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1.  Divergent Trajectories in the Aging Mind: Changes in Working Memory for Affective Versus Visual Information With Age 
Psychology and aging  2005;20(4):542-553.
Working memory mediates the short-term maintenance of information. Virtually all empirical research on working memory involves investigations of working memory for verbal and visual information. Whereas aging is typically associated with a deficit in working memory for these types of information, recent findings suggestive of relatively well-preserved long-term memory for emotional information in older adults raise questions about working memory for emotional material. This study examined age differences in working memory for emotional versus visual information. Findings demonstrate that, despite an age-related deficit for the latter, working memory for emotion was unimpaired. Further, older adults exhibited superior performance on positive relative to negative emotion trials, whereas their younger counterparts exhibited the opposite pattern.
doi:10.1037/0882-7974.20.4.542
PMCID: PMC2746384  PMID: 16420130
emotion; working memory; affect; cognition; positivity effect
2.  Neurocognitive Consequences of HIV Infection in Older Adults: An Evaluation of the “Cortical” Hypothesis 
AIDS and behavior  2011;15(6):1187-1196.
The incidence and prevalence of older adults living with HIV infection is increasing. Recent reports of increased neuropathologic and metabolic alterations in older HIV+ samples, including increased cortical beta-amyloid, have led some researchers to suggest that aging with HIV may produce a neuropsychological profile akin to that which is observed in “cortical” dementias (e.g., impairment in memory consolidation). To evaluate this possibility, we examined four groups classified by HIV serostatus and age (i.e., younger ≤40 years and older ≥50 years): (1) Younger HIV− (n = 24); (2) Younger HIV+ (n = 24); (3) Older HIV− (n = 20); and (4) Older HIV+ (n = 48). Main effects of aging were observed on episodic learning and memory, executive functions, and visuoconstruction, and main effects of HIV were observed on measures of verbal learning and memory. The interaction of age and HIV was observed on a measure of verbal recognition memory, which post hoc analyses showed to be exclusively attributed to the superior performance of the younger HIV seronegative group. Thus, in this sample of older HIV-infected individuals, the combined effects of HIV and aging do not appear to result in a “cortical” pattern of cognitive deficits.
doi:10.1007/s10461-010-9815-8
PMCID: PMC3110599  PMID: 20865313
Human immunodeficiency virus; Aging; Cognition; Neuropsychological tests; Episodic memory
3.  Neurocognitive Consequences of HIV Infection in Older Adults: An Evaluation of the “Cortical” Hypothesis 
AIDS and Behavior  2010;15(6):1187-1196.
The incidence and prevalence of older adults living with HIV infection is increasing. Recent reports of increased neuropathologic and metabolic alterations in older HIV+ samples, including increased cortical beta-amyloid, have led some researchers to suggest that aging with HIV may produce a neuropsychological profile akin to that which is observed in “cortical” dementias (e.g., impairment in memory consolidation). To evaluate this possibility, we examined four groups classified by HIV serostatus and age (i.e., younger ≤40 years and older ≥50 years): (1) Younger HIV− (n = 24); (2) Younger HIV+ (n = 24); (3) Older HIV− (n = 20); and (4) Older HIV+ (n = 48). Main effects of aging were observed on episodic learning and memory, executive functions, and visuoconstruction, and main effects of HIV were observed on measures of verbal learning and memory. The interaction of age and HIV was observed on a measure of verbal recognition memory, which post hoc analyses showed to be exclusively attributed to the superior performance of the younger HIV seronegative group. Thus, in this sample of older HIV-infected individuals, the combined effects of HIV and aging do not appear to result in a “cortical” pattern of cognitive deficits.
doi:10.1007/s10461-010-9815-8
PMCID: PMC3110599  PMID: 20865313
Human immunodeficiency virus; Aging; Cognition; Neuropsychological tests; Episodic memory
4.  An examination of the age-prospective memory paradox in HIV-infected adults 
The age-prospective memory (PM) paradox asserts that, despite evidence of age-associated PM deficits on laboratory tasks, older adults perform comparably to (or better than) young adults on naturalistic PM tasks. This study examined the age-PM paradox in older HIV-infected individuals, who represent a growing epidemic and may be at heightened risk for adverse neurocognitive and everyday functioning outcomes. Participants included 88 older (50+ years) and 53 younger (≤40 years) HIV-infected individuals as well as 54 older and 59 younger seronegative adults who completed both laboratory and naturalistic time-based PM tasks. Similar interactions were observed in both the seropositive and the seronegative samples, such that the older participants demonstrated significantly lower laboratory-based PM than the younger groups, but not on the naturalistic PM trial. Secondary analyses within the HIV+ sample revealed that naturalistic task success was indirectly associated with greater self-reported use of PM-based and external compensatory strategies in the daily lives of older, but not younger, HIV+ adults. Study findings suggest that, although older HIV-infected adults exhibit moderate PM deficits on laboratory measures versus their younger counterparts, such impairments are paradoxically not evident on ecologically relevant naturalistic PM activities in daily life, perhaps related to effective utilization compensatory strategies.
doi:10.1080/13803395.2011.604027
PMCID: PMC3327134  PMID: 21992453
Episodic memory; Aging; Neuropsychological assessment; AIDS dementia complex; Cognition
5.  Combined Effects of Aging and HIV Infection on Semantic Verbal Fluency: A View of the Cortical Hypothesis Through the Lens of Clustering and Switching 
The profile of HIV-associated neurocognitive disorders (HAND) has classically been characterized as “subcortical”, but questions have arisen as to whether aging with HIV in the antiretroviral therapy era has subtlety shifted the expression of HAND into a more “cortical” disorder (e.g., decay of semantic memory stores). We evaluated this hypothesis by examining semantic fluency and its component processes (i.e., clustering and switching) in 257 individuals across four groups stratified by age (<40 and ≥ 50 years) and HIV serostatus. Jonckheere-Terpstra tests revealed significant monotonic trends for the combined effects of HIV and aging on overall semantic (and letter) fluency and switching, but not cluster size, with greatest deficits evident in the older adults with HIV infection. Within the older HIV-infected cohort, poorer switching was uniquely associated with self-reported declines in instrumental activities of daily living and deficits in learning and executive functions, but not semantic memory. Results suggest that HIV infection and aging may confer adverse additive effects on the executive components of semantic fluency (i.e., switching), rather than a degradation of semantic memory stores (i.e., cluster size), which is a profile that is most consistent with combined frontostriatal neuropathological burden of these two conditions.
doi:10.1080/13803395.2011.651103
PMCID: PMC3329578  PMID: 22292479
Immunologic disorders; geropsychology; verbal fluency; executive functions; cognitive neuropsychology
6.  Aging, Neurocognition, and Medication Adherence in HIV Infection 
Objective
To evaluate the hypothesis that poor adherence to highly active antiretroviral treatment (HAART) would be more strongly related to cognitive impairment among older than among younger HIV-seropositive adults.
Setting and Participants
A volunteer sample of 431 HIV-infected adult patients prescribed self-administered HAART was recruited from community agencies and university-affiliated infectious disease clinics in the Los Angeles area.
Measurements
Neurocognitive measures included tests of attention, information processing speed, learning/memory, verbal fluency, motor functioning, and executive functioning. Medication adherence was measured using microchip-embedded pill bottle caps (Medication Event Monitoring System) and self-report. Latent/structural analysis techniques were used to evaluate factor models of cognition and adherence.
Results
Mean adherence rates were higher among older (≥50 years) than younger (<50 years) HIV-positive adults. However, latent/structural modeling demonstrated that neurocognitive impairment was associated with poorer medication adherence among older participants only. When cognitive subdomains were examined individually, executive functioning, motor functioning, and processing speed were most strongly related to adherence in this age group. CD4 count and drug problems were also more strongly associated with adherence among older than younger adults.
Conclusions
Older HIV-positive individuals with neurocognitive impairment or drug problems are at increased risk of suboptimal adherence to medication. Likewise, older adults may be especially vulnerable to immunological and neurocognitive dysfunction under conditions of suboptimal HAART adherence. These findings highlight the importance of optimizing medication adherence rates and evaluating neurocognition in the growing population of older HIV-infected patients.
doi:10.1097/JGP.0b013e31819431bd
PMCID: PMC2679810  PMID: 19307857
HIV; AIDS; aging; cognition; medication adherence; executive functions
7.  The aggregate effects of multiple comorbid risk factors on cognition among HIV-infected individuals 
This study developed and then cross-validated a novel weighting algorithm based on multiple comorbid risk factors (stimulant use, vascular disease, hepatitis C, HIV disease severity, cognitive reserve) to predict cognitive functioning among 366 HIV+ adults. The resultant “risk severity score” was used to differentially weight, as a function of age, the impact and magnitude of multiple risk factors on cognition. Among older adults (> 50 years) the risk severity index was differentially predictive of learning/memory and verbal fluency, whereas among younger adults it was linked to working memory and executive function. Cognitive reserve was found to be the most robust predictor of neurocognition.
doi:10.1080/13803395.2013.783000
PMCID: PMC3641576  PMID: 23547924
8.  Distinct mechanisms for the impact of distraction and interruption on working memory in aging 
Neurobiology of aging  2010;33(1):134-148.
Interference is known to negatively impact the ability to maintain information in working memory (WM), an effect that is exacerbated with aging. Here, we explore how distinct sources of interference, i.e., distraction (stimuli to-be-ignored) and interruption (stimuli requiring attention), differentially influence WM in younger and older adults. EEG was recorded while participants engaged in three versions of a delayed-recognition task: no interference, a distracting stimulus, and an interrupting stimulus presented during WM maintenance. Behaviorally, both types of interference negatively impacted WM accuracy in older adults significantly more than younger adults (with a larger deficit for interruptions). N170 latency measures revealed that the degree of processing both distractors and interruptors predicted WM accuracy in both populations. However, while WM impairments could be explained by excessive attention to distractors by older adults (a suppression deficit), impairment induced by interruption were not clearly mediated by age-related increases in attention to interruptors. These results suggest that distinct underlying mechanisms mediate the impact of different types of external interference on WM in normal aging.
doi:10.1016/j.neurobiolaging.2010.01.012
PMCID: PMC2891289  PMID: 20144492
EEG; aging; working memory; distraction; human
9.  Neuropsychiatric aspects of HIV infection among older adults 
Journal of clinical epidemiology  2001;54(Suppl 1):S44-S52.
Treatment advances such as the advent of highly active antiretroviral therapy (HAART) have translated into greater life expectancy for HIV-infected individuals, which will ultimately result in a “graying” of the HIV/AIDS epidemic. In addition, older individuals are engaging in a higher rate of high risk behaviors than had been previously expected. As such, study of older HIV-infected patients, including study of the psychiatric and neurocognitive aspects of the disease, appears highly indicated. Epidemiological studies have demonstrated that HIV infection is associated with higher rates of several psychological/psychiatric disorders when compared to general population base rates. There is also a rich literature that has documented the adverse neurocognitive effects of HIV infection, ranging from subtle cognitive complaints to frank dementia, among younger adults. Although it has been hypothesized that older age may potentiate the deleterious effects of HIV infection, little is actually known, however, regarding the incidence, prevalence, course, and clinical features of HIV-associated psychiatric and cognitive dysfunction among older adults. This article provides an overview of the epidemiology and clinical manifestations of HIV-associated cognitive and psychiatric disorder across the age spectrum, with particular focus on what is known regarding the interaction of advancing age and HIV infection. Future directions for research are suggested, including basic epidemiologic study of incidence and prevalence rates of neurodisease among older HIV-infected adults as well as investigations designed to determine whether the nature, severity, course, or treatment of such disorders differs among older versus younger patients.
PMCID: PMC2864032  PMID: 11750209
HIV infection; Older adults; Neuropsychiatric aspects
10.  The Semantic Relatedness of Cue-Intention Pairings Influences Event-Based Prospective Memory Failures in Older Adults with HIV Infection 
HIV infection and aging are each independently associated with prospective memory (ProM) impairment, which increases the risk of poor functional outcomes, including medication adherence. The incidence and prevalence of HIV infection among older adults has increased in recent years, thereby raising questions about the combined effects of these risk factors on ProM. In the present study, 118 participants were classified into four groups on the basis of HIV serostatus and age (i.e., ≤ 40 years and ≥ 50 years). Results showed significant additive effects of HIV and aging on event-based ProM, with the greatest deficits evident in the older HIV+ group, even after controlling for other demographic factors and potential medical, and psychiatric confounds. Event-based ProM impairment was particularly apparent in the older HIV+ group on trials for which the retrieval cue and intention were not semantically related. Worse performance on the semantically unrelated cue-intention trials was associated with executive dysfunction, older age, and histories of immunocompromise in the older HIV+ cohort. These data suggest that older HIV-infected adults are significantly less proficient at engaging the strategic encoding and retrieval processes required to a execute a future intention when the cue is unrelated to the intended action, perhaps secondary to greater neuropathological burden in the prefrontostriatal systems critical to optimal ProM functioning.
doi:10.1080/13803390903130737
PMCID: PMC2854853  PMID: 19763997
Human immunodeficiency virus; Episodic memory; aging; AIDS dementia complex; multi-process theory
11.  Successful cognitive aging in persons living with HIV infection 
Journal of Neurovirology  2010;17(1):110-119.
The number of older adults living with human immunodeficiency virus (HIV) infection is growing and this subpopulation of the epidemic is at heightened risk for a variety of poor health outcomes including HIV-associated neurocognitive disorders. The current study sought to examine the factors associated with freedom from neurocognitive impairment in older HIV-infected adults. Participants included 74 middle-aged and older (mean age 51 years), HIV-infected individuals with a mean estimated duration of infection of 17 years who underwent comprehensive neuropsychological, psychiatric, and medical evaluations. Successful cognitive aging (SCA) was operationally defined as the absence of neurocognitive deficits as determined by a battery of well-validated cognitive tests and self-endorsed cognitive complaints. Thirty-two percent of the cohort met these criteria. Compared to the group that did not meet these criteria, successful cognitive agers had significantly lower lifetime rates of major depressive disorder and current affective distress (e.g., depression, anxiety). Moreover, the SCA group evidenced better everyday functioning outcomes, including medication adherence, lower self-reported rates of declines in activities of daily living, and superior abilities related to medication management and dealing with healthcare providers. SCA was not related to demographic composition, HIV disease or treatment factors, medical comorbidities, or histories of substance use disorders. Findings from this preliminary study suggest that approximately one-third of older persons with HIV were free of cognitive impairments, which is associated with more favorable emotional, psychosocial, and everyday functioning.
doi:10.1007/s13365-010-0008-z
PMCID: PMC3032198  PMID: 21165783
Neuropsychological assessment; Aging; Treatment adherence; AIDS dementia; Depression
12.  Can Training in a Real-Time Strategy Videogame Attenuate Cognitive Decline in Older Adults? 
Psychology and aging  2008;23(4):765-777.
Declines in various cognitive abilities, particularly executive control functions, are observed in older adults. An important goal of cognitive training is to slow or reverse these age-related declines. However, opinion is divided in the literature regarding whether cognitive training can engender transfer to a variety of cognitive skills in older adults. Yet, recent research indicates that videogame training of young adults may engender broad transfer to skills of visual attention. In the current study, we used a real-time strategy videogame to attempt to train executive functions in older adults, such as working memory, task switching, short-term memory, inhibition, and reasoning. Older adults were either trained in a real-time strategy videogame for 23.5 hours (RON, n=20) or not (CONTROLS, n=20). A battery of cognitive tasks, including tasks of executive control and visuo-spatial skills, were assessed before, during, and after video game training. The trainees improved significantly in the measures of game performance. They also improved significantly more than the controls in a subset of the cognitive tasks, such as task switching, working memory, visual short term memory, and mental rotation. Trends in improvement were also observed, for the video game trainees, in inhibition and reasoning. Individual differences in changes in game performance were correlated with improvements in task-switching. The study has implications for the enhancement of executive control processes of older adults.
doi:10.1037/a0013494
PMCID: PMC4041116  PMID: 19140648
Cognitive training; aging; executive control; videogame; transfer of training
13.  Effects of traumatic brain injury on cognitive functioning and cerebral metabolites in HIV-infected individuals 
We explored the possible augmenting effect of traumatic brain injury (TBI) history on HIV (human immunodeficiency virus) associated neurocognitive complications. HIV-infected participants with self-reported history of definite TBI were compared to HIV patients without TBI history. Groups were equated for relevant demographic and HIV-associated characteristics. The TBI group evidenced significantly greater deficits in executive functioning and working memory. N-acetylaspartate, a putative marker of neuronal integrity, was significantly lower in the frontal gray matter and basal ganglia brain regions of the TBI group. Together, these results suggest an additional brain impact of TBI over that from HIV alone. One clinical implication is that HIV patients with TBI history may need to be monitored more closely for increased risk of HIV-associated neurocognitive disorder signs or symptoms.
doi:10.1080/13803395.2010.518140
PMCID: PMC3062232  PMID: 21229435
Head injury; HIV associated neurocognitive disorder; Neuropsychological performance; Magnetic resonance spectroscopy; N-acetylaspartate
14.  The Relationship between Visual-Spatial and Auditory-Verbal Working Memory Span in Senegalese and Ugandan Children 
PLoS ONE  2010;5(1):e8914.
Background
Using the Kaufman Assessment Battery for Children (K-ABC) Conant et al. (1999) observed that visual and auditory working memory (WM) span were independent in both younger and older children from DR Congo, but related in older American children and in Lao children [1]. The present study evaluated whether visual and auditory WM span were independent in Ugandan and Senegalese children.
Method
In a linear regression analysis we used visual (Spatial Memory, Hand Movements) and auditory (Number Recall) WM along with education and physical development (weight/height) as predictors. The predicted variable in this analysis was Word Order, which is a verbal memory task that has both visual and auditory memory components.
Results
Both the younger (<8.5 yrs) and older (>8.5 yrs) Ugandan children had auditory memory span (Number Recall) that was strongly predictive of Word Order performance. For both the younger and older groups of Senegalese children, only visual WM span (Spatial Memory) was strongly predictive of Word Order. Number Recall was not significantly predictive of Word Order in either age group.
Conclusions
It is possible that greater literacy from more schooling for the Ugandan age groups mediated their greater degree of interdependence between auditory and verbal WM. Our findings support those of Conant et al., who observed in their cross-cultural comparisons that stronger education seemed to enhance the dominance of the phonological-auditory processing loop for WM.
doi:10.1371/journal.pone.0008914
PMCID: PMC2811730  PMID: 20111706
15.  The Impact of Visual Distraction on Episodic Retrieval in Older Adults 
Brain research  2011;1430:78-85.
Impairment in long-term memory is one of the most salient alterations in cognitive aging. Findings of age-related deficits in source monitoring and recollection have revealed a selective decline in memory for detailed information. The underlying mechanism of this phenomenon is not well understood. We hypothesized that the influence of task-irrelevant visual stimuli present in our environment interferes with retrieval of detailed memories more for older than younger adults. We compared memory performance on a recall test for visual details when older adult participants’ eyes were closed versus performance when their eyes were open and irrelevant visual stimuli were presented. The results showed that the presence of irrelevant visual information diminished long-term memory performance based on an objective measure of recollection for visual details. Comparison of the current results to findings from our earlier study using the same experimental paradigm with younger adults revealed that visual distraction disrupted recollection of relevant details to a greater degree in older than younger adults. This result suggests that visual distraction overwhelms older adults’ declining cognitive control resources that are instrumental in the retrieval and selection of mnemonic details. More generally, these findings explicate a mechanistic basis for selective impairment of recollection in normal aging.
doi:10.1016/j.brainres.2011.10.048
PMCID: PMC3242871  PMID: 22119398
recollection; aging; interference; cognitive control
16.  Abnormal MEG Oscillatory Activity during Visual Processing in the Prefrontal Cortices and Frontal Eye-Fields of the Aging HIV Brain 
PLoS ONE  2013;8(6):e66241.
Objective
Shortly after infection, HIV enters the brain and causes widespread inflammation and neuronal damage, which ultimately leads to neuropsychological impairments. Despite a large body of neuroscience and imaging studies, the pathophysiology of these HIV-associated neurocognitive disorders (HAND) remains unresolved. Previous neuroimaging studies have shown greater activation in HIV-infected patients during strenuous tasks in frontal and parietal cortices, and less activation in the primary sensory cortices during rest and sensory stimulation.
Methods
High-density magnetoencephalography (MEG) was utilized to evaluate the basic neurophysiology underlying attentive, visual processing in older HIV-infected adults and a matched non-infected control group. Unlike other neuroimaging methods, MEG is a direct measure of neural activity that is not tied to brain metabolism or hemodynamic responses. During MEG, participants fixated on a centrally-presented crosshair while intermittent visual stimulation appeared in their top-right visual-field quadrant. All MEG data was imaged in the time-frequency domain using beamforming.
Results
Uninfected controls had increased neuronal synchronization in the 6–12 Hz range within the right dorsolateral prefrontal cortex, right frontal eye-fields, and the posterior cingulate. Conversely, HIV-infected patients exhibited decreased synchrony in these same neural regions, and the magnitude of these decreases was correlated with neuropsychological performance in several cortical association regions.
Conclusions
MEG-based imaging holds potential as a noninvasive biomarker for HIV-related neuronal dysfunction, and may help identify patients who have or may develop HAND. Reduced synchronization of neural populations in the association cortices was strongly linked to cognitive dysfunction, and likely reflects the impact of HIV on neuronal and neuropsychological health.
doi:10.1371/journal.pone.0066241
PMCID: PMC3688779  PMID: 23840428
17.  Aging, Prospective Memory, and Health-Related Quality of Life in HIV Infection 
AIDS and behavior  2012;16(8):2309-2318.
HIV infection and older age are each independently associated with lower health-related quality of life (HRQoL) and deficits in prospective memory (PM), which is a distinct aspect of cognition involving the ability to “remember to remember” to do something at a future occasion. The present study investigated associations between PM and HRQoL in 72 older (≥ 50 years) and 41 younger (≤ 40 years) HIV-infected adults. Self-reported PM complaints predicted HRQoL across the entire sample, but there was a significant interaction between performance-based PM and age group on HRQoL, such that lower time-based PM was associated with lower HRQoL only in the younger cohort. Within the younger group, time-based and self-reported PM significantly predicted mental HRQoL independent of other risk factors (e.g., depression). These findings suggest that PM plays a unique role in HRQoL outcomes among younger persons living with HIV infection and support the examination of other age-related factors (e.g., effective use of compensatory strategies) that may regulate the adverse impact of PM on everyday functioning.
doi:10.1007/s10461-011-0121-x
PMCID: PMC3352996  PMID: 22246512
AIDS Dementia Complex; Aging; Prospective memory; Quality of life; Functional status; Health status
18.  Prepulse Inhibition in HIV-Associated Neurocognitive Disorders 
Sensorimotor inhibition, or the ability to filter out excessive or irrelevant information, theoretically supports a variety of higher-level cognitive functions. Impaired inhibition may be associated with increased impulsive and risky behavior in everyday life. Individuals infected with HIV frequently show impairment on tests of neurocognitive function, but sensorimotor inhibition in this population has not been studied and may be a contributor to the profile of HIV-associated Neurocognitive Disorders (HAND). 37 HIV-infected individuals (15 with HAND) and 48 non-infected comparison subjects were assessed for prepulse inhibition (PPI), an eyeblink startle paradigm measuring sensorimotor gating. Although HIV status alone was not associated with PPI deficits, HIV-positive participants meeting criteria for HAND showed impaired PPI compared to cognitively intact HIV-positive subjects. In HIV-positive subjects, PPI was correlated with working memory but was not associated with antiretroviral therapy or illness factors. In conclusion, sensorimotor disinhibition in HIV accompanies deficits in higher-order cognitive functions, though the causal direction of this relationship requires investigation. Subsequent research on the role of sensorimotor gating on decision-making and risk behaviors in HIV may be indicated.
doi:10.1017/S1355617713000301
PMCID: PMC3729041  PMID: 23552464
sensorimotor gating; AIDS dementia complex; cognition; startle; working memory; impulsivity
19.  Seven-year-olds Allocate Attention Like Adults Unless Working Memory is Overloaded 
Developmental science  2010;13(1):120.
Previous studies indicate that visual working memory performance increases with age in childhood but it is not clear why. One main hypothesis has been that younger children are less efficient in their attention, specifically less able to exclude irrelevant items from working memory to make room for relevant items. We examined this hypothesis by measuring visual working memory capacity under a continuum of 5 attention conditions. A recognition advantage was found for items to be attended as opposed to ignored. The size of this attention-related effect was adult-like in young children with small arrays, suggesting that their attention processes are efficient even though their working memory capacity is smaller than that of older children and adults. With a larger working memory load, this efficiency in young children is compromised. The efficiency of attention cannot be the sole explanation for the capacity difference.
doi:10.1111/j.1467-7687.2009.00864.x
PMCID: PMC2819460  PMID: 20121868
20.  Rule-Based Category Learning in Children: The Role of Age and Executive Functioning 
PLoS ONE  2014;9(1):e85316.
Rule-based category learning was examined in 4–11 year-olds and adults. Participants were asked to learn a set of novel perceptual categories in a classification learning task. Categorization performance improved with age, with younger children showing the strongest rule-based deficit relative to older children and adults. Model-based analyses provided insight regarding the type of strategy being used to solve the categorization task, demonstrating that the use of the task appropriate strategy increased with age. When children and adults who identified the correct categorization rule were compared, the performance deficit was no longer evident. Executive functions were also measured. While both working memory and inhibitory control were related to rule-based categorization and improved with age, working memory specifically was found to marginally mediate the age-related improvements in categorization. When analyses focused only on the sample of children, results showed that working memory ability and inhibitory control were associated with categorization performance and strategy use. The current findings track changes in categorization performance across childhood, demonstrating at which points performance begins to mature and resemble that of adults. Additionally, findings highlight the potential role that working memory and inhibitory control may play in rule-based category learning.
doi:10.1371/journal.pone.0085316
PMCID: PMC3906381  PMID: 24489658
21.  Does Differential Strategy Use Account for Age-Related Deficits in Working-Memory Performance? 
Psychology and aging  2009;24(1):82-92.
The strategy-deficit hypothesis states that age differences in the use of effective strategies contribute to the age-related deficits in working memory (WM) span performance. To evaluate this hypothesis, strategy use was measured using set-by-set strategy reports during the reading span (RSPAN) task (Experiments 1 and 2) and the operation span (OSPAN) task (Experiment 2). Individual differences in the reported use of effective strategies accounted for substantial variance in span performance. In contrast to the strategy-deficit hypothesis, however, young and older adults reported using the same proportion of normatively effective strategies on both span tasks. Measures of processing speed accounted for a substantial proportion of the age-related variance in span performance. Thus, although using normatively effective strategies accounts for individual differences in span performance, age differences in effective strategy use cannot explain the age-related variance in that performance.
doi:10.1037/a0014078
PMCID: PMC2658624  PMID: 19290740
22.  Intraindividual Variability in HIV Infection: Evidence for Greater Neurocognitive Dispersion in Older HIV Seropositive Adults 
Neuropsychology  2011;25(5):645-654.
Objective
Both the prevalence and incidence of HIV infection among older adults are on the rise. Older adults are at increased risk of HIV-associated neurocognitive disorders, which has historically been characterized as an inconsistent or “spotty” pattern of deficits. Dispersion is a form of intraindividual variability (IIV) that is defined as within-person variability in performance across domains and has been associated with poorer neurocognitive functioning and incipient decline among healthy older adults. To our knowledge, no studies have yet examined dispersion in an aging HIV-infected sample.
Methods
For the current study we examined the hypothesis that age and HIV infection have synergistic effects on dispersion across a battery of clinical and experimental cognitive tasks. Our well-characterized sample comprised 126 HIV-seropositive individuals (HIV+) and 40 HIV-seronegative comparison individuals (HIV−), all of whom were administered a comprehensive neuropsychological battery.
Results
Consistent with our hypothesis, an age by HIV serostatus interaction was observed, with the older HIV+ group demonstrating a higher level of dispersion relative to older HIV− and younger HIV+ individuals, even when potentially confounding demographic and medical factors were controlled.
Conclusion
Our results demonstrate that older HIV+ adults produce greater dispersion, or intraindividual variability in performance across a range of tests, which may be reflective of cognitive dyscontrol to which this population is vulnerable, perhaps driven by the combined effects of aging and HIV infection on prefrontostriatal systems.
doi:10.1037/a0023792
PMCID: PMC3158302  PMID: 21574712
HIV; aging; neuropsychological assessment; variability
23.  Prolonged disengagement from attentional capture in normal aging 
Psychology and aging  2012;28(1):77-86.
Older adults are more vulnerable to a negative impact of irrelevant information on cognitive performance. We used a psychophysical approach to evaluate which aspects of distraction are altered in aging: susceptibility for attention to be captured by a distractor, or the timing of disengagement from processing a distractor. We found that younger and older adults were equally susceptible to a detrimental influence of attentional capture on target detection in the initial moments after distractor presentation, but older adults exhibited a longer time window for the negative effects of capture to resolve. As was recently shown in younger adults, the timing of disengagement from capture correlated with individual differences in visual working memory capacity in the older cohort. These results suggest that the larger impact by distraction on perceptual abilities in normal aging is not the result of a greater susceptibility to attentional capture by distraction, but rather prolonged processing of distractors.
doi:10.1037/a0029899
PMCID: PMC3586289  PMID: 23066799
Older adults; perception; working memory; visual capture
24.  Age-related impairments in active learning and strategic visual exploration 
Old age could impair memory by disrupting learning strategies used by younger individuals. We tested this possibility by manipulating the ability to use visual-exploration strategies during learning. Subjects controlled visual exploration during active learning, thus permitting the use of strategies, whereas strategies were limited during passive learning via predetermined exploration patterns. Performance on tests of object recognition and object-location recall was matched for younger and older subjects for objects studied passively, when learning strategies were restricted. Active learning improved object recognition similarly for younger and older subjects. However, active learning improved object-location recall for younger subjects, but not older subjects. Exploration patterns were used to identify a learning strategy involving repeat viewing. Older subjects used this strategy less frequently and it provided less memory benefit compared to younger subjects. In previous experiments, we linked hippocampal-prefrontal co-activation to improvements in object-location recall from active learning and to the exploration strategy. Collectively, these findings suggest that age-related memory problems result partly from impaired strategies during learning, potentially due to reduced hippocampal-prefrontal co-engagement.
doi:10.3389/fnagi.2014.00019
PMCID: PMC3924049  PMID: 24592236
active learning; memory; aging; age-related memory impairment; vicarious trial-and-error behavior; hippocampus; prefrontal cortex; revisitation
25.  Neuropsychological Dysfunction among HIV Infected Drug Abusers 
Human immunodeficiency virus (HIV) has been documented to cause direct and indirect central nervous system dysfunction that can be observed as a progressive decline in neuropsychological functioning in a large proportion of persons with HIV and AIDS. Neuropsychological decline in individuals with HIV is characterized by cognitive and motor slowing, attentional deficits, executive dysfunction and memory impairment (characterized by intact recognition and deficits in learning and delayed recall). Dementia occurs in a relatively small proportion of HIV infected individuals, though milder NP deficits are observed in 30-50% of persons with advanced disease. Recent evidence suggests that drug users, especially stimulant users, are at risk for accelerated progression of their HIV disease, including a greater risk of neuropsychological dysfunction. Methamphetamine may potentiate HIV Tat protein mediated neurotoxicity giving rise to striatal proinflammatory cytokine stimulation and activation of redox-regulated transcription factors. Oxidative stress due to mitochondrial dysfunction is another candidate process underlying the synergistic effects of stimulant use and HIV. Damage to neurotransmitter systems including the dopaminergic, serotonergic and glutamatergic systems which are affected by both stimulant use and HIV is an alternate explanation. Methamphetamine has also been shown to impede the effectiveness of HAART, which could then in turn allow for more rapid HIV disease progression. A greater prevalence of psychiatric disorders, particularly mood, anxiety and substance use disorders are also observed in HIV positive samples relative to the general population. The changing nature of the HIV pandemic is an ongoing challenge to investigators and clinicians working in this field. Emerging issues requiring additional attention are study of the interactive effects of normal aging and HIV on neurocognition as well as study of the effects of co-infection with Hepatitis C.
PMCID: PMC2868271  PMID: 20467580
HIV; AIDS; Neuropsychology; Drug Abuse

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