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PubMed2006

Visual working memory is impaired when the medial temporal lobe is damaged.

The canonical description of the role of the medial temporal lobes (MTLs) in memory is that short-term forms of memory (e.g., working memory [WM]) are spared when the MTL is damaged, but longer term forms of memory are impaired. Tests used to assess this have typically had a heavy verbal component, potentially allowing explicit rehearsal strategies to maintain the WM trace over the memory delay period. Here we test the hypothesis that the MTL is necessary for visual WM when verbal rehearsal strategies are difficult to implement. In three patients with MTL damage we found impairments in spatial, face, and color WM, at delays as short as 4 sec. Impaired memory could not be attributed to memory load or perceptual problems. These findings suggest that the MTLs are critical for accurate visual WM.

Aged↗
PubMed2000

Sex steroids modify working memory.

In the last ten years, numerous mechanisms by which sex steroids modify cortical function have been described. For example, estrogen replacement improves verbal memory in women, and animal studies have shown effects of estrogen on hippocampal synaptogenesis and function. Little is known about sex steroid effects on other aspects of memory, such as frontal lobe-mediated working memory. We examined the relationships between working memory and sex steroid concentrations and whether sex steroid supplementation would modify age-related loss of working memory in older men and women. Before hormone supplementation, working memory, tested with the Subject Ordered Pointing Test (SOP), was worse in older subjects than younger subjects, and there was no evidence of gender differences at either age. Testosterone supplementation improved working memory in older men, but a similar enhancement of working memory was not found in older women supplemented with estrogen. In men, testosterone and estrogen effects were reciprocal - with better working memory related to a higher testosterone to estrogen ratio. These results suggest that sex steroids can modulate working memory in men and can act as modulators of cognition throughout life.

Adult↗
PubMed2005

Cerebral activation patterns during working memory performance in multiple sclerosis using FMRI.

Working memory deficits are common in Multi Sclerosis (MS) and have been identified behaviourally in numerous studies. Despite recent advance in functional magnetic resonance imaging (fMRI), few published studies have examined cerebral activations associated with working memory dysfunction in MS. The present study examines brain activation patterns during performance of a working memory task in individual with clinically definite MS, compared to healthy controls (HC). fMRI was performed using a 1.5 Tesla GE scanner during a modified Paced Auditory Serial Addition Test (mPA-SAT). Participants were 6 individuals with MS with working memory impairment as evidenced on neuropsychological testing, 5 individuals with MS without working memory impairment, and 5 HC. Groups were demographically equivalent. Data were analyzed using Statistical Parametric Mapping (SPM99) software, with a stringent significance level (alpha < .005, voxel extent > or =8). Both MS groups and the HC group were able to perform the task, with comparable performance in terms of numbers of correct responses. Activation patterns within the HC and MS not-impaired groups were noted in similar brain regions, consistent with published observations in healthy samples That is, activations were lateralized to the left hemisphere, involving predominantly frontal regions. In contrast, the MS impaired group showed greater right frontal and right parietal lobe activation, when compared with the HC group. Thus, it appears that working memory dysfunction in MS is associated with altered patterns of cerebral activation that are related to the presence of cognitive impairement, and not solely a function of MS.

Acoustic Stimulation↗
PubMed2004

An overview of the tasks used to test working memory in rodents.

In rodents, working memory is a representation of an object, stimulus, or spatial location that is typically used within a testing session, but not between sessions, to guide behaviour. In this review we consider a number of the tasks used to assess this type of memory in the rodent, and highlight some of their limitations. Although the concept of working memory as applied to rodents has its origin in the experiments of David Olton and Werner Honig in the 1970s, many earlier experiments assessed the same type of memory under the guise of delayed reaction or alternation paradigms. We revisit these early tasks, and also consider the nature of working memory used on maze tasks, operant box based tasks, and non-spatial delayed non-matching to sample paradigms.

Animals↗
PubMed2005

Background-activity-dependent properties of a network model for working memory that incorporates cellular bistability.

In models of working memory, transient stimuli are encoded by feature-selective persistent neural activity. Network models of working memory are also implicitly bistable. In the absence of a brief stimulus, only spontaneous, low-level, and presumably nonpatterned neural activity is seen. In many working-memory models, local recurrent excitation combined with long-range inhibition (Mexican hat coupling) can result in a network-induced, spatially localized persistent activity or "bump state" that coexists with a stable uniform state. There is now renewed interest in the concept that individual neurons might have some intrinsic ability to sustain persistent activity without recurrent network interactions. A recent visuospatial working-memory model (Camperi and Wang 1998) incorporates both intrinsic bistability of individual neurons within a firing rate network model and a single population of neurons on a ring with lateral inhibitory coupling. We have explored this model in more detail and have characterized the response properties with changes in background synaptic input I(o) and stimulus width. We find that only a small range of I(o) yields a working-memory-like coexistence of bump and uniform solutions that are both stable. There is a rather larger range where only the bump solution is stable that might correspond instead to a feature-selective long-term memory. Such a network therefore requires careful tuning to exhibit working-memory-like function. Interestingly, where bumps and uniform stable states coexist, we find a continuous family of stable bumps representing stimulus width. Thus, in the range of parameters corresponding to working memory, the model is capable of capturing a two-parameter family of stimulus features including both orientation and width.

Action Potentials↗
PubMed2006

Visual working memory depends on attentional filtering.

Working memory holds information actively being used in cognitive performance. Two important aspects of working memory are how many items it can hold, and how efficiently it can be used. Recently, Vogel and colleagues used event-related brain potentials to show that these two things are related. People who could remember more objects from a spatial array also more efficiently excluded irrelevant objects. The results raise important questions about what aspect of working memory is most fundamental.

Attention↗
PubMed2005

Under the curve: critical issues for elucidating D1 receptor function in working memory.

It has been postulated that spatial working memory operates optimally within a limited range of dopamine transmission and D1 dopamine receptor signaling in prefrontal cortex. Insufficiency in prefrontal dopamine, as in aging, and excessive transmission, as in acute stress, lead to impairments in working memory that can be ameliorated by D1 receptor agonist and antagonist treatment, respectively. Iontophoretic investigations of dopamine's influence on the cellular mechanisms of working memory have revealed that moderate D1 blockade can enhance memory fields in primate prefrontal pyramidal neurons while strong blockade abolishes them. The combined behavioral and physiological evidence indicates that there is a normal range of dopamine function in prefrontal cortex that can be described as an "inverted-U" relationship between dopamine transmission and the integrity of working memory. Both in vivo and in vitro studies have demonstrated a role for dopamine in promoting the excitability of prefrontal pyramidal cells and facilitating their N-methyl-d-aspartate inputs, while simultaneously restraining recurrent excitation and facilitating feedforward inhibition. This evidence indicates that there is a fine balance between the synergistic mechanisms of D1 modulation in working memory. Given the critical role of prefrontal function for cognition, it is not surprising that this balancing act is perturbed by both subtle genetic influences and environmental events. Further, there is evidence for an imbalance in these dopaminergic mechanisms in multiple neuropsychiatric disorders, particularly schizophrenia, and in related nonhuman primate models. Elucidating the orchestration of dopamine signaling in key nodes within prefrontal microcircuitry is therefore pivotal for understanding the influence of dopamine transmission on the dynamics of working memory. Here, we explore the hypothesis that the window of optimal dopamine signaling changes on a behavioral time-scale, dependent upon current cognitive demands and local neuronal activity as well as long-term alterations in signaling pathways and gene expression. If we look under the bell-shaped curve of prefrontal dopamine function, it is the relationship between neuromodulation and cognitive function that promises to bridge our knowledge between molecule and mind.

Animals↗
PubMed2002

Verbal and spatial working memory performance among HIV-infected adults.

Subtypes of working memory performance were examined in a cohort of 50 HIV-infected adults and 23 uninfected controls using an n-back paradigm (2-back) in which alphabetic stimuli were quasi-randomly presented to a quadrant of a computer monitor. In the verbal working memory condition, participants determined whether each successive letter matched the letter that appeared two previously in the series, regardless of spatial location. In the spatial working memory condition, participants determined whether each letter matched the spatial location of the letter that had appeared two previously, regardless of letter identity. The dependent variable was percent accuracy in each condition. Results of mixed model ANOVA revealed that the HIV-infected participants performed significantly worse than controls on both the verbal and spatial working memory tasks. A significant main effect for working memory condition was also present with both participant groups performing better on the spatial working memory task. These results, the first study of HIV-infected adults to directly compare verbal versus spatial working memory performance using the identical test stimuli across task conditions, suggests that HIV infection is associated with a decrement in working memory efficiency that is equally apparent for both verbal and spatial processing. These findings implicate central executive dysfunction as a likely substrate and provide the basis for hypothesizing that decline in working memory may contribute to other HIV-associated neuropsychological deficits.

Adult↗
PubMed1989

The development of working memory in normally achieving and subtypes of learning disabled children.

Working memory has been proposed as an important component of reading and arithmetic skills. The development of working memory was studied in normally achieving and subtypes of learning disabled children. The performance of reading disabled (RD), arithmetic disabled (ARITHD), and attentional deficit disordered (ADD) children, age 7-13, was compared to normal achievers (NA) on 2 working memory tasks, 1 involving sentences and the other involving counting. There was a significant growth of working memory as a function of age. In addition, the RD children had significantly lower scores on both tasks. The ARITHD children had significantly lower scores only on the Working Memory--Counting task, and the ADD group had scores similar to the normally achieving children except at the youngest age level in the Working Memory--Sentences task. Thus, a reading disability appears to involve a generalized deficit in working memory. Children with an arithmetic disability do not have a generalized language deficit but have a specific working memory deficit in relation to processing numerical information. As children with ADD did not have deficits in these tasks, working memory may not have significant attentional components. An important component of the development of reading and computational arithmetic skills appears to be the growth of working memory for language and numerical information.

Achievement↗
PubMed2001

Aging and interference in verbal working memory.

According to inhibitory views of working memory, old adults should have particular problems deleting irrelevant information from working memory, leading to greater interference effects compared with young adults. The authors investigated this hypothesis by using variations of an A-B, C-D retroactive interference paradigm in working memory with young and old adults. They used a recognition measure of memory, assessing both accuracy and reaction time. The primary finding was that senior adults consistently exhibited proportionally greater retroactive interference effects compared with young adults when interfering word pairs that had been read aloud had to be rejected. Patterns of recognition and reaction time data suggested that old adults' activation of target material is similar to young adults, but they experience sustained activation of irrelevant material that has entered working memory. Theoretical implications of these findings for inhibitory deficit (R. T. Zacks & L. Hasher, 1998) and source memory deficit accounts of cognitive aging are discussed.

Adult↗
PubMed2000

Auditory working memory and verbal recall memory in schizotypy.

Deficits on verbal memory tasks, as well as on spatial and auditory working memory tasks, have been observed in schizophrenia patients. A useful strategy in the determination of the premorbid indicator status of specific cognitive and memory deficits observed in patients is to examine those persons at increased biological risk for schizophrenia (e.g. first-degree relatives), schizotypal personality disorder patients, and/or psychometrically identified schizotypes for comparable deficits, though perhaps less profound than those seen in actual patients. We examined verbal memory and auditory working memory functioning in 31 schizotypic and 26 normal control subjects from a large randomly ascertained non-clinical university population. Schizotypy status was determined psychometrically using the well-known Perceptual Aberration Scale. Contrary to our theory-guided expectations, noteworthy deficits in verbal memory and auditory working memory were not observed in the schizotypic subjects and the two experimental groups did not differ significantly on any of the memory measures. These results were discussed in light of prior results obtained using the spatial delayed response task (i.e. spatial working memory) and Wisconsin Card Sorting Test performance on these same subjects. The theoretical implications of these findings are discussed in relation to the putative processes involved in the working memory system, as well as in relation to the schizotypy construct.

Adult↗
PubMed2006

Nonvisual codes and nonvisual brain areas support visual working memory.

Systems models hold working memory to depend on specialized, domain-specific storage buffers. Here, however, we demonstrate that short-term retention of the identity or location of visually presented stimuli is disrupted by nonvisual secondary tasks performed in the dark-passive listening to nouns or endogenous generation of saccades, respectively. This indicates that the short-term retention of visual information relies on multiple mental codes, some of them nonvisual. Event-related functional magnetic resonance imaging (fMRI) reveals the neural correlates of these interference effects to be more complex and more regionally specific than previously described. Although nonspecific dual-task effects produce a generalized decrease of task-evoked fMRI response across many brain regions, the interference-specific effect is a relative increase of activity localized to regions associated with the secondary task in question: left hemisphere perisylvian cortex in the case of passive listening distraction and frontal oculomotor regions in the case of saccadic distraction. Within these regions, the neural interference effects are specific to voxels that show delay-period activity on unfilled memory trials. They also predict individual differences in the magnitude of the behavioral interference effect. These results indicate that nonvisual processes supported by nonvisual brain areas contribute importantly to "visual" working memory performance.

Adult↗
PubMed2000

Schizophrenic subjects show aberrant fMRI activation of dorsolateral prefrontal cortex and basal ganglia during working memory performance.

BACKGROUND: Working memory (WM) deficits in schizophrenia have been associated with dorsolateral prefrontal cortex (DLPFC) dysfunction in neuroimaging studies. We previously found increased DLPFC activation in schizophrenic versus normal subjects during WM performance (Manoach et al 1999b). We now have investigated whether schizophrenic subjects recruit different brain regions, particularly the basal ganglia and thalamus, components of frontostriatal circuitry thought to mediate WM. METHODS: We examined regional brain activation in nine normal and nine schizophrenic subjects during WM performance using functional magnetic resonance imaging. Subjects performed a modified version of the Sternberg Item Recognition Paradigm that included a monetary reward for correct responses. We compared high and low WM load conditions to each other and to a non-WM baseline condition. We examined activation in both individual subjects and averaged group data. RESULTS: Relative to normal subjects, schizophrenic subjects exhibited deficient WM performance, at least an equal magnitude of right DLPFC activation, significantly greater left DLPFC activation, and increased spatial heterogeneity of DLPFC activation. Furthermore, only the schizophrenic group activated the basal ganglia and thalamus, even when matched for task performance with the normal group. CONCLUSIONS: Aberrant WM performance and brain activation in schizophrenia may reflect dysfunction of frontostriatal circuitry that subserves WM. Future studies will elucidate the contribution of the anatomical components of this circuitry to WM deficits.

Adult↗
PubMedDate not supplied

Language representation and working memory with bilinguals.

Working memory (WM) plays a crucial role in learning a second language (L2). The ability to repeat words in an unknown language has been observed to predict success in learning that language. Conversely, decreased digit span and inability to repeat pseudowords have been related with failure in L2 acquisition. Not only digit span, but also "word span" and "semantic span" should be considered in WM analysis. In addition to the phonological system, a semantic system is proposed in the WM model for language. In bilinguals, brain activation patterns during WM tasks have been observed to be more complex when using a L2. Processing information in L2 is more demanding, and WM may be less efficient. It can be conjectured that language understanding defects in L2 are at least partially due to this decreased efficiency of WM in its phonological as well as in its semantic subsystem. The reader will be introduced to the basic assumptions of WM. It will be emphasized that WM is significantly involved in the ability to learn a L2. Cross-linguistic differences in digit span will be analyzed. It will be concluded that despite digit span and word span are affected by different variables, "semantic span" may be similar across languages. Words in a L2 function as low frequency words, and hence, semantic search takes longer and WM is less efficient. It will be concluded that in addition to the "phonological system," the WM model should include a "semantic system," involving a "semantic store" and a "semantic search" process.

Humans↗
PubMed2005

Neural system for controlling the contents of object working memory in humans.

Working memory (WM), the active maintenance of currently relevant information, is a flexible system allowing for fast and frequent goal-directed changes of rehearsed information. Successful WM maintenance prevents interference from distracting stimuli while allowing new task-relevant information to update the contents of WM. We used functional magnetic resonance imaging to show that when WM contents were updated, regardless of stimulus type (faces or houses), a frontoparietal network showed transient increases in activation. Some of these regions are highly similar to those identified in studies of shifting attention, supporting the idea that updating WM involves a change in the attentional priority afforded to the current perceptual input. A region within the mid-ventrolateral prefrontal cortex, near the junction of the inferior frontal sulcus and precentral sulcus (inferior frontal junction), that has previously been implicated in cognitive control, demonstrated transient increases in activity during updating as well as sustained maintenance activity. A more anterior prefrontal region, middle frontal gyrus, previously implicated in protecting the contents of WM from interfering stimuli during maintenance, demonstrated transient increases in activity during updating. The current study suggests that updating WM results from a combination of increased attention to the visual stimulus and a change in the system's interference protection state.

Adult↗
PubMed2004

Visual encoding differentially affects auditory event-related potentials during working memory retrieval.

Previous working memory studies using auditory stimuli at both encoding and retrieval show amplitude decreases in event-related potentials (N100 and late positive wave, LPW) at retrieval as a function of memory load. This study tested if these effects are associated with phonological or semantic coding by presenting visual stimuli at encoding and auditory stimuli at retrieval. We hypothesized that event-related potentials associated with phonological but not semantic coding would be affected by modality differences at encoding and retrieval. Memory sets having one, three, or five visual digits were followed by auditory probes that subjects classified as present or absent from the set. Reaction time increased and LPW amplitudes decreased with increases in memory load, but there were no significant effects of memory load on N100 amplitude. Results suggest that with respect to brain activity that covaries with memory load, probe N100 amplitude is associated with phonological coding and LPW amplitude is associated with semantic coding.

Acoustic Stimulation↗
PubMed2004

The role of spatial working memory in visual search efficiency.

Many theories have proposed that visual working memory plays an important role in visual search. In contrast, by showing that a nonspatial working memory load did not interfere with search efficiency, Woodman, Vogel, and Luck (2001) recently proposed that the role of working memory in visual search is insignificant. However, the visual search process may interfere with spatial working memory. In the present study, a visual search task was performed concurrently with either a spatial working memory task (Experiment 1) or a nonspatial working memory task (Experiment 2). We found that the visual search process interfered with a spatial working memory load, but not with a nonspatial working memory load. These results suggest that there is a distinction between spatial and nonspatial working memory in terms of interactions with visual search tasks. These results imply that the visual search process and spatial working memory storage require the same limited-capacity mechanisms.

Exploratory Behavior↗
PubMed2006

On the causal mechanisms of stereotype threat: can skills that don't rely heavily on working memory still be threatened?

Recent work suggests that stereotype threat (ST) harms performance by reducing available working memory capacity. Is this the only mechanism by which ST can occur? Three experiments examined ST's impact on expert golf putting, which is not harmed when working memory is reduced but is hurt when attention is allocated to proceduralized processes that normally run outside working memory. Experiment 1 showed that well learned golf putting is susceptible to ST. Experiments 2 and 3 demonstrated that giving expert golfers a secondary task eliminates ST-induced impairment. Distracting attention away from the stereotype-related behavior eliminates the harmful impact of negative stereotype activation. These results are consistent with explicit monitoring theories of choking under pressure, which suggest that performance degradation can occur when too much attention is allocated to processes that usually run more automatically. Thus, ST alters information processing in multiple ways, inducing performance decrements for different reasons in different tasks.

Adult↗