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Shu-Chen Li

Publications and source records attributed to Shu-Chen Li.

15 recordsLinked to original sources
PubMed2006

Neuromodulation of associative and organizational plasticity across the life span: empirical evidence and neurocomputational modeling.

Developmental plasticity is the key mechanism that allows humans and other organisms to modify and adapt to contextual and experiential influences. Thus, reciprocal co-constructive interactions between behavioral and neuronal plasticity play important roles in regulating neurobehavioral development across the life span. This review focuses on behavioral and neuronal evidence of lifespan differences in associative memory plasticity and plasticity of the functional organization of cognitive and cortical processes, as well as the role of the dopaminergic system in modulating such plasticity. Special attention is given to neurocomputational models that help exploring lifespan differences in neuromodulation of neuronal and behavioral plasticity. Simulation results from these models suggest that lifespan changes in the efficacy of neuromodulatory mechanisms may shape associative memory plasticity and the functional organization of neurocognitive processes by affecting the fidelity of neuronal signal transmission, which has consequences for the distinctiveness of neurocognitive representations and the efficacy of distributed neural coding.

Animals↗
PubMed2006

Cortical EEG correlates of successful memory encoding: implications for lifespan comparisons.

In the course of their lives, individuals experience a myriad of events. Some of them leave stable traces, and others fade away quickly. Recent advances in functional imaging methods allow researchers to contrast neuronal patterns of remembered against not remembered events at initial encoding. Research on young adults using functional magnetic resonance imaging (fMRI), intracranial, and standard electroencephalographic (EEG) recordings has identified differences between remembered and not remembered items in patterns of medio-temporal and prefrontal brain activity. However, little is known about the ways in which such neuronal patterns of successful encoding evolve across the lifespan as a function of maturation, senescence, and the accumulation of experience. Here, we first review empirical evidence on neuronal correlates of successful memory from middle childhood to old age. Based on the observation that associative and strategic components of episodic memory seem to follow different age gradients, we propose a conceptual framework for predicting age changes in neuronal patterns of successful encoding.

Age Factors↗
PubMed2006

The correlative triad among aging, dopamine, and cognition: current status and future prospects.

The brain neuronal systems defined by the neurotransmitter dopamine (DA) have since long a recognized role in the regulation of motor functions. More recently, converging evidence from patient studies, animal research, pharmacological intervention, and molecular genetics indicates that DA is critically implicated also in higher-order cognitive functioning. Many cognitive functions and multiple markers of striatal and extrastriatal DA systems decline across adulthood and aging. Research examining the correlative triad among adult age, DA, and cognition has found strong support for the view that age-related DA losses are associated with age-related cognitive deficits. Future research strategies for examining the DA-cognitive aging link include assessing (a) the generality/specificity of the effects; (b) the relationship between neuromodulation and functional brain activation; and (c) the release of DA during actual task performance.

Aging↗
PubMed2006

Dual-tasking postural control: aging and the effects of cognitive demand in conjunction with focus of attention.

Postural control in everyday life is generally accompanied by posture-unrelated cognitive activity. Thus, mild forms of dual-tasking postural control are the norm rather than the exception. Based on this consideration and available evidence, we propose and empirically examined, in young and old adults, a non-monotonic, U-shaped relation between the efficacy of postural control and concurrent cognitive demands that reflect opposing trends of the effects of attention focus and attentional resource competition. When instructed to perform an easy cognitive task that presumably shifted the focus of attention away from posture control, the center of body pressure (COP) excursions decreased both in young and older adults relative to a single-task baseline where the focus of attention was explicitly directed towards the postural control task itself. However, when performing more demanding cognitive tasks, older adults showed increased COP displacements, in line with the predicted U-shape function, whereas young adults did not. We outline mechanisms linking postural control to cognitive demand and suggest routes for future investigation.

Adult↗
PubMed2006

Prediction of the prognosis in patients with acute-on-chronic hepatitis using the MELD scoring system.

AIM: To predict prognosis in patients with acute-on-chronic hepatitis (AOCH) using the model for end-stage liver disease (MELD) scoring system and to study the effects of age, sex, etiology, low serum sodium, and persistent ascites on MELD. METHODS: The MELD scores of 300 patients with AOCH were calculated according to the original formula. The 3-month mortality in patients was measured, and the validity of the models was determined by means of the concordance (c) statistic. The influential factors on MELD were also assessed. RESULTS: The 3-month mortality of AOCH patients with a MELD score of 20-29 was 56.0%, with a score of 30-39 it was 76.5%, and with a score over 40 it was 98.2%. The concordance (c) statistic of 3-month mortality was 0.782. Univariate analysis showed that mortality was significantly related to age (P=0.047), etiology (P=0.039), serum sodium (P=0.029) and ascites (P=0.031) for patients with MELD scores 20-29. In multivariate analysis, in patients with MELD scores 20-29, age (P=0.012), etiology (P=0.024), serum sodium (P=0.005) and ascites (P=0.017) were independent predictors of mortality; for MELD scores above 30, only MELD score (P=0.015) was independently predictive. CONCLUSIONS: The MELD scoring system is a reliable method for predicting mortality in patients with AOCH. In the group with MELD score 20-29, factors including age, etiology, presence of low serum sodium and persistent ascites may influence the MELD scoring system. The MELD score is the decisive predictor of the prognosis of patients with AOCH when the MELD score is over 30.

Adult↗
PubMed2005

Aging neuromodulation impairs associative binding: a neurocomputational account.

Relative to young adults, older adults are particularly impaired in episodic memory tasks requiring associative binding of separate components into compound episodes, such as tasks requiring item-context and item-item binding. This associative-binding deficit has been attributed to senescent changes in frontal-hippocampal circuitry but has not been formally linked to impaired neuromodulation involving this circuitry. Previous neurocomputational work showed that impaired neuromodulation could result in less distinct neurocognitive representations. Here we extend this computational principle to simulate aging-related deficits in associative binding. As expected, networks with simulated deficiency in neuromodulation resulted in less distinct internal representations than did networks simulating the processing and performance of young adults, and were also more impaired under task conditions that required associative binding. The findings suggest that senescent changes in neuromodulatory mechanisms may play a basic role in aging-related impairment in associative binding by reducing the efficacy of distributed conjunctive coding.

Aged↗
PubMed2004

Visual search across the life span.

Gains and losses in visual search were studied across the life span in a representative sample of 298 individuals from 6 to 89 years of age. Participants searched for single-feature and conjunction targets of high or low eccentricity. Search was substantially slowed early and late in life, age gradients were more pronounced in conjunction than in feature search, and all age groups were uniformly affected by eccentricity manipulations. However, developmental and aging trends were distinctly asymmetrical: Children's performance was particularly affected by the mere presence of distractors; whereas in late life, performance was particularly impaired on target-absent trials and with increasing numbers of distractors. The implications for life span theories of cognitive and attentional development and for cognitive-speed and inhibitory-control accounts are discussed.

Adolescent↗
PubMed2004

Toward an alternative representation for disentangling age-associated differences in general and specific cognitive abilities.

Much of cognitive aging research concerns whether age-associated differences in various cognitive performances can be accounted for by general explanatory constructs or whether several specific processes are involved. Structural equation models have been proposed to disentangle general and specific age-associated differences in cognitive performance. This article demonstrates that existing methods that employ stepwise procedures run the risk of biasing results toward general resource accounts. An alternative model representation (i.e., the nested factor model) is proposed that affords simultaneous estimation of general and specific effects and is applied to data from the Berlin Aging Study. Using the nested factor model allowed the authors to detect that specific group factors explained 25% of the age-associated variance in addition to the general factor.

Adult↗
PubMed2004

Transformations in the couplings among intellectual abilities and constituent cognitive processes across the life span.

Two-component theories of intellectual development over the life span postulate that fluid abilities develop earlier during child development and decline earlier during aging than crystallized abilities do, and that fluid abilities support or constrain the acquisition and expression of crystallized abilities. Thus, maturation and senescence compress the structure of intelligence by imposing age-specific constraints upon its constituent processes. Hence, the couplings among different intellectual abilities and cognitive processes are expected to be strong in childhood and old age. Findings from a population-based study of 291 individuals aged 6 to 89 years support these predictions. Furthermore, processing robustness, a frequently overlooked aspect of processing, predicted fluid intelligence beyond processing speed in old age but not in childhood, suggesting that the causes of more compressed functional organization of intelligence differ between maturation and senescence. Research on developmental changes in functional brain circuitry may profit from explicitly recognizing transformations in the organization of intellectual abilities and their underlying cognitive processes across the life span.

Adolescent↗
PubMed2003

Biocultural orchestration of developmental plasticity across levels: the interplay of biology and culture in shaping the mind and behavior across the life span.

The author reviews reemerging coconstructive conceptions of development and recent empirical findings of developmental plasticity at different levels spanning several fields of developmental and life sciences. A cross-level dynamic biocultural coconstructive framework is endorsed to understand cognitive and behavioral development across the life span. This framework integrates main conceptions of earlier views into a unifying frame, viewing the dynamics of life span development as occurring simultaneously within different time scales (i.e., moment-to-moment microgenesis, life span ontogeny, and human phylogeny) and encompassing multiple levels (i.e., neurobiological, cognitive, behavioral, and sociocultural). Viewed through this metatheoretical framework, new insights of potential interfaces for reciprocal cultural and experiential influences to be integrated with behavioral genetics and cognitive neuroscience research can be more easily prescribed.

Aging↗
PubMed2002

Integrative neurocomputational perspectives on cognitive aging, neuromodulation, and representation.

Besides neuroanatomical changes, neuromodulatory mechanisms are also compromised during aging. Neural network models are suitable tools for exploring the relatively broad and homogenous neuromodulatory influences on cortical function. Computational approaches for understanding neuromodulation of the dynamic properties of cortical function and recent neurocomputational theories relating different aspects of cognitive aging with declines in neuromodulation are reviewed. Considered within an integrative cross-level neurocomputational framework, aging-related decline in dopaminergic neuromodulation reduces the fidelity of neural information and gives rise to less distinctive neural pattern representations that may underlie various facets of aging cognitive and, possibly also, sensorimotor phenomena.

Aging↗
PubMedDate not supplied

Age is not necessarily aging: another step towards understanding the "clocks" that time aging.

Hofer and Sliwinski raise a critical concern regarding a popular practice in aging research of inferring associations among aging changes of different processes from correlations based on cross-sectional age differences. It is shown analytically that cross-sectional information drawn from age-heterogeneous samples is not suitable for answering questions about the interdependence between aging changes. While in general we agree with the problem pointed out by Hofer and Sliwinski, the two aims of this commentary are: (1) to highlight links between the specific concern and two long-standing issues confronting life-span researchers and (2) to introduce alternative approaches that are currently underutilized in gerontological research. We elaborate general issues with respect to challenges in inferring aging changes from age differences and using age as a proxy for aging. We show that several other sources of variance independent of rates of change, such as cohort- and mortality-related selection effects, are confounded in age-heterogeneous designs. We suggest general considerations for developing more explicit theories of cognitive aging in the future. Alternative research methods and paradigms for studying the causes and mechanisms of the aging mind at different time scales and levels are also highlighted. The role of chronological age in aging research is rather "superficial". To understand the underlying processes and mechanisms of cognitive aging, classical process-oriented, rather than solely age-oriented, theoretical conceptions need to be reconsidered and reified with new methodological and empirical advances. Concerted gerontological research endeavors utilizing recent progresses made in statistical analyses of dynamic processes and in cognitive and computational neurosciences that may lead to fruitful breakthroughs.

Aged↗
PubMedDate not supplied

Aging and attenuated processing robustness. Evidence from cognitive and sensorimotor functioning.

BACKGROUND: Within-person, across-time variations in processes and performance are intrinsic to all aspects of human functioning. OBJECTIVE: This article starts with a brief taxonomy of intraindividual dynamics. There are adaptive as well as non-adaptive types of intraindividual variations that unfold with different degrees of reversibility on different time scales and involve either single, or systems of, functions. METHODS: Empirical findings regarding aging and a specific type of intraindividual variation, namely attenuated processing robustness, are then presented with respect to cognitive and sensorimotor functioning. RESULTS: In both domains of functioning, old adults exhibit less robust functioning with a greater amount of week-to-week, day-to-day, or trial-by-trial fluctuations in their cognitive, walking, and postural control performances. CONCLUSION: Currently, the causes for the attenuation of processing robustness in cognitive and sensorimotor functioning are not well understood. Neurocomputational models are useful tools for exploring the tripartite relationships between the aging of neural information-processing fidelity, and cognitive, and sensorimotor processes.

Aging↗