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At least 1,333 records · Page 74Linked to original sources
PubMed1989

The effect of embryonal amygdala grafts on the impairment of spatial working memory elicited in rats by kainate-induced amygdaloid damage.

The effect of epileptogenic lesion of amygdala on spatial working memory was examined in rats after unilateral (U, n = 9) or bilateral (B, n = 8) injection of 1 or 0.5 mu of 0.2% kainate into the amygdaloid complex. Another group of unilaterally lesioned rats (T, n = 9) received 8 days after kainate injection grafts of embryonal (E 20) amygdala into the damaged region. Twelve days after lesion the three experimental groups and an unoperated control group (C, n = 11) were trained during three weeks in the aversively motivated 8-arm radial water maze (RWM). Training decreased incidence of errors/8 choices from the initial 2.3 to 1.2 in the lesioned rats and to 0.4 in the controls. Transplantation did not enhance RWM acquisition but restored the symmetrical pattern of choices and normalized the emotionality of lesioned animals. Retraining the RWM task 3 months later revealed significant savings in the control group but not in the transplanted group. Histology showed in addition to large lesion at the injection site also distant lesions in the ipsilateral hippocampus, thalamus and neocortex and in the unilaterally injected rats also in the contralateral amygdala. Healthy, well integrated transplants found in 6 out of 9 transplanted rats reduced the incidence of remote lesions (particularly in the contralateral hemisphere). Performance of individual animals reflected the state of the transplant. It is concluded that the impairment of spatial working memory is due not only to destruction of amygdala but also to diffuse damage of the limbic system. The slowly developing seizure-induced distant lesions can be partly prevented by embryonal grafts.

Amygdala↗
PubMed1993

The psychopathology, neuropsychology, and neurobiology of associative and working memory in schizophrenia.

A large number of psycholinguistic findings on how human beings store lexical information suggest the existence of associative memory, which may be characterized by a large capacity and a long duration. Its anatomical basis supposedly is, at least in part, the frontal lobes, and some of its functional characteristics have been tentatively linked to dopamine release. Working memory has a limited capacity, lasts only for seconds and is relevant for goal-directed behavior. Its anatomical basis in the frontal cortex is established and strong evidence suggests the involvement of dopaminergic pathways. Experimental evidence using several lexical decision tasks and a delayed response task is provided to demonstrate that some characteristic features of schizophrenic thinking--in particular the rapid shift of associations, the indirect relationship of associations, the overly abstract or overly concrete use of concepts, the lack of context-sensitivity and of general integrative function and intellectual capacity--can be explained in terms of an activation or disinhibition of associative memory, and of a dysfunctional working memory. The findings serve as an example of schizophrenia research in a cognitive neuroscience framework.

Adult↗
PubMed2004

Dopaminergic modulation of visual attention and working memory in the rodent prefrontal cortex.

Converging evidence suggests that dopaminergic projections to the prefrontal cortex (PFC) modulate both attention and working memory processes that may be related to either insufficient or excessive dopamine activity specific to a D1 receptor mechanism. We examined the effects of bilateral intraprefrontal cortical infusions of the D1 agonist (SKF 81297) on a novel task specifically designed to assess the animals' ability to attend to a visual target (0.7 or 0.5 s) and then remember the location of that target over a variable delay (0-16 s) within the same test session. Bilateral prefrontal infusions of the low dose of SKF 81297 (0.01 microg) had no effect on visual attention or memory throughout the entire testing schedule. The medium (0.06 microg) dose preferentially increased attention to the stimulus target but only improved memory for that stimulus at a duration of 0.7 s, although in a delay-independent manner. The high dose (0.3 microg) of the D1 agonist also increased attentional accuracy. However, it was only under the more attention challenging condition (0.5 s) that this high dose also produced a baseline delay-dependent modulation of memory for the stimulus target. Specifically, good memory at the short delay was impaired and poor memory at the long delay was improved. These data provide the first demonstration that dopamine D1 receptor stimulation sufficient to improve attentional accuracy, can also disrupt, and facilitate short-term working memory performance in a delay-dependent manner.

Animals↗
PubMed2004

Functional imaging of working memory after 24 hr of total sleep deprivation.

The neurobehavioral effects of 24 hr of total sleep deprivation (SD) on working memory in young healthy adults was studied using functional magnetic resonance imaging. Two tasks, one testing maintenance and the other manipulation and maintenance, were used. After SD, response times for both tasks were significantly slower. Performance was better preserved in the more complex task. Both tasks activated a bilateral, left hemisphere-dominant frontal-parietal network of brain regions reflecting the engagement of verbal working memory. In both states, manipulation elicited more extensive and bilateral (L>R) frontal, parietal, and thalamic activation. After SD, there was reduced blood oxygenation level-dependent signal response in the medial parietal region with both tasks. Reduced deactivation of the anterior medial frontal and posterior cingulate regions was observed with both tasks. Finally, there was disproportionately greater activation of the left dorsolateral prefrontal cortex and bilateral thalamus when manipulation was required. This pattern of changes in activation and deactivation bears similarity to that observed when healthy elderly adults perform similar tasks. Our data suggest that reduced activation and reduced deactivation could underlie cognitive impairment after SD and that increased prefrontal and thalamic activation may represent compensatory adaptations. The additional left frontal activation elicited after SD is postulated to be task dependent and contingent on task complexity. Our findings provide neural correlates to explain why task performance in relatively more complex tasks is better preserved relative to simpler ones after SD.

Adult↗
PubMed2004

Complexity factors in visuo-spatial working memory.

Three experiments are presented that use a technique of selective interference--irrelevant pictures--to develop our understanding of visuo-spatial working memory. Visual noise fields are used as the irrelevant pictures. Using two related measures of simple visual complexity, the experiments demonstrate that the greater the complexity the greater the degree of interference, even within a paradigm where subjects are instructed to look at but otherwise ignore the irrelevant pictures. Both the number of dots and the density of the dots comprising the visual noise fields affect the degree of interference in a concurrent memory task. In addition, increasing the size of the field increases the amount of interference. It is argued that the results give insight into the properties of visual working memory and contribute to its theoretical development. For example, it is argued that the store is directly accessible by externally presented interference and that particular aspects of the noise displays cause interference with visual memory.

Humans↗
PubMed2000

The role of spatial selective attention in working memory for locations: evidence from event-related potentials.

We investigated the hypothesis that the covert focusing of spatial attention mediates the on-line maintenance of location information in spatial working memory. During the delay period of a spatial working-memory task, behaviorally irrelevant probe stimuli were flashed at both memorized and nonmemorized locations. Multichannel recordings of event-related potentials (ERPs) were used to assess visual processing of the probes at the different locations. Consistent with the hypothesis of attention-based rehearsal, early ERP components were enlarged in response to probes that appeared at memorized locations. These visual modulations were similar in latency and topography to those observed after explicit manipulations of spatial selective attention in a parallel experimental condition that employed an identical stimulus display.

Adult↗
PubMed1998

Impairment of working memory in the T-maze after transient global cerebral ischemia in the Mongolian gerbil.

Using a T-maze, the influence of transient global cerebral ischemia on working memory in gerbils was investigated. Furthermore, it was examined whether a correlation exists between impairment in choice accuracy in the T-maze and neuron loss in the hippocampus. In two experiments, male Mongolian gerbils were tested in a previously learned delayed alternation T-maze task 1 week after a 4 min occlusion of the common carotid arteries. In both experiments memory was significantly impaired and in the second experiment, where the design allowed a separation between working and reference memory deficits, a selective impairment in working memory was seen. The results suggest that ischemia-induced disruption of delayed alternation in the T-maze in gerbils is a model which is relevant to the clinical manifestations of vascular dementia.

Animals↗
PubMed1998

5-HT1A receptor agonist (8-OH-DPAT) and 5-HT2 receptor agonist (DOI) disrupt the non-cognitive performance of rats in a working memory task.

The present study investigated the role of 5 -HT1A and 5 -HT2 receptors in the execution of a working memory task (delayed non-matching to position, DNMTP) by assessing the influence of 8-OH-DPAT (5-HT1A receptor agonist) and DOI (5-HT2 receptor agonist) on the performance of rats lesioned with 5,7-dihydroxytryptamine (5,7-DHT) and their controls. Post-mortem neurochemical analysis revealed that serotonin and 5-hydroxyindoleacetic acid levels were reduced in examined brain areas (especially in the hippocampus where there was a 90 percent reduction). Noradrenaline concentrations were also decreased (mostly on the same side of the injection) by about 20 percent. 5,7-DHT lesioned rats did not significantly differ from their controls in performance in the DNMTP task. At the 30 microg/kg dose, 8-OH-DPAT did not affect the DNMTP-performance of rats, but at the higher dose (100 microg/kg) it reduced the probability of responding to the sample lever. DOI (100 and 300 microg/kg) also interfered with the non-cognitive performance of rats. Since neither of these agonists affected significantly the choice accuracy, they do not appear to influence the working memory per se. The 5,7-DHT lesioned rats did not differ from their controls in response to these agonists. These results suggest that the combination of 5-HT1A receptor stimulation by 8-OH-DPAT and 5-HT2 receptor stimulation by DOI can interfere with the non-cognitive performance of rats in the DNMTP task. The results further indicate that the effect of 8-OH-DPAT may be mediated through post-synaptic rather than pre-synaptic 5-HT1A receptors.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed2000

Destruction and creation of spatial tuning by disinhibition: GABA(A) blockade of prefrontal cortical neurons engaged by working memory.

Local circuit neurons in the dorsolateral prefrontal cortex (dPFC) of monkeys have been implicated in the cellular basis of working memory. To further elucidate the role of inhibition in spatial tuning, we iontophoresed bicuculline methiodide (BMI) onto functionally characterized neurons in the dPFC of monkeys performing an oculomotor delayed response task. This GABA(A) blockade revealed that both putative interneurons and pyramidal cells possess significant inhibitory tone in the awake, behaving monkey. In addition, BMI application primarily resulted in the loss of previously extant spatial tuning in both cell types through reduction of both isodirectional and cross-directional inhibition. This tuning loss occurred in both the sensorimotor and mnemonic phases of the task, although the delay activity of prefrontal neurons appeared to be particularly affected. Finally, application of BMI also created significant spatial tuning in a sizable minority of units that were untuned in the control condition. Visual field analysis of such tuning suggests that it is likely caused by the unmasking of normally suppressed spatially tuned excitatory input. These findings provide the first direct evidence of directional inhibitory modulation of pyramidal cell and interneuron firing in both the mnemonic and sensorimotor phases of the working memory process, and they implicate a further role for GABAergic interneurons in the construction of spatial tuning in prefrontal cortex.

Action Potentials↗
PubMed2000

Collaborative activity between parietal and dorso-lateral prefrontal cortex in dynamic spatial working memory revealed by fMRI.

Functional MRI was used to determine how the constituents of the cortical network subserving dynamic spatial working memory respond to two types of increases in task complexity. Participants mentally maintained the most recent location of either one or three objects as the three objects moved discretely in either a two- or three-dimensional array. Cortical activation in the dorsolateral prefrontal (DLPFC) and the parietal cortex increased as a function of the number of object locations to be maintained and the dimensionality of the display. An analysis of the response characteristics of the individual voxels showed that a large proportion were activated only when both the variables imposed the higher level of demand. A smaller proportion were activated specifically in response to increases in task demand associated with each of the independent variables. A second experiment revealed the same effect of dimensionality in the parietal cortex when the movement of objects was signaled auditorily rather than visually, indicating that the additional representational demands induced by 3-D space are independent of input modality. The comodulation of activation in the prefrontal and parietal areas by the amount of computational demand suggests that the collaboration between areas is a basic feature underlying much of the functionality of spatial working memory.

Acoustic Stimulation↗
PubMed2006

The role of the rat prelimbic/infralimbic cortex in working memory: not involved in the short-term maintenance but in monitoring and processing functions.

Contrary to human and primate, working memory in the rodent is usually considered as a simple short term memory buffer and mainly investigated using delayed response paradigms. The aim of the present study was to further investigate the role of the rat prelimbic/infralimbic cortex in different spatial delayed tasks in order to dissociate its involvement in temporary storage from other information processes, such as behavioral flexibility and attention. In experiment 1 rats were trained in a standard elimination win-shift task in a radial-arm maze after which a 1-min delay was inserted mid trial. Prelimbic/infralimbic lesions induced only a transient disruption of performance following introduction of the delay. In experiment 2, rats were trained directly in a win-shift task with a 5-min delay that was subsequently extended to 30 min. Prelimbic/infralimbic lesions did not significantly affect behavior. Nevertheless, transient disruptions of performance (correlated with lesion extent) were noted repeatedly in lesioned rats when sets of interfering events were presented. The present findings indicate that prelimbic/infralimbic cortex is not directly involved in the short term maintenance of specific information but is implicated when changes, such as sudden introduction of a delay or exposure to unexpected interfering events, alter the initial situation. It appears that working memory in rodents should be considered, as in humans and primates, to encompass both storage and monitoring functions. The present results along with previous ones strongly suggest that prelimbic/infralimbic cortex is not involved in the temporary on-line storage but rather in the control of information required to prospectively organize the ongoing action.

Animals↗
PubMed1982

A multiple choice apparatus for electrophysiological investigations of spatial working memory in rats.

A multiple choice apparatus, minimizing the rat's movements and thus simplifying brain stimulation and/or recording in working memory experiments, consists of a dodecagonal enclosure (30 cm diameter, 100 cm high) with a horizontal platform assuming either an upper or a lower position, 43 or 65 cm below the top of the wall, respectively. The platform is moved between these two levels by a pneumatic system controlled by solid-state programming circuits. Each wall segment contains a choice window, 7 cm above the upper floor level, providing access to a recessed feeder. When the platform with a food-deprived rat moves into the upper position, the animal opens the hinged shutter of one window and gets the pellet. Five seconds later, a self-locking relay marks the visited window and the floor descends to the low position where it remains for a predetermined interval (e.g. 20 s), until it is raised again. The above cycle repeats as a long as different windows are chosen. When a choice is directed to an already visited window (error), the floor returns to the low position at once. During one trial, the animal is allowed 12 choices and the number of errors (i.e. choices directed to already entered windows) is recorded. In spite of the great reduction of kinaesthetic and vestibular signals and the almost complete elimination of visual extramaze cues, the working memory performance is similar to that in analogous radial maze.

Animals↗
PubMed1996

Spatial working memory is preserved in rats treated with anabolic-androgenic steroids.

The effects of anabolic-androgenic steroid (AAS) compounds on spatial working memory were evaluated in male rats. Thirty days of administration of a high dose of three individual AAS compounds (17 alpha-methyltestosterone, methandrostenolone, or testosterone cypionate) had no effects on spatial memory or motivation as tested on a delayed non-match-to-sample radial arm maze task. Administration of these AAS compounds at doses within the human abuse range does not impair spatial working memory in rats.

Anabolic Agents↗
PubMed2004

Working memory and literacy as predictors of performance on algebraic word problems.

Previous studies on individual differences in mathematical abilities have shown that working memory contributes to early arithmetic performance. In this study, we extended the investigation to algebraic word problem solving. A total of 151 10-year-olds were administered algebraic word problems and measures of working memory, intelligence quotient (IQ), and reading ability. Regression results were consistent with findings from the arithmetic literature showing that a literacy composite measure provided greater contribution than did executive function capacity. However, a series of path analyses showed that the overall contribution of executive function was comparable to that of literacy; the effect of executive function was mediated by that of literacy. Both the phonological loop and the visual spatial sketchpad failed to contribute directly; they contributed only indirectly by way of literacy and performance IQ, respectively.

Child↗
PubMed2001

Working memory and updating processes in reading comprehension.

In this study, we examine the relation between reading comprehension ability and success in working memory updating tasks. Groups of poor and good comprehenders, matched for logical reasoning ability, but different in reading comprehension ability, were administered various updating tasks in a series of experiments. In the first experiment, the participants were presented with lists of words, the length of which (4-10 words) was unknown beforehand, and were required to remember the last 4 words in each series. In this task, we found a decrease in performance that was related to longer series and poor reading ability. In the second experiment, we presented lists of nouns referring to items of different sizes, in a task that simulated the selection and updating of relevant information that occurs in the on-line comprehension process. The participants were required to remember a limited, predefined number of the smallest items presented. We found that poor comprehenders not only had a poorer memory, but also made a greater number of intrusion errors. In the third and fourth experiments, memory load (number of items to be selected) and suppression request (number of potentially relevant items) were manipulated within subjects. Increases in both memory load and suppression requests impaired performance. Furthermore, we found that poor comprehenders produced a greater number of intrusion errors, particularly when the suppression request was increased. Finally, in a fifth experiment, a request to specify the size of presented items was introduced. Poor comprehenders were able to select the appropriate items, although their recall was poorer. Altogether, the data show that working memory abilities, based on selecting and updating relevant information and avoiding intrusion errors, are related to reading comprehension.

Adult↗
PubMed2005

Functional neuroanatomy of subcomponent cognitive processes involved in verbal working memory.

Recent research has used functional magnetic resonance imaging (fMRI) to examine brain regions related to specific subcomponent cognitive processes of verbal working memory, which include initial encoding of material, maintenance of the information over a brief delay interval, and later retrieval of the information. The present study examined each of these subcomponents in 14 healthy adults using a Sternberg verbal working memory task and fMRI. Group analysis revealed several brain regions active during all subcomponent processes, which included dorsolateral and ventrolateral prefrontal, parietal, hippocampal, and premotor cortex. Several other brain regions showed activation limited to specific subcomponent processes.

Adult↗
PubMed1999

Hippocampal involvement in spatial and working memory: a structural MRI analysis of patients with unilateral mesial temporal lobe sclerosis.

Forty-seven patients with unilateral temporal lobe epilepsy (TLE) were investigated on the Nine-Box Maze. The task was designed to compare working memory and spatial mapping theories of the functions of the hippocampus and provide measures of spatial, object, working, and reference memory. The results extended our previous findings in a larger group of patients. Spatial memory deficits across both working and reference memory conditions were found in patients with a right epileptogenic focus. There was no evidence of an object working memory deficit, but a nonlateralized impairment in object reference memory was revealed, which is consistent with our previous findings. The pattern of results was confirmed in a subgroup of 33 patients with unilateral atrophy localized to the hippocampus and parahippocampal gyrus, as verified by volumetric analysis of magnetic resonance images. In addition spatial memory errors significantly correlated with volumetric measures of mesial temporal lobe structures and not with measures of the remaining temporal cortex. In contrast, object reference memory errors correlated with volumetric measures of the temporal cortex and not with mesial temporal lobe structures. These findings support a specialized role for the right hippocampal region in spatial memory.

Adult↗
PubMed1993

Chronic nicotinic stimulation and blockade effects on working memory.

Acute and chronic nicotine treatment has been found to improve learning and memory function in a variety of tasks. In several studies we have found that chronic nicotine infusion improves working memory performance. Replicating these results, the current study showed that chronic nicotine treatment (12mg/kg/day) significantly improved working memory performance in the radial-arm maze. The nicotine effect did not diminish during the 2 weeks following withdrawal. The nicotine-induced improvement was eliminated when the nicotinic antagonist mecamylamine (3mg/kg/day) was given concurrently, suggesting that the nicotine effect was mediated via actions on the nicotinic receptor. Surprisingly, when this chronic dose of mecamylamine was given alone, it caused a transient improvement in choice accuracy during the first week of administration. This improvement subsequently became attenuated and was not evident at all by the third and fourth weeks of administration.

Journal Article↗