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PubMed2000

Brain dynamics in theta and alpha frequency bands and working memory performance in humans.

In this study non-linear and linear global electroencephalogram (EEG) changes during a visual working memory task were studied using a separate analysis of theta, lower alpha and upper alpha band filtered data. EEGs were recorded in 21 healthy subjects (62.5 year; SD 2.1; 12 females, nine males) during an eyes-closed no-task condition and a working memory condition. Coarse-grained dimension was estimated for both conditions from spatially embedded EEG data filtered in the theta band and both alpha bands. Linear measures of coupling and mean amplitude were also computed. During the working memory condition lower alpha band dimension increased. Linear analysis showed alpha1 band desynchronization. Female subjects had a higher dimension in the theta band as well as more desynchronization in the theta and alpha1 band. Working memory capacity correlated with a lower theta band dimension during the no-task condition in female subjects. The increase in alpha1 band complexity can be interpreted as increased desynchronization corresponding with attentional processes. Higher complexity/desynchronization in females seems to be a more structural phenomenon and may be more intimately related to task performance.

Alpha Rhythm↗
PubMed1993

Effects of p-chlorophenylalanine and methysergide on the performance of a working memory task.

The present study investigated the effects of serotonergic dysfunction on working memory. Therefore, the effects of inhibition of serotonin [5-hydroxytryptamine (5-HT)] synthesis induced by p-chlorophenylalanine (p-CPA) and pharmacological blockade of 5-HT receptors by methysergide on the performance of rats in a delayed nonmatching to position task assessing spatial working memory were studied. Methysergide (1.0, 5.0, or 15.0 mg/kg) significantly disrupted behavioral activity of rats and decreased the percent correct total responses. However, the impairment in the percent correct responses was delay independent, indicating a nonmnemonic disruption of the performance. p-CPA (500 mg/kg/day x 3) induced an almost total depletion (> 97%) of frontal cortical and hippocampal serotonin and its major metabolite 5-hydroxyindoleacetic acid and slightly affected noradrenergic and dopaminergic systems. p-CPA treatment did not affect the percent correct responses. However, the behavioral activity of rats was slightly decreased by p-CPA. The disruptions in behavioral activity and the percent correct responses induced by methysergide (2.0 mg/kg) were not abolished by p-CPA. The present results do not support any important role for the serotonergic system in spatial working memory as assessed using the delayed nonmatching to position task.

Animals↗
PubMed1997

Is working memory intact in alcoholics? An ERP study.

Few investigators have applied the working memory theory to studies on abstinent chronic alcoholics, though it has been reported that the deficits in short-term memory appear to be specific to visuo-spatial and problem-solving tasks. In the present study, we recorded ERPs from 40 male control subjects and 78 alcoholics performing a modified delayed matching to sample task. To minimize the possible confound of retinotopic projections for the matching stimuli, in contrast to the non-matching stimuli, we employed a unique set of stimuli in our delayed matching to sample task. Our results indicate that an ERP component, occurring at approximately 250 ms post-stimulus, may be a reflection of the ERP mnemonic effect for working memory. This component distinguishes the two groups at the right occipitotemporal region, providing evidence of right hemisphere dysfunction in alcoholics. Thus, the current experiment may show electrophysiological evidence of working memory deficits in alcoholics.

Adult↗
PubMed1995

Visuo-spatial working memory: structures and variables affecting a capacity measure.

The present paper examines the issue of the capacity of visuo-spatial working memory. A series of experiments test the hypothesis that two different components are critical in visuo-spatial working memory (passive store and active imagery operations), and, thereafter, attempt to specify the variables that affect the capacity of the passive store component. In the experiments, congenitally blind and sighted participants were asked to remember the spatial positions of target objects in two-dimensional matrices, with or without simultaneously performing a sequence of spatially-based imagery operations. We considered both the positions recall performance (the passive storage component) and the sequential imagery processing performance (the active processing component). We suggest that the two components of visuo-spatial working memory are independent. We also propose that both the number of relevant matrices and the number of target objects within each matrix affect the capacity of visuo-spatial working memory, with the latter factor possibly playing a greater role than the former one.

Adult↗
PubMed2005

The role of working memory in attentional capture.

Much previous research has demonstrated that visual search is typically disrupted by the presence of a unique "singleton" distractor in the search display. Here we show that attentional capture by an irrelevant color singleton during shape search critically depends on availability of working memory to the search task: When working memory is loaded in a concurrent yet unrelated verbal short-term memory task, capture increases. These findings converge with previous demonstrations that increasing working memory load results in greater distractor interference in Stroop-like tasks (de Fockert, Rees, Frith, & Lavie, 2001; Lavie, Hirst, de Fockert, & Viding, 2004), which support the hypothesis that working memory provides goal-directed control of visual selective attention allowing to minimize interference by goal-irrelevant distractors.

Attention↗
PubMed2005

Dorsolateral prefrontal cortex activity during maintenance and manipulation of information in working memory in patients with schizophrenia.

CONTEXT: It remains unclear whether altered regional brain physiological activity in patients with schizophrenia during working memory tasks relates to maintenance-related processes, manipulation-related (ie, executive) processes, or both. OBJECTIVE: To examine regional functional activations of the brain during maintenance- and manipulation-related working memory processing in patients with schizophrenia and in healthy comparison subjects. DESIGN: Functional images of the brain were acquired in 11 schizophrenic patients and 12 healthy control subjects (matched for age, sex, handedness, and parental education) during 2 spatial working memory paradigms, one contrasting maintenance-only processing with maintenance and manipulation processing and the other contrasting parametrically varying maintenance demands. RESULTS: Patients and controls showed activation of a large, spatially distributed network of cortical and subcortical regions during spatial working memory processing. When task demands required explicit manipulation of information held in memory, controls recruited right dorsolateral prefrontal cortex (Brodmann areas 45 and 46) to a significantly greater extent than patients. A similar effect was observed for the larger memory set sizes of the memory set size task. No other brain regions showed activation differences between groups for either task. These differences persisted when comparing activation maps for memory set sizes in which the 2 groups were equivalent in behavioral accuracy and when comparing subgroups of patients and controls matched for behavioral accuracy on either task. CONCLUSIONS: Physiological disturbances in the dorsolateral prefrontal cortex contribute differentially to patients' difficulties with maintaining spatial information across a brief delay, as well as with manipulating the maintained representation. These differences persisted when comparing conditions in which the 2 groups were equivalent in behavioral accuracy.

Adolescent↗
PubMed2002

Working memory and online syntactic processing in Alzheimer's disease: studies with auditory moving window presentation.

Twenty patients with dementia of the Alzheimer's type (DAT) and 20 controls were tested on six tests of working memory and a test of online auditory sentence comprehension in which listening times for each phrase in the sentence, as well as the time required for an end-of-sentence plausibility judgment, were measured. The sentences differed in syntactic complexity. Patients had lower working memory scores than controls and performed more poorly on the plausibility judgments. However, patients were not more affected than controls by the syntactic complexity of a sentence in these judgments, and both groups showed similar effects of syntactic structure in the listening-time data. The increase in listening times at syntactically capacity-demanding points in complex sentences, compared with comparable points in matched simpler sentences, did not correlate with measures of working memory. The results indicate that early-stage DAT patients are not impaired in their ability to assign syntactic structure and to use it to determine aspects of sentence meaning, despite their reduced working memories. This provides evidence for a specialization within working memory for syntactic processing.

Aged↗
PubMed2000

Verbal working memory in HIV-seropositive drug users.

Recent evidence suggests that HIV-seropositive drug users are impaired on tasks of visuospatial working memory compared with drug users seronegative for HIV. In the current study we evaluated the performance of 30 HIV-seropositive male drug users and 30 risk-matched seronegative controls on two measures of verbal working memory, the Listening Span and the verbal Self Ordered Pointing Task. Impaired working memory performance was significantly more common among HIV-seropositive persons compared to controls, with the highest incidence of deficit among symptomatic participants. These findings indicate that working memory deficits in persons with HIV are not domain-specific and can be demonstrated reliably in drug users.

Adult↗
PubMed2001

The topography of tactile working memory.

To investigate the contribution of topographically organized brain areas to tactile working memory, we asked human subjects to compare the frequency of two vibrations presented to the same fingertip or to different fingertips. The vibrations ranged from 14 to 24 Hz and were separated by a retention interval of variable length. For intervals <1 sec, subjects were accurate when both vibrations were delivered to the same fingertip but were less accurate when the two vibrations were delivered to different fingertips. For 1 or 2 sec intervals, subjects performed equally well when comparing vibrations delivered either to the same finger or to corresponding fingers on opposite hands, but they performed poorly when the vibrations were delivered to distant fingers on either hand. These results suggest that working memory resides within a topographic framework. As a further test, we performed an experiment in which the two comparison vibrations were presented to the same fingertip but an interference vibration was presented during the retention interval. The interpolated vibration disrupted accuracy most when delivered to the same finger as the comparison vibrations and had progressively less effect when delivered to more distant fingers. We conclude that topographically organized regions of somatosensory cortex contribute to tactile working memory, possibly by holding the memory trace across the retention interval. One stimulus can be accurately compared with the memory of a previous stimulus if they engage overlapping representations, but activation of the common cortical territory by an interpolated stimulus can disrupt the memory trace.

Adult↗
PubMed2004

Category-specific modulation of inferior temporal activity during working memory encoding and maintenance.

Findings from neurophysiology have supported the view that visual working memory (WM) relies on modulation of activity in object-selective populations of neurons in inferior temporal cortex. Here, using event-related functional magnetic resonance imaging, we investigated whether similar mechanisms support human visual working memory encoding and maintenance processes. We identified regions in inferior temporal cortex that exhibited category-specific responses during perception of faces (fusiform face area [FFA]) or scenes (parahippocampal place area [PPA]) and investigated whether activity in these regions would be modulated by demands to actively encode and maintain faces and scenes. Results showed that independent of perceptual stimulation, the FFA and PPA exhibited greater encoding- and maintenance-related activity when their favored stimulus was relevant to the recognition task. In contrast, maintenance-related activity in the dorsolateral prefrontal cortex (PFC) was modulated by memory load, regardless of the type of information that was task relevant. These results are consistent with the view that visual working memory encoding and maintenance processes are implemented through modulation of inferior temporal activity by prefrontal cortex.

Adult↗
PubMedDate not supplied

Neocortical ectopias in BXSB mice: effects upon reference and working memory systems.

BXSB mice have an approximately 40-60% incidence of neocortical ectopias in layer I of the prefrontal/motor cortex. Prior studies have found major behavioral differences between those with ectopias and their non-ectopic littermates. Some of these findings indicate that the two groups differ with respect to spatial reference and working memory. The purpose of this study was to measure reference and working memory in the same animals to test the hypothesis that the ectopics would have better reference memory but less effective working memory. The Lashley III maze has cul-de-sacs which must be eliminated, and T-choices where the animal has to decide whether to go left or right. Ectopic and non-ectopic mice were equally able to learn the maze and did not differ on cul-entry or T-choice errors. Then the maze was inverted and the animals were retested. Turning the maze upside down did not change the relative status of the blind alleys. Therefore, the reference memory knowledge from the prior week's training could be used to avoid entering the culs. However, inverting the maze caused a left-right mirror image reversal of the T-choices. Therefore, prior reference memory information would interfere with learning the new path through the maze, whereas working memory would enable the mouse to eliminate T-choice errors. Ectopic mice made less cul-entry errors and more T-choice errors than their non-ectopic littermates, as predicted.

Animals↗
PubMed1997

Is Wisconsin Card Sorting Test performance related to 'working memory' capacity?

The Wisconsin Card Sorting Test (WCST) is a multifactorial and complex test, and it involves so many different kinds of functions that it is difficult to understand why patients fail. Capacity of 'working memory' is possibly involved in the WCST performance and is considered a relevant factor responsible for the schizophrenics' poor performance. The present study was specifically designed to assess the relationship between 'working memory' measurements and WCST performances of schizophrenics. Furthermore, we investigated the relationship between the cognitive dysfunction and the clinical symptomatology. The following tests were administered to 30 schizophrenics and 25 healthy subjects: WCST, Digit Span Test (Backward and Forward), Digit Symbol Substitution Test and Visuo-Spatial 'working memory' Test, a card test appropriately devised. Clinical assessment included the Italian version of the scale of Krawiecka Manchester Scale (K-MS) and the Outcome scale by Strauss and Carpenter (1972). The 30 patients differed significantly in all the neuropsychological variables from the controls. WCST indexes did not correlate significantly with any of the 'working memory' measures (visuo-spatial and verbal) in the samples studied. No relationship was seen between the neuropsychological performances and clinical symptomatology as evaluated by the K-MS scale. WCST indexes and DSST significantly correlated with the outcome measure. The results do not support the hypothesis that executive dysfunction as evaluated by WCST is attributed to 'working memory' impairment, rather they could suggest that these two neuropsychological functions identify different neurocognitive constructs.

Adult↗
PubMed2001

Involvement of pallidothalamic circuitry in working memory.

This study evaluated the capacity of mu-opioid and glutamate receptor agonists to differentially regulate the involvement of the GABAergic projection from the ventral pallidum to the mediodorsal thalamus in working memory and locomotor activity. Microinjection of either the ionotropic glutamate receptor agonist alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) or the mu agonist [D-Ala(2),N-Me-Phe(4),Gly-ol(5)]enkephalin into the ventral pallidum of male Sprague-Dawley rats produced a dose-dependent impairment in working memory, estimated using a forced delayed alternation task in a T-maze. Performance in a spatial discrimination task without delay was also impaired by glutamate, but not by mu receptor, stimulation. Involvement of the GABAergic projection from the ventral pallidum to the mediodorsal thalamus in mu-opioid-induced impairment of working memory was verified by showing that inhibiting GABA(B) receptors in the mediodorsal thalamus blocked the effect of [D-Ala(2),N-Me-Phe(4),Gly-ol(5)]enkephalin in the ventral pallidum. Similarly, either glutamate or mu-opioid receptor stimulation in the ventral pallidum elicited motor activity, and the motor stimulant effect of the mu agonist was blocked, while that of AMPA is not affected by GABA(B) receptor blockade in the mediodorsal thalamus. Distinction between mu and glutamate receptor stimulation was further revealed by the fact that stimulating mu receptors in the ventral pallidum caused a dose-dependent reduction in extracellular GABA levels, while AMPA was without effect on GABA in the ventral pallidum. These data indicate that stimulating mu-opioid receptors reduces GABAergic tone in the ventral pallidum, which increases activity in the GABAergic projection to the mediodorsal thalamus, thereby impairing working memory. Moreover, it is hypothesized that mu receptors in the ventral pallidum gate the recruitment of working memory into ongoing behavioral activity.

Analgesics, Opioid↗
PubMed1999

A developmental functional MRI study of spatial working memory.

Functional magnetic resonance imaging (fMRI) was used to examine patterns of cortical activity in children during performance of a spatial working memory task. Six children (8-10 years) and six adults (19-26 years) searched a linear array of four boxes for the appearance of a dot. In the visual blocks, participants made no response. In the motor blocks, participants were instructed to indicate the location of the dot on each trial using a button-press response. In the working memory blocks, participants were instructed to indicate at which location the dot had appeared 1 or 2 trials previously. Both children and adults showed activity in the left precentral and postcentral gyri, as well as the right cerebellum for the motor condition as compared to the visual condition. Comparison of the memory and motor conditions revealed reliable activity in the right superior frontal gyrus (BA 8), right dorsolateral prefrontal cortex (BA 10/46), right superior parietal cortex, and bilateral inferior parietal cortex for both adults and children. These results suggest that spatial working memory tasks activate very similar cortical regions for school-age children and adults. The findings differ from previous imaging studies of nonspatial working memory tasks in that the prefrontal activations observed in the current work tend to be more dorsal. Results are discussed in light of the significant behavioral performance differences observed between child and adult participants.

Adult↗
PubMed2003

Working memory and schizophrenia: evidence for slowed encoding.

Previous studies have found impairments in working memory in individuals with schizophrenia, but have not identified the underlying information processing deficit. Because schizophrenia is associated with slowed cognitive processing, deficits on working memory tests may be due to decreased speed of encoding rather than an inability to maintain information over time. This hypothesis was examined using a Delayed Match to Sample (DMTS) Test. Task difficulty under 0-delay conditions was equated by individually establishing the stimulus presentation time needed to reach approximately 80% accuracy. Schizophrenia participants required longer presentation durations, but there were no group differences under delay conditions when performance was equated in the 0-delay condition. These results suggest that poor working memory performance in schizophrenia results from slowed encoding processes.

Adolescent↗
PubMed2000

Reflections on working memory: are the two models complementary?

By means of the theoretical modeling of data from Kemps, De Rammelaere, and Desmet (2000, this issue), the working memory theory of Baddeley and the theory of constructive operators of Pascual-Leone are contrasted and compared. It is concluded that although the theory of constructive operators is complementary with working memory theory (for it explains developmental and individual differences that working memory theory cannot explain), the converse is not true; the theory of constructive operators explains all the data without need of working memory theory.

Child↗
PubMed1992

The Roman strains of rats as a psychogenetic tool for pharmacological investigation of working memory: example with RU 41656.

This study examined the effects of RU 41656, a dopaminergic D2 agonist, on the differential working memory performances and on the differential activities of the neurochemical systems of the Roman high (RHA) and Roman low (RLA) avoidance strains of rats. Compared with RLA, RHA performed worse in three tests of working memory (spontaneous alternation, radial maze and object recognition) and had higher levels of exploratory locomotor activity. Hippocampal and frontal cortex choline acetyltransferase (ChAT) activities were lower in RHA. Frontal cortex DA and DOPAC levels, hippocampal and striatal 5-HT and NA levels were higher in RHA. RU 41656 induced a significant improvement in working memory performance of RHA, whereas in RLA it had no effect. It decreased exploratory locomotor activity in both strains. ChAT activity in hippocampus was not affected by RU 41656 in either strain, whereas in frontal cortex it was increased in RHA but not in RLA. Hippocampal NA levels were decreased by RU 41656 in RHA but not in RLA. These results confirm previous data concerning the promnesic effect of RU 41656 and extend the finding that the Roman strains are a psychogenetic model for the behavioural, neurochemical and psychopharmacological study of the working memory in rats.

Animals↗
PubMed1999

Individual differences in working memory and the peak alpha frequency shift on magnetoencephalography.

The effect of the working memory demands on the peak alpha frequency of the power spectrum of magnetoencephalography (MEG) was investigated. There were one control condition and four listening span test (LST) conditions demanding the use of working memory. The results showed that the peak alpha frequency of the averaged MEG power shifted to the higher frequency region in the LST condition dominantly in the fronto-temporal region. Individual differences in working memory capacities were observed in the shift of peak alpha frequency of MEG.

Adult↗