Effects of Aging on Sleep-Dependent Consolidation of Declarative Memory

Sleep plays a critical role in memory consolidation. However, aging is associated with changes in sleep architecture and memory impairments. The goal of the present study was to identify age-related changes in the memory function of sleep by investigating sleep-dependent changes in neural activation patterns during memory retrieval in young and older adults. Healthy young (21-29 years) and older (62-74 years) adults were trained on a declarative word-pair learning task. Recall was tested 5 hr later while undergoing functional magnetic resonance imaging (fMRI). Participants completed this testing procedure twice, separated by 1 week; once following a mid-day nap and once following continuous wakefulness in a counter-balanced order. Sleep was recorded by polysomnography for the naps and subsequent nocturnal intervals. It was found that napping, as compared to wakefulness, was associated with decreased hippocampal activation and decreased hippocampo-frontal co-activation in young adults. Specifically, slow wave sleep (SWS) in the young adult naps was associated with better memory retention (r = .61, p = .035) and decreased hippocampal activation (r = -.71, p = .01) lending support to the two-stage model of memory consolidation (McClelland, McNaughton & O’Reilly, 1995). On the other hand, sleep-dependent neural reorganization patterns were different in the older adult group. Following a nap, retrieval still required hippocampal activation and hippocampo-frontal co-activation (adjusted R2 = .701, F(1,10) = 22.08, p = .002). Furthermore, in contrast to a SWS-dependent decrease in anterior cingulate cortex (ACC) activation in young adults for successful retrieval (r = -.61, p = .037), ACC activation in older adults was increased when retrieval was tested following a nap compared to wakefulness, and was not significantly associated with measures of SWS. This suggests that successful retrieval following a nap required allocation of error monitoring processes in older adults. In summary, the present study shows that the efficiency with which systems level consolidation takes place in the first sleep opportunity following learning of a declarative memory task changes in healthy aging. Slow wave sleep-dependent reactivation processes may be disrupted, leaving memory traces at a more labile state of storage that requires additional allocation of cognitive control processes

Failure to mobilize cognitive control for challenging tasks correlates with symptom severity in schizophrenia

Deficits in the adaptive, flexible control of behavior contribute to the clinical manifestations of schizophrenia. We used functional MRI and an antisaccade paradigm to examine the neural correlates of cognitive control deficits and their relations to symptom severity. Thirty-three chronic medicated outpatients with schizophrenia and 31 healthy controls performed an antisaccade paradigm. We examined differences in recruitment of the cognitive control network and task performance for Hard (high control) versus Easy (low control) antisaccade trials within and between groups. We focused on the key regions involved in ‘top-down’ control of ocular motor structures – dorsal anterior cingulate cortex, dorsolateral and ventrolateral prefrontal cortex. In patients, we examined whether difficulty implementing cognitive control correlated with symptom severity. Patients made more errors overall, and had shorter saccadic latencies than controls on correct Hard vs. Easy trials. Unlike controls, patients failed to increase activation in the cognitive control network for Hard vs. Easy trials. Reduced activation for Hard vs. Easy trials predicted higher error rates in both groups and increased symptom severity in schizophrenia. These findings suggest that patients with schizophrenia are impaired in mobilizing cognitive control when presented with challenges and that this contributes to deficits suppressing prepotent but contextually inappropriate responses, to behavior that is stimulus-bound and error-prone rather than flexibly guided by context, and to symptom expression. Therapies aimed at increasing cognitive control may improve both cognitive flexibility and reduce the impact of symptoms

Spared and impaired sleep-dependent memory consolidation in schizophrenia

Objective: Cognitive deficits in schizophrenia are the strongest predictor of disability and effective treatment is lacking. This reflects our limited mechanistic understanding and consequent lack of treatment targets. In schizophrenia, impaired sleep-dependent memory consolidation correlates with reduced sleep spindle activity, suggesting sleep spindles as a potentially treatable mechanism. In the present study we investigated whether sleep-dependent memory consolidation deficits in schizophrenia are selective. Methods: Schizophrenia patients and healthy individuals performed three tasks that have been shown to undergo sleep-dependent consolidation: the Word Pair Task (verbal declarative memory), the Visual Discrimination Task (visuoperceptual procedural memory), and the Tone Task (statistical learning). Memory consolidation was tested 24h later, after a night of sleep. Results: Compared with controls, schizophrenia patients showed reduced overnight consolidation of word pair learning. In contrast, both groups showed similar significant overnight consolidation of visuoperceptual procedural memory. Neither group showed overnight consolidation of statistical learning. Conclusion: The present findings extend the known deficits in sleep-dependent memory consolidation in schizophrenia to verbal declarative memory, a core, disabling cognitive deficit. In contrast, visuoperceptual procedural memory was spared. These findings support the hypothesis that sleep-dependent memory consolidation deficits in schizophrenia are selective, possibly limited to tasks that rely on spindles. These findings reinforce the importance of deficient sleep-dependent memory consolidation among the cognitive deficits of schizophrenia and suggest sleep physiology as a potentially treatable mechanism

Sleep-dependent consolidation of value-based learning.

It has been suggested that sleep selectively enhances memories with future relevance. Given that sleep's benefits can vary by item within a learning context, the present study investigated whether the amount of sleep-dependent consolidation may vary across items based on the value of the to-be-learned material. For this purpose, we used a value-based learning paradigm in which participants studied words paired with point values. There were two groups; participants either studied the words in the evening and were tested after a 12 hr interval containing a full night of sleep, or studied the words in the morning and were tested after 12 hr of continuous daytime wake. Free recall (F(1,36) = 19.35, p<.001) and recognition accuracy (F(1,36) = 7.59, p = .01) for words were better following sleep relative to wake. However there was no difference in the linear increase in the probability of delayed recall with increasing word value for sleep and wake groups (p = .74). Thus, while encoding may vary with the value of the to-be-learned item, sleep-dependent consolidation does not

Episodic Memory and Metamemory in Parkinson's Disease Patients

This study investigated episodic memory and metamemory for verbs and nouns in patients who have cognitive impairments associated with Parkinson's disease (PD). PD patients and healthy control participants were asked to recall word pairs and provide feeling-of-knowing (FOK) judgments for the items they were unable to recall. This was followed by a 4-alternative recognition test. PD patients were impaired in both recall and recognition, compared with controls. In terms of metamemory, PD patients were less confident in their ability to recognize the unrecalled items in a future recognition test. Most important, accuracy of PD patients' FOK judgments was not above chance and was lower than that of control participants. The PD group correctly recognized fewer verbs than nouns, but type of material (verb vs. noun) had no impact on recall or FOK judgments. In addition, contribution of executive functions to FOK accuracy was different in PD patients and controls

Supplemental Material - Co-axial electrospinning of PLLA shell, collagen core nanofibers for skin tissue engineering

Supplemental Material for Co-axial electrospinning of PLLA shell, collagen core nanofibers for skin tissue engineering by Erkan T Baran, Aydin Tahmasebifar and Bengi Yilmaz in Journal of Biomaterials Applications</p

Surface modification strategies for hemodialysis catheters to preventcatheter-relatedinfections: A review

Yilmaz, Bengi/0000-0001-7642-4684WOS: 000564023400001PubMed: 32864803Insertion of a central venous catheter is one of the most common invasive procedures applied in hemodialysis therapy for end-stage renal disease. the most important complication of a central venous catheter is catheter-related infections that increase hospitalization and duration of intensive care unit stay, cost of treatment, mortality, and morbidity rates. Pathogenic microorganisms, such as, bacteria and fungi, enter the body from the catheter insertion site and the surface of the catheter can become colonized. the exopolysaccharide-based biofilms from bacterial colonies on the surface are the main challenge in the treatment of infections. Catheter lock solutions and systemic antibiotic treatment, which are commonly used in the treatment of hemodialysis catheter-related infections, are insufficient to prevent and terminate the infections and eventually the catheter needs to be replaced. the inadequacy of these approaches in termination and prevention of infection revealed the necessity of coating of hemodialysis catheters with bactericidal and/or antiadhesive agents. Silver compounds and nanoparticles, anticoagulants (e.g., heparin), antibiotics (e.g., gentamicin and chlorhexidine) are some of the agents used for this purpose. the effectiveness of few commercial hemodialysis catheters that were coated with antibacterial agents has been tested in clinical trials against catheter-related infections of pathogenic bacteria, such asStaphylococcus aureusandStaphylococcus epidermidiswith promising results. Novel biomedical materials and engineering techniques, such as, surface micro/nano patterning and the conjugation of antimicrobial peptides, enzymes, metallic cations, and hydrophilic polymers (e.g., poly [ethylene glycol]) on the surface, has been suggested recently

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Ankara : İhsan Doğramacı Bilkent Üniversitesi İktisadi, İdari ve Sosyal Bilimler Fakültesi, Tarih Bölümü, 2017.This work is a student project of the The Department of History, Faculty of Economics, Administrative and Social Sciences, İhsan Doğramacı Bilkent University.by Emiroğlu, Kudret