Memory Capacity In MS

We used event-related Functional MRI to investigate the Neural bases of two categories of mental processes believed to contribute to performance of an alphabetization Working Memory task: Memory Storage and Memory Manipulation.

Our Delayed-Response Tasks required Memory for the identity and position-in-the-display of items in two- or five-letter Memory sets.

To identify load-sensitive regions) or Memory for the identity and relative position-in-the-alphabet of items in five-letter Memory sets (to identify manipulation-sensitive regions).

Results revealed Voxels (volume elements) in the Left PeriSylvian Cortex of five of five subjects showing load sensitivity (as contrasted with alphabetization-sensitive Voxels in this region in only one subject).

And Voxels of DorsoLateral PreFrontal Cortex in all subjects showing alphabetization sensitivity (as contrasted with load-sensitive Voxels in this region in two subjects). This double dissociation was reliable at the group level.

These data are consistent with the hypothesis that the NonMnemonic Executive Control processes that can contribute to Working Memory function are primarily PreFrontal Cortex-mediated.

Whereas Mnemonic processes necessary for Working Memory storage are primarily Posteriorly mediated.

More broadly, they support the view that Working Memory is a faculty that arises from the coordinated interaction of computationally and NeuroAnatomically dissociable processes.

Recent research has shown that Depression in Multiple Sclerosis (MS) is associated with deficits on Cognitively demanding tasks.

One explanation for this relationship is that depressed MS patients may have reduced Working Memory Capacity. The present study was designed to test this hypothesis.

Depressed MS patients were compared with NonDepressed MS patients and NonDepressed healthy controls on a task of Working Memory Capacity (Reading Span) and a Short-Term Memory task not taxing Working Memory Capacity (Word Span).

In support of the Capacity-Reduction model, compared with the NonDepressed groups, Depressed MS patients performed significantly worse on Reading Span (p<.001) but not on word span.

Additionally, Reading Span was significantly correlated with Capacity-Demanding Tasks shown to be impaired in Depressed MS patients in previous reports.

Results suggest that Depressed MS patients are characterized by limited Working Memory Capacity and that the Central Executive component of the Working Memory System may be most affected.

Because it is theorized that Depression results in reduced available Attentional Capacity that, in turn, can explain the impaired performance on Capacity-Demanding Tasks in Depressed individuals.

The authors predicted that Multiple Sclerosis (MS) patients with Depressed Mood would have difficulty with these types of tasks.

Twenty Depressed Mood MS participants were compared with 41 nonDepressed Mood MS participants and 8 nonDepressed Mood controls on 5 Attentional Capacity-Demanding Clinical Memory and Attentional Tasks and 3 tasks with Minimal Capacity Demands.

Depressed Mood MS patients performed significantly worse than both nonDepressed Mood groups on the 3 speeded Capacity-Demanding Attentional Measures.

But not on any of the tasks requiring few Capacity Demands, supporting the authors' predictions.

The possibility that the impaired performance of Depressed Mood MS patients on Speeded Attentional Tasks was mediated by reduced Verbal Working Memory Capacity, impaired deployment of Executive Strategies that access Working Memory Capacity, or PsychoMotor slowing is explored.

The causes of the positive relationship between Comprehension and measures of Working Memory Capacity remain unclear.

This study tests three hypotheses for the relationship by equating the difficulty, for 48 individual subjects, of processing demands in Complex Working Memory tasks.

Even with difficulty of processing equated, the relationship between number of words recalled in the Working Memory measure and Comprehension remained high and significant. The results favor a general capacity view.

We suggest that high Working Memory Span subjects have more limited-capacity attentional resources available to them.

Than Low Span subjects, and that individual differences in Working Memory Capacity will have implications for any task that requires Controlled Effortful Processing.

This study investigated the relationship between Working Memory Capacity and Reading Comprehension in Aphasia.

A measurement of Working Memory Capacity was obtained using a modified version of Daneman and Carpenter's (1980) Reading Span Task.

Sets of sentences ranging in length from one to six words were presented to 22 Aphasic subjects who were required to retain the terminal words following each sentence for subsequent recognition.

The maximum number of words retrieved was used as an index of Working Memory Capacity. Two versions of the task (Listening and Reading) were presented depending on the subjects' ability to read.

Strong positive correlations were found between Working Memory Capacity, Reading Comprehension, and Langague Function.

These results support the notion that the ability of Aphasic individuals to comprehend language is predictable from their Working Memory Capacities.

Copyright 1998 Academic Press.

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.

We examined Short-Term Memory (STM) among a group of 23 definite, Chronic/Progressive Multiple Sclerosis (MS) patients.

All of whom had experienced recent significant disease activity, and a control group matched closely on age and education. MS patients were impaired, relative to controls, on the majority of the measures used.

Although there were no significant differences between groups on the Mini Mental State Examination, patients performed more poorly on digits forward and backward, the Brown-Peterson test, and the Logical Memory Scale of the Revised Wechsler Memory Scale (both immediate and delayed).

Performance on tests sensitive to Central Processing Capacity was significantly correlated with measures of STM. Working Memory was significantly impaired in this sample of Chronic/Progressive MS patients.

In conjunction with previous research showing Deficient Information Processing and PreFrontal Dysfunction among this population.

The findings suggest that an Impairment Of Central Information Processing may be a fundamental aspect of the Mnestic and Cognitive Decline observed in many Chronic/Progressive MS patients.

Background
Recently, the P600 component of Event Related Potentials, a waveform that is conceived to be generated and/or modulated by Basal Ganglia and Cingulate Area has been considered an index of the completion of any synchronized operation after target detection, having much in common with Working Memory operation.

Moreover, dysfunction of these Brain structures as well as Working Memory deficits have been implicated in the pathophysiology of Multiple Sclerosis.

The aim of this study was to investigate the patterns of P600 elicited during a Working Memory test in Multiple Sclerosis patients compared with healthy controls.

Methods
Twenty two definite, Chronic/Progressive Multiple Sclerosis patients, with recent exacerbation of their illness, and 20 normal subjects matched for age, sex, and educational level, were studied with a computerized version of the digit span test of Wechsler batteries.

Auditory P600 were measured during the anticipatory period of this test.

Results
The patient group, as compared with healthy controls, showed significantly reduced latencies of P600 at Left Frontal Areas and reduced P600 amplitudes at Left TemporoParietal Region.

Moreover, Memory performance of patients was significantly more impaired when compared with healthy controls.

Conclusions
These findings may indicate that Multiple Sclerosis is associated with abnormal features of the completion of synchronized operation after target detection, as they are reflected by P600 amplitudes and latencies.

Dysfunction of this mechanism may contribute to the identification of basic Cognitive processes that could account for the Cognitive Deficits in Multiple Sclerosis.

Objective
Cognitive Dysfunctions may contribute to limitation of everyday activities of patients with Multiple Sclerosis (MS).

Recent studies have demonstrated that 45 to 65% of MS-patients are Cognitively Impaired.

The profile of MS-related Cognitive Dysfunctions varies greatly. It includes Memory and Learning deficits, Attention deficits, Executive dysfunctions and Visuo-Spatial deficits.

Most studies of Cognition in MS examined patients in later stages, often including MS-patients with marked physical disabilities.

Studies of Cognitive Dysfunctions in the early stage of the disease are rare.

This study specifically aimed at evaluating and characterizing Cognitive Impairments in the early stage of MS, and determining specific patterns of Cognitive Dysfunction.

Methods
21 MS patients, experiencing their first Neurological symptoms not more than two years previously, and 22 healthy controls were compared.

A comprehensive NeuroPsychological test-battery was used to evaluate MS-related Cognition.

The battery consisted of Memory and Learning tests, Executive functioning tests and a Visuo Spatial functioning test.

A computerized Attention test-battery was also included, which assess accuracy and speed of test responses. In addition Depression and intellectual capabilities were assessed.

Results
Compared with healthy controls, MS-patients in the early stage of the disease performed significantly lower on each NeuroPsychological assessment, except for Verbal Short-Term Memory.

In particular, MS-patients showed a lengthened reaction time for Simple and Focused Attention (19-38%), impaired Non-Verbal Memory function (RVDLT recognition: 33%) and a Planning deficit (24%).

Associations between Information Processing Speed and disease course and the employment situation were additionally found.

However, patients did not have clinically relevant Depression rates on the ADS-L and Visuo Spatial abilities remain preserved.

Conclusion
Our findings revealed discrete Cognitive Dysfunction in MS-patients within the early stage of the disease.