Working memory in Down syndrome: is there a dual task deficit?

BACKGROUND: Recent studies have shown that individuals with Down syndrome (DS) are poorer than controls in performing verbal and visuospatial dual tasks. The present study aims at better investigating the dual task deficit in working memory in individuals with DS. METHOD: Forty-five individuals with DS and 45 typically developing children matched for verbal mental age completed a series of verbal and visuospatial working memory tasks, involving conditions that either required the combination of two tasks in the same modality (verbal or visual) or of cross-modality pairs of tasks. RESULTS AND CONCLUSIONS: Two distinct deficits were found in individuals with DS: impairment in verbal tasks and further impairment in all dual task conditions. The results confirm the hypothesis of a central executive impairment in individuals with DS.

TB preventive treatment among pregnant women with HIV.

BACKGROUND: The WHO recommends TB preventive treatment (TPT) for people living with HIV, including pregnant women. Uptake of this policy recommendation in this subpopulation and country alignment with WHO guidance is unclear.METHODS: We conducted a policy review in 38 WHO high TB and TB-HIV burden countries to assess if the uptake of TPT policy among pregnant women living with HIV was in line with the WHO´s 2018 Updated and Consolidated Guidelines for Programmatic Management for LTBI. Data sources included TB national guidelines and HIV/AIDS/ART national guidelines, complemented by results from a previous survey on policy uptake held at the WHO.RESULTS: Uptake of WHO policy to provide TB preventive treatment among women with HIV accessing antenatal care was moderate: 64% (23 of 36 countries) explicitly recommended at least one clinical guideline or policy recommendation on screening, testing or treatment of LTBI among pregnant women living with HIV. There was considerable variation between countries on the stages in pregnancy that TPT should be provided. Two countries (5%) provided clinical monitoring recommendations for pregnant women.CONCLUSIONS: There is moderate uptake of TPT policy for pregnant women with HIV. Failure to provide TPT as part of antenatal or prevention of mother-to-child services is a missed opportunity for TB control.

Working memory.

The term working memory refers to a brain system that provides temporary storage and manipulation of the information necessary for such complex cognitive tasks as language comprehension, learning, and reasoning. This definition has evolved from the concept of a unitary short-term memory system. Working memory has been found to require the simultaneous storage and processing of information. It can be divided into the following three subcomponents: (i) the central executive, which is assumed to be an attentional-controlling system, is important in skills such as chess playing and is particularly susceptible to the effects of Alzheimer's disease; and two slave systems, namely (ii) the visuospatial sketch pad, which manipulates visual images and (iii) the phonological loop, which stores and rehearses speech-based information and is necessary for the acquisition of both native and second-language vocabulary.

Recent developments in working memory.

Research on the visual and verbal subsystems of working memory has shown vigorous development, with PET, fMRI and behavioral data all supporting separate systems, with further fractionation being likely. Analysis of executive processes is revealing a range of subprocesses, providing a very fruitful field for the interaction of cognitive psychology, neuropsychology and functional imaging.

The multi-component model of working memory: explorations in experimental cognitive psychology.

There are a number of ways one can hope to describe and explain cognitive abilities, each of them contributing a unique and valuable perspective. Cognitive psychology tries to develop and test functional accounts of cognitive systems that explain the capacities and properties of cognitive abilities as revealed by empirical data gathered by a range of behavioral experimental paradigms. Much of the research in the cognitive psychology of working memory has been strongly influenced by the multi-component model of working memory [Baddeley AD, Hitch GJ (1974) Working memory. In: Recent advances in learning and motivation, Vol. 8 (Bower GA, ed), pp 47-90. New York: Academic Press; Baddeley AD (1986) Working memory. Oxford, UK: Clarendon Press; Baddeley A. Working memory: Thought and action. Oxford: Oxford University Press, in press]. By expanding the notion of a passive short-term memory to an active system that provides the basis for complex cognitive abilities, the model has opened up numerous questions and new lines of research. In this paper we present the current revision of the multi-component model that encompasses a central executive, two unimodal storage systems: a phonological loop and a visuospatial sketchpad, and a further component, a multimodal store capable of integrating information into unitary episodic representations, termed episodic buffer. We review recent empirical data within experimental cognitive psychology that has shaped the development of the multicomponent model and the understanding of the capacities and properties of working memory. Research based largely on dual-task experimental designs and on neuropsychological evidence has yielded valuable information about the fractionation of working memory into independent stores and processes, the nature of representations in individual stores, the mechanisms of their maintenance and manipulation, the way the components of working memory relate to each other, and the role they play in other cognitive abilities. With many questions still open and new issues emerging, we believe that the multicomponent model will continue to stimulate research while providing a comprehensive functional description of working memory.

Symmetry and binding in visuo-spatial working memory.

Three experiments study the impact of symmetry on a sequential block tapping immediate memory task in human subjects. Experiment 1 shows an advantage from vertical symmetry over non-symmetrical sequences, while finding no effect of horizontal or diagonal symmetry. Experiment 2 tests the possible role of verbal labeling by means of a secondary task that prevents this by articulatory suppression. No evidence of verbalization was observed. A third study examines the effects of a concurrent executive load, finding an overall impairment, that did not differ between symmetrical and asymmetric patterns, suggesting that the effect of symmetry reflects automatic rather than executive processes. Implications for the episodic buffer component of working memory are discussed.

When implicit learning fails: amnesia and the problem of error elimination.

We propose that one of the major functions of explicit memory is the elimination of learning errors. The hypothesis is explored by means of a stem completion task in which subjects are presented with stems having many potential completions, and in the initial phase are either encouraged to guess, the "errorful" procedure, or are provided with the correct completion, the "errorless" condition. Learning is then tested over a sequence of nine trials. The performance of amnesic subjects who are assumed to have good implicit but bad explicit learning is compared with that of normal elderly subjects, who are assumed to have an intermediate level of explicit learning skill, and young controls who are expected to be high in both implicit and explicit learning capacity. As predicted, errorless learning is beneficial, with the effect being particularly marked for the amnesic group. A detailed analysis of the intrusion errors supports an interpretation of the results in terms of the relative contribution to the three groups of implicit learning, which is assumed to be particularly vulnerable to interference. Implications for the analysis of normal learning, and for the rehabilitation of brain damaged patients are discussed.

Genetically dissociated components of working memory: evidence from Down's and Williams syndrome.

Wang and Bellugi [J clin exp Neuropsychol 1994;16:317 22] have suggested that Down's and Williams syndrome might be associated with specific and contrasting working memory deficits; with impaired verbal short-term memory in Down's syndrome, and a visuo-spatial short-term memory deficit in Williams syndrome. In two studies we examine whether these apparent deficits might simply be a consequence of the general pattern of learning difficulties associated with these disorders. Experiment 1 compared verbal and visuo-spatial short-term memory abilities in these groups, using analysis of covariance to control for mental age differences. In Experiment 2 individuals with Williams syndrome were matched to control groups for non-verbal mental age, and the short-term memory abilities of these matched groups were compared. The results of both experiments are broadly consistent with those reported by Wang and Bellugi, and support the view that working memory can be dissociated into separate subsystems.

Memory in schizophrenia: what is impaired and what is preserved?

This study assesses the pattern of long-term memory performance in a sample of 12 schizophrenic patients who were selected on the basis of showing a memory deficit in the absence of gross overall intellectual impairment. When compared with 12 control subjects matched for age, sex and estimated premorbid IQ, presence of an episodic memory deficit was confirmed for both prose recall and forced-choice word and face recognition. Semantic memory was assessed using the sentence verification task developed by Collins and Quillian, an unpaced category judgement task, and the Mill Hill Vocabulary Scale. The schizophrenic patients were slower on sentence verification and they made significantly more errors in all three tasks. Procedural tasks included pursuit rotor performance, speed of repeatedly assembling a jigsaw puzzle and rate of improvement in reading transformed script. Here, while the schizophrenic patients showed poor overall performance on the pursuit rotor and jigsaw learning, their rate of learning on all three procedural tasks was comparable with that of the controls. When examined on two implicit memory tasks involving biasing of spelling of homophones and word stem completion, the patients showed a normal degree of priming in both. Implications for the nature of the memory deficit in schizophrenia are discussed.

Analysis of the episodic memory deficit in early Alzheimer's disease: evidence from the doors and people test.

Anterograde episodic memory was assessed in a cohort of 33 patients with early dementia of Alzheimer type (DAT) and 30 matched controls using immediate and delayed prose recall, the CERAD word learning test and the recently developed doors and people test of visual and verbal recall and recognition. DAT patients showed markedly impaired learning on all three measures, with little evidence of cumulation of information across trials. Patients showed more forgetting than controls on prose recall and the CERAD word list, but more detailed analysis suggested that this differential loss was attributable to the contribution of primary memory to immediate but not delayed recall. No differences in forgetting rate were observed on the doors and people test. Scaled scores were used to derive a recall-recognition index, together with a measure of material-specific memory based on the ratio of verbal to visual memory deficits. There was no evidence for differential sensitivity of recall over recognition, implying that the episodic memory deficit is one of learning, rather than of the retrieval of learned material. Although individuals varied in the relative degree of impairment of verbal and visual memory, there was no general tendency for material-specificity. It was concluded that the episodic memory deficit in DAT is general in nature and primarily reflects impaired learning rather than accelerated forgetting or disrupted retrieval.

Autobiographical memory and executive function in early dementia of Alzheimer type.

We studied executive function and autobiographical memory in a cohort of 33 DAT patients [divided into minimal (MMSE 24-30) and mild (MMSE 17-23) groups] and in 30 normal controls. Autobiographical memory, as assessed by autobiographical fluency and the Autobiographical Memory Interview (AMI), was impaired in DAT patients, even those with minimal disease. There was evidence of a gentle temporal gradient on the incident but not the personal semantic component of the AMI, suggesting that the two components are dissociable. Executive function was assessed by two separate dual performance tasks and letter fluency. Although there was a trend for minimal DAT patients to be impaired on executive tasks, this only reached significance for the mild group. Regression analysis suggested that the divided attention component of working memory was involved in the retrieval of personal semantic autobiographical memory, but verbal fluency was more important in the retrieval of autobiographical incidents. There was thus a dissociation in the type of executive function implicated in different subcomponents of autobiographical memory, arguing for subcomponents within executive function and autobiographical memory. The autobiographical memory deficit in DAT reflects, we argue, both impairment in retrieval processes, linked to executive function, and a loss of memory stores.

Pattern span: a tool for unwelding visuo-spatial memory.

Evidence showing that non-verbal short-term memory has distinct visual and spatial/sequential components is reviewed. A new test, The Visual Patterns Test (VPT), which was designed to measure short-term visual memory largely shorn of its spatio-sequential component, is described. Correlational studies of the VPT and the Corsi Blocks Test with healthy subjects and brain-damaged patients indicate a separation between visual and sequential abilities. This separation of function is supported by double dissociations shown by patients. Moreover, in a selective interference experiment, the VPT and the Corsi tests were found to show a double dissociation pattern of interference from visual and spatio sequential subsidiary tasks, respectively. The present results are discussed in relation to other findings in the literature, and it is concluded that non-verbal short-term memory can indeed be viewed as comprising distinct visual and spatio-sequential components. The VPT will be a useful neuropsychological instrument for measuring the visual component.

The phonological loop as a language learning device.

A relatively simple model of the phonological loop (A. D. Baddeley, 1986), a component of working memory, has proved capable of accommodating a great deal of experimental evidence from normal adult participants, children, and neuropsychological patients. Until recently, however, the role of this subsystem in everyday cognitive activities was unclear. In this article the authors review studies of word learning by normal adults and children, neuropsychological patients, and special developmental populations, which provide evidence that the phonological loop plays a crucial role in learning the novel phonological forms of new words. The authors propose that the primary purpose for which the phonological loop evolved is to store unfamiliar sound patterns while more permanent memory records are being constructed. Its use in retaining sequences of familiar words is, it is argued, secondary.

Working memory and the vividness of imagery.

The working memory framework was used to investigate the factors determining the phenomenological vividness of images. Participants rated the vividness of visual or auditory images under control conditions or while performing tasks that differentially disrupted the visuospatial sketchpad and phonological loop subsystems of working memory. In Experiments 1, 2, and 6, participants imaged recently presented novel visual patterns and sequences of tones; ratings of vividness showed the predicted interaction between stimulus modality and concurrent task. The images in experiments 3, 4, 5, and 6 were based on long-term memory (LTM). They also showed an image modality by task interaction, with a clear effect of LTM variables (meaningfulness, activity, bizarreness, and stimulus familiarity), implicating both working memory and LTM in the experience of vividness.

Working memory and the control of action: evidence from task switching.

A series of 7 experiments used dual-task methodology to investigate the role of working memory in the operation of a simple action-control plan or program involving regular switching between addition and subtraction. Lists requiring switching were slower than blocked lists and showed 2 concurrent task effects. Demanding executive tasks impaired performance on both blocked and switched lists, whereas articulatory suppression impaired principally the switched condition. Implications for models of task switching and working memory and for the Vygotskian concept of verbal control of action are discussed.

The risk of MDR-TB and polyresistant tuberculosis among the civilian population of Tomsk city, Siberia, 1999.

SETTING: Tomsk, Siberia, Russian Federation. OBJECTIVE: To evaluate the relationship between TB susceptibility patterns and risk factors among a civilian cohort of new cases in Tomsk city in 1999. DESIGN: Population-based study. The association between MDR-TB or PROMDR-TB, defined as resistance to isoniazid and rifampicin (MDR) or to isoniazid, ethambutol, and streptomycin (rifampicin mono-sensitive), and hypothesized risk factors was determined. Univariable analysis with and without stratification for history of incarceration and stepwise logistic regression modeling were used. RESULTS: Overall, 49.6% of participants were infected with a Mycobacterium tuberculosis strain resistant to at least one prescribed anti-tuberculosis medication. PROMDR-TB and MDR-TB were prevalent in 17.2% and 13.1% of participants, respectively. Logistic regression modeling indicated that good residence (OR 3.1, 95%CI 1.4-6.9), treatment default (OR 4.4, 95%CI 2.1-9.3) and psychological disorder (OR 3.3, 95%CI 1.0-10.9) were associated with PROMDR-TB. Both good residence (OR 2.6, 95%CI 1.1-6.0) and treatment default (OR 5.3, 95%CI 2.4-11.6) were associated with MDR-TB. History of incarceration was not found to be significant. CONCLUSION: Our findings support the hypothesis that drug-resistant disease among the Tomsk city population is not directly linked to history of incarceration, nor is it an extension of drug resistance in prisons. Rather, drug resistance in the civil sector reflects problems specific to the sector itself.

Dual-task performance in dysexecutive and nondysexecutive patients with a frontal lesion.

Patients with defined frontal lobe lesions were assigned to 1 of 2 groups based on whether they showed a behaviorally assessed dysexecutive syndrome or were behaviorally normal. All participants were tested on dual-task performance and on 2 tasks assumed to measure frontal lobe function, the Wisconsin Card Sorting Test and verbal fluency. The dysexecutive group differed significantly from the nondysexecutive in showing impaired capacity for dual-task coordination, but there were no significant differences on the Wisconsin Card Sorting Test and verbal fluency. Results are interpreted in terms of a multicomponent central executive, whose function is linked to, but not coterminous with, the operation of the frontal lobes.

Confabulation in a dysexecutive patient: implication for models of retrieval.

A confabulating patient MM is described who, despite clear evidence of a dysexecutive syndrome, showed normal prospective and retrospective memory in everyday life and preserved autobiographical memory. He also performed well on many, but not all laboratory-based measures of learning and memory that were given. His confabulation typically involved going well-beyond the information he could genuinely recall, and was attributed to a defect in memory monitoring resulting from his frontal lobe damage. Implications for the role of "stop rules" in memory retrieval are discussed.

A case of word deafness with preserved span: implications for the structure and function of short-term memory.

Case IJ shows impaired capacity to repeat individual words despite normal hearing as measured by audiometry and tympanometry. She also has difficulty in identifying other environmental sounds. Her phonological memory span for visually-presented material is normal, and her memory span for spoken digits is only slightly impaired. It is suggested that she has a pre-phonological auditory processing deficit; the implications of this for discussion of the role of phonological short-term memory in language processing are discussed.