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PubMed2005

Prefrontal and parietal contributions to spatial working memory.

Functional neuroimaging studies consistently implicate a widespread network of human cortical brain areas that together support spatial working memory. This review summarizes our recent functional magnetic resonance imaging studies of humans performing delayed-saccades. These studies have isolated persistent activity in dorsal prefrontal regions, like the frontal eye fields, and the posterior parietal cortex during the maintenance of positional information. We aim to gain insight into the type of information coded by this activity. By manipulating the sensory and motor demands of the working memory task, we have been able to modulate the frontal eye fields and posterior parietal cortex delay-period activity. These findings are discussed in the context of other neurophysiological and lesion-based data and some hypotheses regarding the differential contributions of frontal and parietal areas to spatial working memory are offered. Namely, retrospective sensory coding of space may be more prominent in the posterior parietal cortex, while prospective motor coding of space may be more prominent in the frontal eye fields.

Animals↗
PubMed2005

Double dissociation in neural correlates of visual working memory: a PET study.

Using positron emission tomography (PET), we investigated the organisation of spatial versus object-based visual working memory in 11 normal human subjects. The paradigm involved a conditional colour-response association task embedded within two visual working memory tasks. The subject had to remember a position (spatial) or shape (object-based) and then use this to recover the colour of the matching element for the conditional association. Activation of the nucleus accumbens and the anterior cingulate cortex was observed during the conditional associative task, indicating a possible role of these limbic structures in associative memory. When the 2 memory tasks were contrasted, we observed activation of 2 distinct cortical networks: (1) The spatial task activated a dorsal stream network distributed in the right hemisphere in the parieto-occipital cortex and the dorsal prefrontal cortex, and (2) The non spatial task activated a ventral stream network distributed in the left hemisphere in the temporo- occipital cortex, the ventral prefrontal cortex and the striatum. These results support the existence of a domain-specific dissociation with dorsal and ventral cortical systems involved respectively in spatial and non spatial working memory functions.

Algorithms↗
PubMed2005

Working memory and semantic involvement in sentence processing: a case of pure progressive amnesia.

ED, a 83-year-old woman, meets the criteria of pure progressive amnesia, with gradual impairment of episodic and autobiographical memory, sparing of semantic processing and strong working memory (WM) deficit. The dissociation between disturbed WM and spared semantic processing permitted testing the role of WM in processing anaphors like pronouns or repeated names. Results showed a globally normal anaphoric behavior in two experiments requiring anaphoric processing in sentence production and comprehension. We suggest that preserved semantic processing in ED would have compensated for working memory deficit in anaphoric processing.

Aged, 80 and over↗
PubMed1996

The measurement of verbal working memory capacity and its relation to reading comprehension.

Ninety-four subjects were tested on the Daneman and Carpenter (1980) reading span task, four versions of a related sentence span task in which reaction times and accuracy on sentence processing were measured along with sentence-final word recall, two number generation tasks designed to test working memory, digit span, and two shape-generation tasks designed to measure visual-spatial working memory. Forty-four subjects were retested on a subset of these measures at a 3-month interval. All subjects were tested on standard vocabulary and reading tests. Correlational analyses showed better internal consistency and test-retest reliability of the sentence span tasks than of the Daneman-Carpenter reading span task. Factor analysis showed no factor that could be related to a central verbal working memory; rotated factors suggested groupings of tests into factors that correspond to digit-related tasks, spatial tasks, sentence processing in sentence span tasks, and recall in sentence span tasks. Correlational analyses and regression analyses showed that the sentence processing component of the sentence span tasks was the best predictor of performance on the reading test, with a small independent contribution of the recall component. The results suggest that sentence span tasks are unreliable unless measurements are made of both their sentence processing and recall components, and that the predictive value of these tasks for reading comprehension abilities lies in the overlap of operations rather than in limitations in verbal working memory that apply to both.

Adolescent↗
PubMed2000

The development of working memory: exploring the complementarity of two models.

The aim of the paper was to further explore the complementarity of the working memory models postulated by Pascual-Leone and Baddeley. Five-, six-, eight-, and nine-year-old children were assessed on two working memory tasks that have frequently been used within the respective streams of research: the Mr. Peanut task and the Corsi blocks task. Results indicated a developmental increase in spatial short-term memory for both tasks. Concurrent spatial suppression reduced performance on the two tasks in all four age groups. By contrast, articulatory suppression interfered with recall only on the Mr. Peanut task, and in only the older children. The two models were shown to make their own specific contribution to the interpretation of the data, attesting to their complementarity. Pascual-Leone's theory offered a clear explanation of the results concerning the central aspects of working memory, that is, the stepwise age-related increase in performance, whereas Baddeley's model provided a convincing account of the findings regarding the peripheral phonological and visuo-spatial components, that is, the effects of articulatory and spatial suppression.

Attention↗
PubMed1999

Working memory in aging: maintenance and suppression.

The present research is focused on a fine-grained analysis of memory decline with aging, and the role of suppression mechanisms in age-related memory decline. Three groups of participants (continuous age ranges; young-old: 55-65 years, old: 66-75 years, and old-old: more than 75 years) were administered Forward and Backward span test, and a Working Memory task with Categorization (WMC). This new task requires lists of five words to be processed in order to individuate animal nouns, and that the last word of each list be contemporarily maintained. The words incorrectly recalled as target items, but presented during the task (intrusion errors), were computed in order to analyze the efficiency of suppression mechanisms. The findings indicated a continuous decline in working memory measures, and an early decline in short-term memory (passive storage) measures (between 60's and 70's). An age-related increase in intrusion errors was observed; the intrusion index was inversely related to working memory performance but, according to the hypotheses, was not related to short-term memory measures. These results suggest that the stronger working memory effect observed through age might be due to the combined influence of a decline in the capacity of short-term memory, and a loss of efficiency in suppression mechanisms.

Aged↗
PubMed2006

Age-related changes in duration reproduction: involvement of working memory processes.

The aim of the present research was to study age-related changes in duration reproduction by differentiating the working memory processes underlying this time estimation task. We compared performances of young and elderly adults in a duration reproduction task performed in simple and concurrent task conditions. Participants were also administered working memory tests to measure storage and central executive functions. Findings indicated a differential involvement of working memory storage and central executive functions in age-related differences in temporal tasks. The limited storage capacities explained age-related changes in the simple task of duration reproduction, and the dysfunctioning of central executive functions accounted for age-related changes in duration reproduction performed in a concurrent task condition, which involves greater attentional resources.

Adult↗
PubMed2000

Working memory and executive function: evidence from neuroimaging.

Traditional theories of working memory and executive function, when mapped in straightforward ways into the neural domain, yield predictions that are only partly supported by the recent neuroimaging studies. Neuroimaging studies suggest that some constituent functions, such as maintaining information in active form and manipulating it, are not discretely localized in prefrontal regions. Some hypothesized executive processes, such as goal management, have effects in several cortical regions, including posterior regions. Such results suggest a more dynamic and distributed view of the cortical organization of working memory and executive functions.

Brain Mapping↗
PubMed1995

Working memory and preparation elicit different patterns of slow wave event-related brain potentials.

Some event-related brain potential (ERP) studies of working memory have used delayed match-to-sample designs in which a stimulus (S1) is held in memory for comparison with a subsequent stimulus (S2). During the S1-S2 interval, ERP slow negatives varied with both the type and amount of material held in working memory. One interpretation is that these slow waves index working memory operations. An alternative explanation is that they only reflect general preparatory processing for the response to S2. To decide between these explanations, we used two visual processing tasks that required similar preparation for S2. In one task, visual memory rehearsal operations were required. During the S1-S2 interval, there were clear differences between the amplitudes, topographies, and the effect of information load on the slow waves in two tasks, thus ruling out preparation only as an explanation.

Adult↗
PubMed2005

Variations in working memory capacity predict individual differences in general learning abilities among genetically diverse mice.

Up to 50% of an individuals' performance across a wide variety of distinct cognitive tests can be accounted for by a single factor (i.e., "general intelligence"). Despite its ubiquity, the processes or mechanisms regulating this factor are a matter of considerable debate. Although it has been hypothesized that working memory may impact cognitive performance across various domains, tests have been inconclusive due to the difficulty in isolating working memory from its overlapping operations, such as verbal ability. We address this problem using genetically diverse mice, which exhibit a trait analogous to general intelligence. The general cognitive abilities of CD-1 mice were found to covary with individuals' working memory capacity, but not with variations in long-term retention. These results provide evidence that independent of verbal abilities, variations in working memory are associated with general cognitive abilities, and further, suggest a conservation across species of mechanisms and/or processes that regulate cognitive abilities.

Animals↗
PubMed1990

Opiate antagonists enhance the working memory of rats in the radial maze.

Two experiments tested the influence of the opiate antagonists naloxone and naltrexone on the spatial working memory of rats in a 12-arm radial maze. In Experiment 1, ten rats were serially forced to visit six randomly selected arms, then were removed from the maze for delays of either 30, 60, or 240 minutes, and then returned to the maze for a free-choice memory test with all 12 arms available. Five minutes into the delay, rats were injected intraperitoneally (IP) with either physiological saline or naloxone (1 mg/kg). When injected with naloxone the rats revisited forced-choice arms less often than when injected with saline during a subsequent free-choice test. In Experiment 2, twelve rats showed a similar facilitation of working memory when injected with the opiate antagonists naltrexone (0.3 mg/kg) and naloxone (1 mg/kg) in comparison to a saline control condition. These findings demonstrate the beneficial effects that opiate antagonists exert on working memory-based performance in the radial maze. They may also resolve conflicting reports about the influence of opiate antagonists on radial maze performance, by suggesting that the choice of measurement and testing conditions are crucial for detecting these effects in working memory procedures.

Animals↗
PubMed2002

A comparison of the effects of fimbria-fornix, hippocampal, or entorhinal cortex lesions on spatial reference and working memory in rats: short versus long postsurgical recovery period.

Using a radial maze task and different postoperative recovery periods, this experiment assessed and compared the reference and working memory performances of adult Long-Evans male rats subjected to entorhinal cortex, fimbria-fornix, and hippocampus lesions. Sham-operated rats were used as controls. In order to see whether the duration of the postsurgical recovery period would influence acquisition of the complex radial maze task, training began 1 month following surgery (Delay 1) for half the rats in each group, while for the other half training was started 6.5 months following surgery (Delay 2). The results indicated that at both recovery periods the entorhinal cortex lesions failed to affect either working or reference memory in the spatial task. Conversely, both fimbria-fornix and hippocampus lesions impaired both reference and working memory. While the reference memory deficit was generally similar in both fimbria-fornix and hippocampal lesion groups, analysis of the results for working memory indicated that at the longer delay rats with fimbria-fornix lesions were still impaired but in animals that had the hippocampus removed, working memory did not differ from that of controls. These results suggest that there was some recovery in those rats with hippocampal lesions (e.g., on the working memory task) but both hippocampal and fimbria-fornix animals were still impaired compared to controls when training was delayed 6.5 months following the operations.

Animals↗
PubMed2007

Impaired spatial working memory and altered choline acetyltransferase (CHAT) immunoreactivity and nicotinic receptor binding in rats exposed to intermittent hypoxia during sleep.

Exposure to intermittent hypoxia (IH), such as occurs in sleep-disordered breathing (SDB), is associated with cognitive impairment, neurodegeneration, oxidative stress, and inflammatory responses within rodent brain regions such as the basal forebrain. In this region, damage to cholinergic neurons correlates with working memory deficits in a number of neurodegenerative disorders, suggesting that degeneration of cholinergic systems may also contribute to the working memory impairments observed after IH exposures. We therefore examined basal forebrain choline acetyltransferase (CHAT) immunohistochemistry, nicotinic receptor binding in the prefrontal cortex (PFC), and working memory, in male rats tested on a delayed matching to place (DMP) task in the water maze following exposure to either room air (RA) or intermittent hypoxia (IH; alternating 90s epochs of 21% and 10% O(2) during sleep). IH-treated animals displayed impaired working memory with respect to controls, along with significant reductions in CHAT-stained neurons in the medial septal nucleus, in both the vertical and horizontal limbs of the diagonal band, and the substantia inominata after 14 days of IH exposure. In addition, increases in nicotinic binding and receptor affinity in the PFC were observed after 14 days of IH exposure. Thus, a loss of cholinergic neuronal phenotype in the basal forebrain may contribute to the cognitive impairments associated with CIH exposure. However, compensatory mechanisms may also be activated in other brain regions, and may provide potential therapeutic targets for the cognitive impairments associated with SDB.

Animals↗
PubMedDate not supplied

Working memory, language comprehension, and aging: four experiments to understand the deficit.

Four experiments were carried out to investigate working-memory capacity and functioning in young and older subjects, and its relation with reading comprehension. Experiment 1 showed that older subjects had to trade off processing and storage functions, due to an assumed reduced pool of resources relative to young subjects. Working-memory measures were weakly correlated with reading comprehension in each age group. Experiment 2 revealed a specific processing impairment in older subjects, and showed that older subjects tended to sacrifice the maintenance of the concurrent mnemonic load to devote more resources to ongoing processing. In Experiment 3, the age-related differences in the processing/storage trade-off were again observed. Furthermore, differences in the speed/accuracy trade-off were revealed. Experiment 4 showed that whatever the instructions regarding the speed/accuracy trade-off, the older subjects remained slower and slightly more accurate than the young subjects. In conclusion, it appears that the age-related differences in working memory are both structural and functional. Different strategies may be implemented in each age group to deal with reading comprehension.

Adult↗
PubMed1999

Tyrosine improves working memory in a multitasking environment.

Previous studies indicate that tyrosine may prove useful in promoting improved performance in situations in which performance is compromised by stress. To extend the generality of previous tyrosine findings, the present study examined the effects of tyrosine ingestion on performance during both a Multiple Task and a Simple Task battery. The multiple task battery was designed to measure working memory, arithmetic skills, and visual and auditory monitoring simultaneously, whereas the simple task battery measured only working memory and visual monitoring. Ten men and 10 women subjects underwent these batteries 1 h after ingesting 150 mg/kg of l-tyrosine or placebo. Administration of tyrosine significantly enhanced accuracy and decreased frequency of list retrieval on the working memory task during the multiple task battery compared with placebo. However, tyrosine induced no significant changes in performance on the arithmetic, visual, or auditory tasks during the Multiple Task, or modified any performance measures during the Simple Task battery. Blood levels of ACTH and cortisol were not, but heart rate and blood pressure were significantly increased during the performance tasks. The present results indicate that tyrosine may sustain working memory when competing requirements to perform other tasks simultaneously degrade performance, and that supplemental tyrosine may be appropriate for maintaining performance when mild to severe decrements are anticipated.

Adrenocorticotropic Hormone↗
PubMed2005

Bifrontal transcranial direct current stimulation slows reaction time in a working memory task.

BACKGROUND: Weak transcortical direct current stimulation (tDCS) applied to the cortex can shift the membrane potential of superficial neurons thereby modulating cortical excitability and activity. Here we test the possibility of modifying ongoing activity associated with working memory by tDCS. The concept of working memory applies to a system that is capable of transiently storing and manipulating information, as an integral part of the human memory system. We applied anodal and cathodal transcranial direct current (tDCS) stimulation (260 microA) bilaterally at fronto-cortical electrode sites on the scalp over 15 min repeatedly (15 sec-on/15 sec-off) as well as sham-tDCS while subjects performed a modified Sternberg task. RESULTS: Reaction time linearly increased with increasing set size. The slope of this increase was closely comparable for real and sham stimulation indicating that our real stimulation did not effect time required for memory scanning. However, reaction time was slowed during both anodal and cathodal stimulation as compared to placebo (p < 0.05) indicating that real stimulation hampered neuronal processing related to response selection and preparation. CONCLUSION: Intermittent tDCS over lateral prefrontal cortex during a working memory task impairs central nervous processing related to response selection and preparation. We conclude that this decrease in performance by our protocol of intermittent stimulation results from an interference mainly with the temporal dynamics of cortical processing as indexed by event-related sustained and oscillatory EEG activity such as theta.

Adult↗
PubMed1996

Working memory failure by stimulation of hippocampal adenosine A1 receptors in rats.

THE highly selective adenosine A1 receptor agonist N6-cyclohexyladenosine (CHA) significantly increased the number of errors (attempts to pass through two incorrect panels of the three panel-gates at four choice points) in the working memory task with a three-panel runway setup, when injected bilaterally at 0.3 and 1.0 microgram per side into the dorsal hippocampus. Pretreatment with the selective adenosine A1 receptor antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX; 1 mg kg-1, i.p.) prevented the increase in working memory errors induced by intrahippocampal administration of CHA (1.0 microgram per side). CGS-21680, a highly selective agonist for adenosine A2 receptors, had no effect on the number of working memory errors, when administered intrahippocampally at a dose of 1.0 microgram per side. These results suggest that activation of hippocampal adenosine A1 receptors interferes with neural processes involved in working memory function.

Adenosine↗
PubMed2000

Digit Ordering Test: clinical, psychometric, and experimental evaluation of a verbal working memory test.

Cooper, Sagar, Jordan, Harvey, and Sullivan (1991) proposed a Digit Ordering Test (DOT) for the assessment of verbal working memory: A series of seven digits has to be memorized and immediately recalled in ascending order. In several studies Cooper and co-workers showed selectively reduced DOT performance in patients with Parkinson's disease (PD). We present results from three studies on the properties of this test. In study 1 we replicated the original findings and evaluated a new scoring method. Study 2 addressed the psychometric features of the DOT and provides normative data based on a total of 134 test protocols (PD: 18, other neurological patients: 60, healthy controls: 56). In study 3 we used an experimental modification of the test (DOT-EXP) to evaluate the effects of the presentation rate on serial recall and digit ordering performance. The standard presentation rate of seven digits in 5 s was confirmed as most sensitive for detection of verbal working memory deficits. Findings confirmed that the DOT addresses the manipulatory component of verbal working memory and conveniently detects respective deficits in clinical testing.

Adult↗