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PubMed1985

Effects of pesticides and drugs on working memory in rats: continuous delayed response.

Effects of four pesticides (carbaryl, propoxur, chlordimeform, and deltamethrin) and four reference drugs (physostigmine, scopolamine, methscopolamine, and chlordiazepoxide) were measured in two delayed response, working memory procedures: go-no go alternation in which rats initiated their own trials, and spatial reversals. Four of these compounds (carbaryl, propoxur, physostigmine, and scopolamine) were also tested in a go-no go alternation procedure in which animals did not initiate their trials. The pesticides and physostigmine did not selectively affect working memory in any of the procedures: low doses only moderately decreased response accuracy, whereas higher doses suppressed responding indiscriminately. The pesticides and physostigmine had similar effects on go-no go alternation (i.e., working memory) and analogous go-no go discrimination performance. Effects on go-no go alternation performance did not depend on whether the animals initiated their own trials. Scopolamine, in contrast, appeared to disrupt working memory. It profoundly disrupted accuracy at doses that only moderately decreased over-all responding and impaired go-no go alternation accuracy much more than discrimination accuracy.

Animals↗
PubMed2000

What have Klingon letters and faces in common? An fMRI study on content-specific working memory systems.

Neuroimaging studies show that prefrontal, premotor, and parietal cortical regions are part of a working memory network that supports the active retention of information. In two experiments we used fMRI to examine whether prefrontal and posterior cortical areas are organized in a content-specific way for object and spatial working memory. Subjects performed a delayed matching-to-sample task modified to allow the examination of content-specific retention processes, independent of perceptual and decision-related processes. In Experiment 1, either unfamiliar geometrical objects (Klingon letters from an artificial alphabet unknown to the participants) or their spatial locations had to be memorized, whereas in Experiment 2, either unfamiliar faces or biological objects (butterflies) were actively memorized. All tasks activated a similar cortical network including posterior parietal (banks of the intraparietal sulcus), premotor (banks of the inferior precentral sulcus) and prefrontal regions (banks of the inferior frontal sulcus), and the presupplementary motor area (pre-SMA). For geometrical objects and faces for which strategic semantic processing can be assumed, this activation was larger in the left than in the right hemisphere, whereas a bilateral or right dominant distribution was obtained for butterflies and spatial locations. The present results do not support the process-specific or content-specific view of the role of the prefrontal cortex in working memory task. Rather, they suggest that the inferior prefrontal cortex houses nonmemonic strategic processing systems required for response selection and task management that can flexibly be used across a variety of tasks and informational domains.

Adult↗
PubMed2004

Aging and working memory: early deficits in EEG activation of posterior cortical areas.

Using the n-back task, we recently identified, in young subjects, a positive-negative event related potential component (PN(wm)) in a time-range window between 140 and 280 ms after stimulus onset representing an electrophysiological correlate of working memory load. To evaluate age-related electrophysiological changes in working memory processing, we applied the same neuropsychological paradigm and compared densities of the PN(wm) component in 17 young (mean age: 26) and 17 healthy elderly individuals (mean age: 75). Both age groups displayed a PN(wm) component during the two working memory tasks. For the 1-back task, densities were similar in both young and elderly individuals. In contrast, PN(wm) densities increased with higher memory load (2-back>1-back) in the younger but not in the older group. This difference was mainly observed over parietal electrodes suggesting an impaired activation of neural generators within this brain region. The present results are consistent with the hypothesis of decreased brain reserve in the elderly and provide evidence for age-related deficits in the recruitment of posterior cortical neurons with increasing working memory load.

Adult↗
PubMed2000

The prefrontal cortex: response selection or maintenance within working memory?

It is controversial whether the dorsolateral prefrontal cortex is involved in the maintenance of items in working memory or in the selection of responses. We used event-related functional magnetic resonance imaging to study the performance of a spatial working memory task by humans. We distinguished the maintenance of spatial items from the selection of an item from memory to guide a response. Selection, but not maintenance, was associated with activation of prefrontal area 46 of the dorsal lateral prefrontal cortex. In contrast, maintenance was associated with activation of prefrontal area 8 and the intraparietal cortex. The results support a role for the dorsal prefrontal cortex in the selection of representations. This accounts for the fact that this area is activated both when subjects select between items on working memory tasks and when they freely select between movements on tasks of willed action.

Animals↗
PubMedDate not supplied

Sequencing versus nonsequencing working memory in understanding of rapid speech by older listeners.

The goal of this study was to identify specific neurocognitive deficits that are associated with older listeners' difficulty understanding rapid speech. Older listeners performed speech recognition tests comprised of time-compressed sentences with and without context, and on a neurocognitive battery aimed specifically at testing working memory, processing speed, and attention. A principle component analysis identified three main cognitive components as follows: a sequencing working memory (WM-S) component, a nonsequencing working memory (WM-NS) component, and a processing speed (PS) component. Each of the cognitive component scores was divided into high, mid, and low categories. Sentence performance of the cognitive subgroups was compared within each component. The results showed that, with hearing loss and age accounted for, the cognitive score groups differed similarly on the sentence condition scores also at 50 and 60% time compression, particularly on the subgroups of the WM-S component. The results suggest that deficits in a separate working memory function identified as sequencing were associated with differences in ability to understand time-compressed speech in this study.

Age Factors↗
PubMed2003

The role of spatial working memory in inhibition of return: evidence from divided attention tasks.

Inhibition of return (IOR) refers to a bias against returning attention to a location that has been recently attended. In the present experiments, we examined the role of working memory in IOR by introducing secondary tasks (in the temporal interval between the cue and the target) that involved a working memory component. When the secondary task was nonspatial in nature (monitoring odd digits or adding digits), IOR was present, although overall reaction times were greater in the presence of the secondary task. When the task involved a spatial working memory load (remembering the directionality of arrows or the orientation of objects), IOR was eliminated. However, when the participants had incentive to process the directionality of an arrow but did not have to use any memory system, IOR persisted at peripheral locations. Overall, the results suggest that IOR is partially mediated by a spatial working memory system.

Attention↗
PubMed1994

Coactivation of prefrontal cortex and inferior parietal cortex in working memory tasks revealed by 2DG functional mapping in the rhesus monkey.

Functional studies of the dorsolateral prefrontal cortex and the inferior parietal lobe of the rhesus monkey have implicated the former in spatial mnemonic function and the latter in visuospatial processing. We used the 14C-2-deoxyglucose (2DG) method to assess the contribution of these cortical regions to the cognitive performance of monkeys on working memory tasks. In these experiments, one group of monkeys (WORK) was trained to perform tasks (delayed spatial alternation, spatial delayed response, or delayed object alternation) that specifically engaged working memory processing. Local cerebral glucose utilization (LCGU) rates in the WORK group was compared with LCGU rates for a second group of monkeys (CONT) tested on one of two tasks (visual pattern discrimination or sensory-motor) that relied upon associative memory. The results showed that in comparison to the CONT group, working memory performance significantly enhanced LCGU by 19% in the principal sulcus region of prefrontal cortex and by 11-20% in regions of the inferior parietal cortex corresponding to areas 7A, 7B, 7IP, and 7M. By contrast, LCGU in the auditory cortex was similar for both groups. In all areas examined, metabolic activation peaked in lower layer III where the majority of associational and callosal neurons lie. Correlation analyses of LCGU and behavioral task parameters indicated that LCGU in the parietal subdivisions was significantly related either to the accuracy of performance or to the number of trials completed on the 2DG test. In contrast, LCGU in the principal sulcus was positively correlated with task difficulty. These findings suggest that the enhancement of LCGU in the principal sulcus was primarily influenced by the mnemonic components of the tasks whereas LCGU in the inferior parietal cortex was influenced by their sensory-motor demands. These are the first results showing concurrent metabolic activation of the prefrontal and parietal cortex in monkeys performing working memory tasks and they support the suggestion that these cortical regions represent two important nodes in a neural network mediating spatial working memory in the monkey (Goldman-Rakic, 1988). Further, the present report reinforces the power of the 2DG method for functional mapping as these areal and laminar results could not be readily appreciated at this resolution in any other methodological context.

Animals↗
PubMed2000

Effects of amphetamine on visuospatial working memory performance in schizophrenia spectrum personality disorder.

Our objective was to determine if amphetamine improves visuospatial working memory, which is impaired in the schizophrenia spectrum and may be modulated by dopamine in prefrontal cortex. To this end, oral amphetamine (30 mg) was administered to 12 patients with schizophrenia spectrum personality disorders and 13 patients with other, nonschizophrenia-related personality disorders. Visuospatial working memory was assessed using the Dot test; a test in which subjects are asked to memorize and reproduce the position of a dot on a sheet of paper. Patients with schizophrenia spectrum personality disorders performed significantly worse than the comparison group in the placebo condition and showed significantly greater improvement after amphetamine, as compared to a nonschizophrenia-related personality disorder comparison group. Patients with greatest impairment at baseline improved most. Amphetamine tended to improve negative symptoms; whereas, positive symptoms remained unchanged. Amphetamine may improve visuospatial working memory in schizophrenia spectrum patients.

Adult↗
PubMed2004

Differential cerebellar activation on functional magnetic resonance imaging during working memory performance in persons with multiple sclerosis.

OBJECTIVE: To explore the potential role of the cerebellum in working memory dysfunction in multiple sclerosis (MS). DESIGN: Blood oxygen level dependent functional magnetic resonance imaging (fMRI) was used to examine cerebellar activation during a working memory task. SETTING: University-affiliated medical rehabilitation facility. PARTICIPANTS: Eight persons with MS and 5 healthy controls. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Change in hemodynamic response. fMRI data were acquired and subsequently analyzed by using Statistical Parametric Mapping. RESULTS: Both the control and MS groups showed significantly greater activations in the right cerebellar hemisphere as compared with the left side. Persons with MS, however, showed no detectable activations in 4 cerebellar substructures that were significantly active in controls (ie, right vermis, right dentate nucleus, right tonsil, cerebellar peduncle). CONCLUSIONS: The significantly decreased cerebellar activation in the MS group suggests that the cerebellum may play a role in the working memory impairment observed in MS.

Adolescent↗
PubMed2004

Dissociable functional cortical topographies for working memory maintenance of voice identity and location.

In order to ascertain whether the neural system for auditory working memory exhibits a functional dissociation for spatial and nonspatial information, we used functional magnetic resonance imaging and a single set of auditory stimuli to study working memory for the location and identity of human voices. The subjects performed a delayed recognition task for human voices and voice locations and an auditory sensorimotor control task. Several temporal, parietal, and frontal areas were activated by both memory tasks in comparison with the control task. However, during the delay periods, activation was greater for the location than for the voice identity task in dorsal prefrontal (SFS/PreCG) and parietal regions and, conversely, greater for voices than locations in ventral prefrontal cortex and the anterior portion of the insula. This preferential response to the voice identity task in ventral prefrontal cortex continued during the recognition test period, but the double dissociation was observed only during maintenance, not during encoding or recognition. Together, the present findings suggest that, during auditory working memory, maintenance of spatial and nonspatial information modulates activity preferentially in a dorsal and a ventral auditory pathway, respectively. Furthermore, the magnitude of this dissociation seems to be dependent on the cognitive operations required at different times during task performance.

Acoustic Stimulation↗
PubMed2003

Latent change models of adult cognition: are changes in processing speed and working memory associated with changes in episodic memory?

The authors used 6-year longitudinal data from the Victoria Longitudinal Study (VLS) to investigate individual differences in amount of episodic memory change. Latent change models revealed reliable individual differences in cognitive change. Changes in episodic memory were significantly correlated with changes in other cognitive variables, including speed and working memory. A structural equation model for the latent change scores showed that changes in speed and working memory predicted changes in episodic memory, as expected by processing resource theory. However, these effects were best modeled as being mediated by changes in induction and fact retrieval. Dissociations were detected between cross-sectional ability correlations and longitudinal changes. Shuffling the tasks used to define the Working Memory latent variable altered patterns of change correlations.

Aged↗
PubMed1995

Aging, inhibition, working memory, and speed.

An implication of the hypothesis that failures of inhibition contribution to adult age differences in working memory (Hasher & Zacks, 1988) is that statistical control of measures of inhibition should reduce the age-related effects on working memory. This implication was tested in a study in which interference measures from three variants of a Stroop task served as the measures of inhibition. Although the age-related variance in measures of working memory was substantially reduced after control of the interference measures, the degree of attenuation was at least as large when speed measures from other tasks were controlled. Furthermore, additional analysis revealed that speed measures from tasks requiring oral, written, and keypress responses shared large proportions of their age-related variance. It was suggested that age-related influences on specific processes, such as inhibition, cannot be accurately assessed unless the contributions of more general age-related influences are taken into consideration.

Adult↗
PubMed2000

Visuospatial working memory in schizotypal personality disorder patients.

BACKGROUND: Cognitive processing deficits have been identified as an abnormality that schizotypal personality disorder (SPD) individuals share with schizophrenic patients. It has been hypothesized that impaired working memory may be a critical component of several of the more complex cognitive deficits found in schizophrenia spectrum patients. METHOD: 18 DSM-III-R SPD patients, and 17 normal comparison subjects were compared on a pen and paper visuospatial working memory task. Moreover, we identified a second psychiatric comparison group comprised of nine patients with other, non-odd cluster personality disorder diagnoses who met no more than one of the SPD criteria and were also tested on the same task. Each person was given 14 immediate recall trials and 10 trials using a 10 s delay. RESULTS: SPD patients performed significantly worse than normal control subjects on the working memory task. SPD patients also performed significantly worse compared to the non-schizophrenia-related personality disorder psychiatric comparison group. CONCLUSIONS: Like schizophrenic patients, SPD patients demonstrate working memory impairment compared to normal controls. This impairment may be specific to the schizophrenia-related personality disorders.

Adult↗
PubMed1984

Working memory theory of hippocampal function needs qualification.

To compare the predictive value of "cognitive map" and "working memory" theories of hippocampal function, the performance of rats with dorsal hippocampal lesions was compared to that of control rats in a series of experiments. In Experiment I, experimental rats learned a spatial alternation task with normal ease, but in Experiment II, they were significantly impaired on an elevated 8-arm radial maze. In Experiment III, the performance of the same experimental and control rats was compared on two versions of a 16-arm enclosed radial maze. In the first version, carpet inserts served as cues to mark eight unbaited arms and each of the remaining arms contained one food pellet. While both experimental and control rats successfully avoided the set of cued arms, experimental rats reentered uncued baited arms more frequently than did control rats. In the second version no intramaze cues were provided, but the spatial distribution of baited and unbaited arms remained the same as that used in the first version. In this uncued version, experimental rats both entered unbaited arms and reentered baited arms more frequently than did control rats, i.e., they were impaired in both "reference" and "working" memory. These findings are compatible with the hypothesis that hippocampal lesions result in an impaired capacity to form cognitive maps but they are not compatible with the working memory hypothesis. Furthermore, twelve separate evaluators classed experimental rats as using fewer mapping and more orientation strategies than control rats in the 8-arm maze.

Animals↗
PubMed1990

Mediodorsal thalamic lesions impair "reference" and "working" memory in rats.

The present experiment evaluated the ability of rats with lesions in the thalamic mediodorsal nucleus (MD) to perform a task which differentiates between "reference" and "working" memory. In this task, only four of the arms of an 8-arm radial maze were baited, and animals were to restrict their entries to arms which were baited and to avoid never-baited arms. Despite several postoperative acquisition trials, rats with MD lesions did not acquire the task to a degree comparable to control subjects. Subjects with lesions continued to enter never-baited arms (reference memory errors) and to reenter baited arms (working memory errors). Given the lack of specificity in the behavioural impairment, the reference-working memory distinction seems to be an inappropriate one for characterizing the MD lesion deficit in rats. This deficit may involve an inability to use environmental stimuli to distinguish among arms of the maze, or an alteration in motor mechanisms.

Animals↗
PubMed2001

Cerebellar contribution to spatial event processing: involvement in procedural and working memory components.

Spatial function is one of the cognitive functions altered in the presence of cerebellar lesions. We investigated the cerebellar contribution to the acquisition of spatial procedural and working memory components by means of a radial maze. To establish whether a cerebellar lesion would cause a deficit in solving the radial maze, a first experiment was carried out by using a full-baited maze procedure in different experimental groups, with or without cerebellar lesion and with or without pretraining. Non-pretrained hemicerebellectomized (HCbed) animals exhibited impaired performances in all (motor, spatial and procedural) task aspects. Pre-trained HCbed animals performed similarly to control animals in the task aspects linked to the processing of spatial and procedural factors. To distinguish procedural from working memory components, a forced-choice paradigm of the radial maze was used in the second experiment. Non-pretrained HCbed rats continued to make a lot of errors and show severe perseverative tendencies, already observed in the first experiment, supporting a specific cerebellar role in acquiring new behaviours and in modifying them in relation to the context. Interestingly, hindered from putting the acquired explorative patterns into action and compelled to use only working memory abilities, the pretrained HCbed group exhibited a dramatic worsening of performance. In conclusion, the present findings demonstrate that cerebellar damage induces a specific behaviour in radial maze tasks, characterized by an inflexible use of the procedures (if indeed any procedure was acquired before the lesion) and by a severe impairment in working memory processes.

Animals↗
PubMed2002

Arithmetic fact retrieval and working memory in schizophrenia.

Despite its importance in every-day life and vocational rehabilitation, arithmetic ability has rarely been investigated in schizophrenic patients. Those few studies reporting arithmetic deficits in schizophrenia, however, administered complex calculation tasks which drew not only on arithmetic abilities, but also on working memory resources known to be impaired in schizophrenia. In the present study, arithmetic abilities and working memory functions were investigated in schizophrenic patients (n=24) and healthy control subjects (n=24). Arithmetic fact retrieval was assessed in single-digit multiplication and corresponding division problems using a result verification task which minimized working memory demands. Problem size and the disparity of the proposed result were manipulated. The storage component of working memory was tested with a digit span forward task and the executive control component with a digit span backward as well as with verbal fluency tasks. Schizophrenic patients performed worse than controls only in the executive tasks. Digit span forward was preserved. In the arithmetic tasks, groups did not differ from each other, and a similar pattern of task manipulations was obtained. Hence, despite the executive control deficit retrieval of arithmetic facts is preserved in schizophrenia. Moreover, the same underlying cognitive processes as in control subjects are involved.

Adult↗
PubMed1999

Prefrontal cortical involvement in visual working memory.

Studies of human amnesia provide evidence for a short-term memory store with information transfer to long term memory occurring within 60 s of sensory encoding. Human and nonhuman primate research has shown that maintenance of this short-term or working memory store is dependent upon frontal cortical activation, although the critical temporal parameters of frontal involvement throughout this 60-s window are undetermined. We examined prefrontal contributions to rapid (under 2 s) and sustained (over 4 s) visual working memory by recording behavioral performance and event-related potentials (ERPs) in patients with lesions in dorsolateral frontal cortex and age-matched control subjects. Prefrontal lesioned patients generated a reduced sustained frontal positivity at all delays. At short delays, patients generated reduced performance to stimuli presented in the contralesional field. Patients generated a negative potential (N400), greatest to contralesionally presented stimuli, that was observed in the control subjects only at long delays. The results indicate that prefrontal lesions impair the frontal component of an anterior-posterior working memory network activated during rapid and sustained visual memory processing. Frontal patients may require activation of limbic cortex, indexed by N400, for maintenance of both rapid and sustained working memory.

Aging↗