A cross-sectional study was conducted between October 2013 and January 2014. Study participants included 96 HIV-positive Black/African American men and women recruited through the University of Florida Center for HIV/AIDS Research, Education and Service (UF CARES) in Jacksonville, Florida. Participants completed an interviewer-administered assessment examining mental and behavioral health. Pearson correlations examined associations between loneliness and substance use. Binary logistic regression analyses stratified by gender examined the association between loneliness and substance use while controlling for covariates. Among women, loneliness was associated with illicit drug use, AOR = 3.37, 95% CI: 1.23–9.21, p = .018 and heavy drinking, AOR = 2.47, 95% CI: 1.07–5.71, p = .033. No significant associations were found between loneliness and illicit drug use, and heavy drinking in men. Substance use among women in this population may be linked to loneliness. Interventions should be gender specific. Further research into this association is necessary as it will likely have important clinical implications for this population.

Brain Derived Neurotrophic Factor and Cognitive Status: The Delicate Balance Among People Living with HIV, with and without Alcohol Abuse

INTRODUCTION The advent of combination antiretroviral therapy(cART) has lead to a significant reduction in morbidity and mortality among people living with HIV(PLWH). However, HIV-associated neurocognitive disorders (HAND) still remain a significant problem. One possible mechanism for the persistence of these disorders is through the effect of HIV on brain-derived neurotrophic factor (BDNF). BDNF is influenced by various factors including hazardous alcohol use (HAU), which is prevalent among PLWH. This study attempts to elucidate the relationships between HAU, BDNF and HAND. METHODS Cross-sectional analyses were conducted on a sample of 199 hazardous alcohol users and 198 non-HAU living with HIV. Members of each group were matched according to sociodemographic characteristics and CD4 count. Research procedures included validated questionnaires, neuropsychological assessments and a blood sample to obtain BDNF and immune measurements. RESULTS Hazardous alcohol users showed either significantly lower or significantly higher BDNF levels compared to the Non-hazardous (OR=1,4; 95% CI: 1-2.1, p = 0.003). Therefore, for additional analyses, subjects were categorized based on BDNF values in: Group 1 < 4000, Group 2: 4001-7,999 (reference group), and Group 3 for those >8,000 pg/mL. Groups 1 and 3 performed significantly worse than those in Group 2 in the domains of processing speed, auditory-verbal and visuospatial learning and memory. Multivariate analyses confirmed that HAU and BDNF are significant contributors of HAND. CONCLUSION Our findings offer novel insights into the relationships between BDNF, and alcohol use among PLWH. Our results also lend support to expanding clinical movement to use BDNF as an intervention target for PLWH, in those with evidence of deficiencies, and highlight the importance of including HAUat the inception of clinical trials.

Depression and Apathy Among People Living with HIV: Implications for Treatment of HIV Associated Neurocognitive Disorders

Depression and apathy are common among people living with HIV (PLWH). However, in PLWH, it is unclear whether depression and apathy are distinct conditions, which contribute to different patterns of disruption to cognitive processing and brain systems. Understanding these conditions may enable the development of prognostic indicators for HIV associated neurocognitive disorders (HAND). The present study examined substance use behavior and cognitive deficits, associated with depression and apathy, in 120 PLWH, using hierarchical regression analyses. Higher levels of depression were associated with a history of alcohol dependence and greater deficits in processing speed, motor and global cognitive functioning. Higher levels of apathy were associated with a history of cocaine dependence. It is recommended that PLWH get screened appropriately for apathy and depression, in order to receive the appropriate treatment, considering the comorbidities associated with each condition. Future research should examine the neurological correlates of apathy and depression in PLWH.

Body mass index, inflammatory biomarkers and neurocognitive impairment in HIV-infected persons

Abstract To determine the relationships among body mass index (BMI), and HIV-associated neurocognitive impairment and the potential mediating effects of inflammatory cytokines. Among the HIV-infected individuals (N = 90) included in this study, obesity was associated with slower processing speed (β = −.229, standard error (SE) = 2.15, p = .033), compared to participants with a normal BMI, after controlling for psychosocial and HIV clinical factors. Serum concentrations of the interleukin-16 (IL-16) cytokine were significantly associated with slowed processing speed (β = −.235, SE = 1.62, p = .033) but did not mediate the relationship between obesity and processing speed These findings suggest that obesity may contribute to cognitive processing speed deficits in HIV-infected adults. Elevated concentrations of IL-16 are also associated with slowing, though the results suggest that obesity and IL-16 may exert independent effects.