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PubMed2006

The role of inferior parietal and inferior frontal cortex in working memory.

Verbal working memory involves two major components: a phonological store that holds auditory-verbal information very briefly and an articulatory rehearsal process that allows that information to be refreshed and thus held longer in short-term memory (A. Baddeley, 1996, 2000; A. Baddeley & G. Hitch, 1974). In the current study, the authors tested two groups of patients who were chosen on the basis of their relatively focal lesions in the inferior parietal (IP) cortex or inferior frontal (IF) cortex. Patients were tested on a series of tasks that have been previously shown to tap phonological storage (span, auditory rhyming, and repetition) and articulatory rehearsal (visual rhyming and a 2-back task). As predicted, IP patients were disproportionately impaired on the span, rhyming, and repetition tasks and thus demonstrated a phonological storage deficit. IF patients, however, did not show impairment on these storage tasks but did exhibit impairment on the visual rhyming task, which requires articulatory rehearsal. These findings lend further support to the working memory model and provide evidence of the roles of IP and IF cortex in separable working memory processes.

Adult↗

PubMed2005

Linkage analyses of event-related potential slow wave phenotypes recorded in a working memory task.

Working memory is an essential component of wide-ranging cognitive functions. It is a complex genetic trait probably influenced by numerous genes that individually have only a small influence. These genes may have an amplified influence on phenotypes closer to the gene action. In this study, event-related potential (ERP) phenotypes recorded during a working-memory task were collected from 656 adolescents from 299 families for whom genotypes were available. Univariate linkage analyses using the MERLIN variance-components method were conducted on slow wave phenotypes recorded at multiple sites while participants were required to remember the location of a target. Suggestive linkage (LOD > 2.2) was found on chromosomes 4, 5, 6, 10, 17, and 20. After correcting for multiple testing, suggestive linkage remained on chromosome 10. Empirical thresholds were computed for the most promising phenotypes. Those on chromosome 10 remained suggestive. A number of genes reported to regulate neural differentiation and function (i.e. NRP1, ANK3, and CHAT) were found under these linkage peaks and may influence the levels of neural activity occurring in individuals participating in a spatial working-memory task.

Adolescent↗

PubMed2002

Information processes in the primate prefrontal cortex in relation to working memory processes.

Working memory is a mechanism for short-term active storage of information as well as for processing stored information. Although evidence for neuronal mechanisms of temporary storage of information has accumulated for the prefrontal cortex, little is known about neuronal mechanisms for processing information. To understand how information is processed by prefrontal neurons, we first need to know what information is represented by single-neuron activity, and then examine how information represented by single-neuron activity or a population of activities changes along the temporal sequence of the trial. By examining task-related single-neuron activities while monkeys performed various working memory tasks, delay-period activity observed in the prefrontal cortex is considered to be a neuronal correlate of the mechanism for temporary active storage of information. Delay-period activity represents a variety of information including the spatial position and the physical feature of the stimulus, the forthcoming behavioral response, the quality of reward that the subject would receive, the difference of the task, or the rule of the task. Although delay-period activity could represent this variety of information, the information represented by delay-period activity is only the information relevant for task performance. In addition, using complex conditional tasks, delay-period activity has been shown to represent several kinds of information simultaneously. Based on these results, we examined how information represented by a population of prefrontal activities changes along the temporal sequence of the trial. Using two kinds of oculomotor delayed-response tasks, we first identified what information each task-related activity represents. Then, using population vector analysis, we could not only visualize information represented by a population of prefrontal activities, but also demonstrate the temporal change of information represented by a population of prefrontal activities. These attempts are important to understand information processes for working memory.

Animals↗

PubMed1996

The hippocampus: a "working memory" structure? The effect of hippocampal sclerosis on working memory.

Patients with medically intractable epilepsy and either hippocampal sclerosis or frontal lobe lesions were compared with healthy controls, to investigate a possible neuroanatomical correlate of a component of working memory: the central executive. Patients were tested on a short-term memory task which comprised visuo-spatial and verbal components, in single and concurrent trials. Differences were found between the patient groups for dual-task capacity, despite being equated on single-task trials. Patients with frontal lobe damage were the most affected by the demands of attention division. The results of this study do not support the thesis of a hippocampal role in the working memory component examined, but point to a frontal lobe focus for this janusian cognitive function. An unexpected finding of an increment in performance over the trials of visuo-spatial assessment, in patients with hippocampal sclerosis, is presented.

Analysis of Variance↗

PubMed2003

N-methyl-D-aspartate receptor in working memory impairments in schizophrenia: event-related potential study of late stage of working memory process.

Working memory (WM) deficit in schizophrenic patients has been well established. Still, underlying biological substrate of the impairment is not clear. Among neurotransmitter hypotheses of schizophrenia, N-methyl-D-aspartate (NMDA) receptor model is mostly supported, considering that NMDA receptor antagonist can elicit both psychosis and cognitive impairment observed in schizophrenic patients. In current study, to test the neuropsychological and the electrophysiological effects of NMDA receptor in WM, event-related potentials (ERPs) of Sternberg's short-term memory scanning task (SMST) were analyzed in 10 healthy subjects under intravenous administration of a subanesthetic dose of ketamine (0.65 mg/kg/h) or placebo (normal saline). Late positive component (LPC) of ERP was hypothesized to reflect later stage of WM. Brief Psychiatric Rating Scale score was significantly increased (t=-5.75, df=9, P<.001) and correct response rate was significantly decreased (t=2.21, df=9, P=.054) after ketamine administration. Neither reaction time nor LPC latency, which reflect memory scanning time, was changed. Amplitude of LPC was significantly reduced after ketamine administration (z=-2.31, number of observations=120, P=.021). In conclusion, NMDA receptor antagonist administration elicited WM deficit both in behavioral and electrophysiological level. Electrophysiological component reflecting later stage of WM was impaired by NMDA antagonist.

Adult↗

PubMed2006

On the waxing and waning of working memory: action orientation moderates the impact of demanding relationship primes on working memory capacity.

The present research examined how action- versus state-oriented individuals (Kuhl & Beckmann, 1994) utilize their working memory capacity under varying situational demands. Participants visualized either a demanding or an accepting person, after which their working memory capacity was assessed. Among action-oriented participants, visualizing a demanding person led to greater operation spans (Study 1) and superior memory for intention-related information (Study 2) than visualizing an accepting person. State-oriented participants displayed the opposite pattern, such that visualizing an accepting person led to greater operation spans (Study 1) and superior memory for intentions (Study 2) than visualizing a demanding person. These findings indicate that action versus state orientation moderates the impact of situational demands on working memory capacity.

Adult↗

PubMed2002

Similarities and differences in the neural correlates of episodic memory retrieval and working memory.

Functional neuroimaging studies have shown that different cognitive functions activate overlapping brain regions. An activation overlap may occur because a region is involved in operations tapped by different cognitive functions or because the activated area comprises subregions differentially involved in each of the functions. To investigate these issues, we directly compared brain activity during episodic retrieval (ER) and working memory (WM) using event-related functional MRI (fMRI). ER was investigated with a word recognition test, and WM was investigated with a word delayed-response test. Two-phase trials distinguished between retrieval mode and cue-specific aspects of ER, as well as between encoding/maintenance and retrieval aspects of WM. The results revealed a common fronto-parieto-cerebellar network for ER and WM, as well as subregions differentially involved in each function. Specifically, there were two main findings. First, the results differentiated common and specific subregions within the prefrontal cortex: (i) left dorsolateral areas were recruited by both functions, possibly reflecting monitoring operations; (ii) bilateral anterior and ventrolateral areas were more activated during ER than during WM, possibly reflecting retrieval mode and cue-specific ER operations, respectively; and (iii) left posterior/ventral (Broca's area) and bilateral posterior/dorsal areas were more activated during WM than during ER, possibly reflecting phonological and generic WM operations, respectively. Second, hippocampal and parahippocampal regions were activated not only for ER but also for WM. This result suggests that indexing operations mediated by the medial temporal lobes apply to both long-term and short-term memory traces. Overall, our results show that direct cross-function comparisons are critical to understand the role of different brain regions in various cognitive functions.

Adult↗

PubMed2002

Manipulation of working memory information is impaired in Parkinson's disease and related to working memory capacity.

It has been suggested that in patients with Parkinson's disease (PD), difficulties in the manipulation of information, which result in problems in executive tasks, are related to a reduction of working memory capacity (J. D. E. Gabrieli, J. Singh, G. T. Stebbins, & C. G. Goetz, 1996). The present study selectively varied the manipulation demand irrespective of the maintenance requirement. In a group of 14 PD patients, performance declined overproportionally with the increasing task demand and was significantly correlated with a measure of working memory capacity. These results suggest that the complexity of working memory processing may decisively contribute to the exhaustion of resources in PD patients. Increasing complexity may either affect their manipulation ability directly or impede the management of inhibitory control requirements inherent to the task.

Adult↗

PubMed2004

Can delay-period activity explain working memory?

Working-memory tasks often lead to elevated delay-period discharge rates in cortical neurons. When this altered neuronal discharge rate, called delay activity, shows stimulus specificity, it is a good candidate for a neuronal mechanism of working memory. If the delay activity is indeed the carrier of memory, then experimental manipulation during the delay period that disrupts delay activity should also disrupt behavioral performance. We tested this hypothesis in two macaque monkeys with a delayed matching-to-sample task (delay time: 8 or 10 s) in which only two visual images were used. In each trial, one of the images was randomly chosen as the sample. In control trials (without disruptive stimulation), the monkeys performed at the level of 74.3% correct recognition. Three electrical stimulation levels (mild: a 0.25-s train of electrical pulses; medium: 1-s train; strong: 4 s), delivered to the hippocampal formation or to the orbito-frontal and inferotemporal cortices during delay period, decreased the performance to 71.4, 66.8, and 58.0% respectively (all are significantly less than control performance, P < 0.05 for mild stimulation and P < 0.0001 for other stimulation levels). Three hundred and thirty-four cells were recorded from inferotemporal (211 cells) and prefrontal (123 cells) cortices. Significant (P < 0.05) stimulus-specific delay activity was found in about one-third of recorded cells. For these cells in control trials, the mean difference in delay-period spike rates between preferred and nonpreferred images was 26%. The electrical stimulation reduced this difference to 20% (not a statistically significant reduction) in trials with mild stimulation, to 14% (P < 0.05) with medium stimulation, and just to 4% (P < 0.0005) with strong stimulation. These results, that increasing electrical stimulation reduced neuronal selectivity and at the same time reduced behavioral performance, directly support the hypothesis that delay activity is the carrier of memory through the delay period.

Action Potentials↗

PubMed2000

Neurocomputational models of working memory.

During working memory tasks, the firing rates of single neurons recorded in behaving monkeys remain elevated without external cues. Modeling studies have explored different mechanisms that could underlie this selective persistent activity, including recurrent excitation within cell assemblies, synfire chains and single-cell bistability. The models show how sustained activity can be stable in the presence of noise and distractors, how different synaptic and voltage-gated conductances contribute to persistent activity, how neuromodulation could influence its robustness, how completely novel items could be maintained, and how continuous attractor states might be achieved. More work is needed to address the full repertoire of neural dynamics observed during working memory tasks.

Action Potentials↗

PubMed2002

The phonological-similarity effect differentiates between two working memory tasks.

Working memory is a set of interactive cognitive processes that maintain information on-line and available for analysis. Part of the system is specialized for maintaining verbal information, a core component of which is thought to be a phonological store. On the basis of the study of patients with acquired brain lesions, this store has been localized to the supramarginal and angular gyri of the speech-dominant hemisphere, and some functional neuroimaging studies support this localization. However, other imaging studies localize the phonological store in a more dorsal region of the parietal lobe. To reconcile these findings, we examined the phonological-similarity effect in two different tasks. A phonological-similarity effect was observed only in the task that involved sequential presentation and explicit verbal rehearsal. We conclude that at least one possible source of the differences in brain activation between different working memory tasks may be differences in phonological processing.

Adult↗

PubMed2002

Frontal theta activity in humans increases with memory load in a working memory task.

Recent theoretical work has suggested that brain oscillations in the theta band are involved in active maintenance and recall of working memory representations. To test this theoretical framework we recorded neuromagnetic responses from 10 subjects performing the Sternberg task. Subjects were required to retain a list of 1, 3, 5 or 7 visually presented digits during a 3-s retention period. During the retention period we observed ongoing frontal theta activity in the 7-8.5-Hz band recorded by sensors over frontal brain areas. The activity in the theta band increased parametrically with the number of items retained in working memory. A time-frequency analysis revealed that the task-dependent theta was present during the retention period and during memory scanning. Following the memory task the theta activity was reduced. These results suggest that theta oscillations generated in frontal brain regions play an active role in memory maintenance.

Adult↗

PubMed2006

How rats perform spatial working memory tasks: limitations in the use of egocentric and idiothetic working memory.

Rats of the Dark Agouti strain were trained on delayed alternation under conditions that should encourage egocentric working memory. In two experiments a T-maze was set within a cross-maze so that different arms could be used for the sample and test runs. The maze had high opaque side-walls, and testing was conducted in low light levels so that distal visual cues might be eliminated. By rotating the maze 90 degrees between the sample and choice run and by using two identical mazes set side by side it was possible to nullify other spatial strategies. Experiments 1 and 2 showed that rats preferentially used place information, intramaze cues, and direction cues, even though only egocentric or idiothetic (nonmatch-to-turn) working memory could successfully solve every trial. Rats were able to maintain an accurate sense of location within the maze even though distal cues were not visible and the animal was moved between the sample and choice runs. Experiment 2 confirmed that another rat strain (Long-Evans) shows the same learning profiles. Both experiments indicate that rats are very poor at using either egocentric or idiothetic information to alternate, and that retention delays as short as 10 s can eliminate the use of these forms of memory.

Animals↗

PubMed2005

Muscarinic and nicotinic receptor modulation of object and spatial n-back working memory in humans.

Working memory impairments in the n-back task in schizophrenia have been linked to sustained deficiency in mesocortical dopamine function. More recently, abnormalities in the cholinergic system have also been documented in schizophrenia, with cortical reductions in both nicotinic and muscarinic receptors. While the cholinergic hypothesis of memory is well established, the role of cholinergic receptors in modulating n-back working memory is not known. We investigated the effects of selective and simultaneous muscarinic and nicotinic antagonism on spatial and object n-back working memory performance. The study was a double-blind, placebo-controlled repeated-measures design in which 12 healthy subjects were tested under four acute treatment conditions; placebo (P), mecamylamine (M), scopolamine (S) and mecamylamine+scopolamine (MS). Muscarinic antagonism with scopolamine significantly impaired both object and spatial n-back working memory, whereas nicotinic antagonism with mecamylamine had little effect. Simultaneous antagonism of both muscarinic and nicotinic receptors produced greater impairments in both object and spatial n-back working memory performance than muscarinic or nicotinic antagonism alone. These results suggest that: (1) both muscarinic and nicotinic receptors may functionally interact to synergistically modulate n-back working memory, and (2) that n-back working memory impairments in schizophrenia may in part be due to reductions in both muscarinic and nicotinic receptors.

Adult↗

PubMedDate not supplied

Field dependence-independence from a working memory perspective: a dual-task investigation of the Hidden Figures test.

Field dependence-independence (FDI) is a construct intensively investigated within cognitive style research, but its cognitive underpinnings are not clearly specified. We propose that performance on FDI tasks primarily reflects the operations of the visuospatial and executive components of working memory. We tested this hypothesis in a dual-task experiment with a commonly used measure of FDI, the Hidden Figures Test. The results showed that performance on this test was impaired by concurrent performance of secondary tasks that primarily tap the visuospatial component (spatial tapping) and the executive component (2-back and random number generation), but was almost unaffected by other secondary tasks (simple tapping and articulatory suppression). Moreover, an analysis of secondary task performance ruled out the possibility of strategic trade-offs and revealed an intriguing dissociation for two different sets of "randomness" indices for the random number generation task. These results support the hypothesised mapping between FDI and working memory components and suggest that the dual-task paradigm can provide a useful way to bring underspecified constructs like FDI into closer alignment with theoretical ideas developed within cognitive psychology.

Field Dependence-Independence↗

PubMed2006

The relationship between working memory and episodic memory disorders in transient global amnesia.

In a previous study, we investigated the relationship between the disorders of both episodic memory and working memory in the acute phase of transient global amnesia (TGA). Since executive functions were spared, another dysfunction may be responsible for the binding and maintenance of multimodal informations and contribute to the encoding disorders observed in some patients [Quinette, P., Guillery, B., Desgranges, B., de la Sayette, V., Viader, F., & Eustache, F. (2003). Working memory and executive functions in transient global amnesia. Brain, 126, 1917-1934.]. The aim of this present study was to assess the functions of binding and maintenance of multimodal information during TGA and explore their involvement in episodic memory disorders. We therefore conducted a more thorough investigation of working memory in 16 new patients during the acute phase of TGA using two tasks designed to assess the binding process and both dimensions of the maintenance, namely the active storage and the memory load ability. We also investigated the nature of the episodic memory impairment in distinguishing between the performance of patients with preferential encoding deficits and those of patients with preferential storage disorders on the episodic memory task. This distinction was closely related to the severity of amnesia, i.e. an encoding disorder was observed rather in the early phase of TGA. The results showed that while the functions of binding and maintenance of multimodal information were intact in patients with storage disorders, they were impaired in the case of encoding deficits. These results are interpreted in the recent framework of episodic buffer proposed by Baddeley [Baddeley, A. D. (2000). The episodic buffer: A new component of working memory? Trends in Cognitive Sciences, 4, 417-423] that represents an interface between working memory and episodic memory.

Aged↗

PubMed2004

Nitrous oxide impairs selective stages of working memory in rats.

Working memory impairment under narcosis has never been investigated. Furthermore, mechanisms by which narcosis disturbs working memory processes remain relatively unknown. The present work was aimed at answering to these two questions using a well-known normobaric narcotic gas, nitrous oxide (N2O), and a classical working memory task (a two-trial recognition memory task). Ten Long-Evans rats were tested in this behavioral task under nitrous oxide exposure. The results showed (i) a dose-related impairment of working memory, (ii) a selective effect of N2O on two out of three mnemonic processes: acquisition, and retention, and (iii) a compensatory effect of increasing the acquisition phase duration on these impairments. These results, as previously suggested for long-term memory, agree with the fact that nitrous oxide disrupts in a dose-related manner working memory by notably slowing down acquisition processes.

Analgesics, Non-Narcotic↗

PubMed1995

Temporal interval production and processing in working memory.

Short-term memory or working memory has been proposed as a cognitive structure contributing to time estimation. Thus, in a previous experiment, retrieving a stored item during a temporal-interval production lengthened the interval in proportion to the number of items in the memory set. In the present study, this issue was analyzed further by testing whether the proportional lengthening is induced by the load itself (i.e., the number of items) or by comparing the probe with memorized items. In a first experiment, a memory set was maintained during a temporal production, and the comparison of the probe with memorized items was postponed until the end of time production. Varying the number of items in the memory set had no effect on temporal intervals produced during its retention, suggesting that mental comparison was the source of the lengthening of time intervals. In succeeding experiments, tasks requiring processing in working memory but involving no memory load were combined with temporal production. In Experiment 2, increasing the number of syllables in a rhyme-judgment task proportionally lengthened temporal intervals that were produced simultaneously. In Experiment 3, increasing the amount of mental rotation in a task involving visuospatial processing also lengthened simultaneous temporal production. This interference between processing in working memory and time estimation suggests that working memory, defined as a work space for active processing of current information, contributes to time estimation.

Adult↗