Posterior fossa lesion volume and slowed information processing in multiple sclerosis

The Sternberg Paradigm: Correcting Encoding Latencies in Visual and Auditory Test Designs

The Sternberg task is a widely used tool for assessing the working memory performance in vision and cognitive science. It is possible to apply a visual or auditory variant of the Sternberg task to query the memory load. However, previous studies have shown that the subjects' corresponding reaction times differ dependent on the used variant. In this work, we present an experimental approach that is intended to correct the reaction time differences observed between auditory and visual item presentation. We found that the subjects' reaction time offset is related to the encoding speed of a single probe item. After correcting for these individual encoding latencies, differences in the results of both the auditory and visual Sternberg task become non-significant, p=0.252. Thus, an equal task difficulty can be concluded for both variants of item presentation.

Computerized neuropsychological assessment devices in multiple sclerosis: A systematic review

Background:

The proliferation of computerized neuropsychological assessment devices (CNADs) for screening and monitoring cognitive impairment is increasing exponentially. Previous reviews of computerized tests for multiple sclerosis (MS) were primarily qualitative and did not rigorously compare CNADs on psychometric properties.

Objective:

We aimed to systematically review the literature on the use of CNADs in MS and identify test batteries and single tests with good evidence for reliability and validity.

Method:

A search of four major online databases was conducted for publications related to computerized testing and MS. Test–retest reliability and validity coefficients and effect sizes were recorded for each CNAD test, along with administration characteristics.

Results:

We identified 11 batteries and 33 individual tests from 120 peer-reviewed articles meeting the inclusion criteria. CNADs with the strongest psychometric support include the CogState Brief Battery, Cognitive Drug Research Battery, NeuroTrax, CNS-Vital Signs, and computer-based administrations of the Symbol Digit Modalities Test.

Conclusion:

We identified several CNADs that are valid to screen for MS-related cognitive impairment, or to supplement full, conventional neuropsychological assessment. The necessity of testing with a technician, and in a controlled clinic/laboratory environment, remains uncertain.

Preliminary evidence of the cerebellar role on cognitive performances in clinically isolated syndrome

BACKGROUND

Cerebellar and cognitive dysfunction can occur early in clinically isolated syndrome (CIS). Eye tracking is a reliable tool for the evaluation of both subtle cerebellar symptoms and cognitive impairment.

OBJECTIVES

To investigate the early cognitive profile using neuropsychological and ocular motor (OM) testing in CIS with and without cerebellar dysfunction with OM testing compared to healthy subjects (HS).

METHODS

Twenty-eight patients and 12 HC underwent OM and neuropsychological testing. Cerebellar impairment was defined by the registration of saccadic intrusions and/or at least 10% of dysmetria during ocular motor recording. Visually guided saccade (VGS), memory-guided saccade (MGS) and antisaccade (AS) paradigms were compared to neuropsychological assessments.

RESULTS

The group of patients with cerebellar dysfunction (n=16) performed worse on MGS latencies and error rates, and had worse working memory, executive function and information processing speed (IPS) z scores than patients without cerebellar dysfunction. IPS was correlated with the AS error rate in all patients and with the VGS error rate and the MGS final eye position ratio in cerebellar patients.

CONCLUSION

Eye tracking is a sensitive tool to assess cognitive and cerebellar dysfunctions in CIS. In CIS patients, cerebellar impairment is associated with working memory, executive functions and IPS slowness.

Mechanisms of automaticity and anticipatory control in fluid intelligence

The constructs of fluid (Gf) and crystalized (Gc) intelligence represent an early attempt to describe the mechanisms of problem solving in the vertebrate brain. Modern neuroscience demonstrates that problem solving involves interplay between the mechanisms of automaticity and anticipatory control, enabling nature's elegant solution to the challenges animals face in their environment. Studies of neural functioning are making clear the primary role of cortical-subcortical interactions in the manifestation of intelligent behavior in humans and other vertebrates. A tridimensional model of intelligent problem solving is explored, wherein the basal ganglia system (BGS) and cerebrocerebellar system (CCS) interact within large scale brain networks. The BGS and CCS work together to enable automaticity to occur. The BGS enables the organism to learn what to do through a powerful instrumental learning system. The BGS also regulates when behavior is released through an inhibitory system which is incredibly sensitive to context. The CCS enables the organism to learn how to perform adaptive behaviors. Internal cerebellar models enable gradual improvements in the quality of behavioral output. The BGS and CCS interact within large scale brain networks, including the dorsal attention network (DAN), ventral attention network (VAN), default mode network (DMN) and frontoparietal network (FPN). The interactions of these systems enable vertebrate organisms to develop a vast array of complex adaptive behaviors. The benefits and importance of developing clinical tests to measure the integrity of these systems is considered.

The clinico-radiological paradox of cognitive function and MRI burden of white matter lesions in people with multiple sclerosis: A systematic review and meta-analysis

BACKGROUND

Moderate correlation exists between the imaging quantification of brain white matter lesions and cognitive performance in people with multiple sclerosis (MS). This may reflect the greater importance of other features, including subvisible pathology, or methodological limitations of the primary literature.

OBJECTIVES

To summarise the cognitive clinico-radiological paradox and explore the potential methodological factors that could influence the assessment of this relationship.

METHODS

Systematic review and meta-analysis of primary research relating cognitive function to white matter lesion burden.

RESULTS

Fifty papers met eligibility criteria for review, and meta-analysis of overall results was possible in thirty-two (2050 participants). Aggregate correlation between cognition and T2 lesion burden was r = -0.30 (95% confidence interval: -0.34, -0.26). Wide methodological variability was seen, particularly related to key factors in the cognitive data capture and image analysis techniques.

CONCLUSIONS

Resolving the persistent clinico-radiological paradox will likely require simultaneous evaluation of multiple components of the complex pathology using optimum measurement techniques for both cognitive and MRI feature quantification. We recommend a consensus initiative to support common standards for image analysis in MS, enabling benchmarking while also supporting ongoing innovation.

Posterior fossa syndrome with a large inflammatory ponto-mesencephalic lesion

Demonstration of a posterior fossa syndrome (PFS) in a 32-year-old male patient with clinically isolated syndrome which subsequently developed into relapsing-remitting Multiple Sclerosis. The patient suffered from double vision, coordination problems including unsteady gait and atactic dysarthria, concentration difficulties, as well as adynamia and impaired decision making. The patient clinically presented a cerebellar and dysexecutive syndrome. Cerebral magnetic resonance imaging (MRI) revealed a contrast enhancing ponto-mesencephalic lesion with a volume of 4.8cm³. Neuropsychological tests showed pronounced executive dysfunctions, reduced visuoconstructive skills, attentional deficits, echolalia, and non-fluent speech production. After cortisone and plasmapheresis, the cerebellar syndrome improved but manual fine motor skills and executive dysfunctions persisted. After three months, symptoms remitted except for a slight gait imbalance. After six months, neuropsychological tests were normal except for a moderate attention deficit. MRI revealed a clear regression of the ponto-mesencephalic lesion to a volume of 2.4cm³ without contrast enhancement. This case report intends to provide an overview of the symptomatology and etiology of PFS and offers new insights into its pathomechanism demonstrating a pontine disconnection syndrome caused by a large demyelinating plaque.

Information processing speed in multiple sclerosis: Past, present, and future

BACKGROUND

Information processing speed (IPS) is a prevalent cognitive impairment in multiple sclerosis (MS).

OBJECTIVES

This review aims to summarize the methods applied to assess IPS in MS and its theoretical conceptualization. A PubMed search was performed to select articles published between 1 January 2004 and 31 December 2013, resulting in 157 articles included.

RESULTS

The majority (54%) of studies assessed IPS with heterogeneous samples (several disease courses). Studies often report controlling for presence of other neurological disorders (60.5%), age (58.6%), education (51.6%), alcohol history (47.8%), or use of steroids (39.5%). Potential confounding variables, such as recent relapses (50.3%), history of developmental disorders (19.1%), and visual problems (29.9%), were often neglected. Assessments used to study IPS were heterogeneous (ranging from simple to complex tasks) among the studies under review, with 62 different tasks used. Only 9.6% of articles defined the construct of IPS and 22.3% discussed IPS in relation to a theoretical model.

FUTURE DIRECTIONS

The challenges for the upcoming decade include clarification of the definition of IPS as well as its theoretical conceptualization and a consensus on assessment. Based on the results obtained, we propose a new theoretical model, the tri-factor model of IPS.

Clinical and imaging assessment of cognitive dysfunction in multiple sclerosis

In patients with multiple sclerosis (MS), grey matter damage is widespread and might underlie many of the clinical symptoms, especially cognitive impairment. This relation between grey matter damage and cognitive impairment has been lent support by findings from clinical and MRI studies. However, many aspects of cognitive impairment in patients with MS still need to be characterised. Standardised neuropsychological tests that are easy to administer and sensitive to disease-related abnormalities are needed to gain a better understanding of the factors affecting cognitive performance in patients with MS than exists at present. Imaging measures of the grey matter are necessary, but not sufficient to fully characterise cognitive decline in MS. Imaging measures of both lesioned and normal-appearing white matter lend support to the hypothesis of the existence of an underlying disconnection syndrome that causes clinical symptoms to trigger. Findings on cortical reorganisation support the contribution of brain plasticity and cognitive reserve in limiting cognitive deficits. The development of clinical and imaging biomarkers that can monitor disease development and treatment response is crucial to allow early identification of patients with MS who are at risk of cognitive impairment.

Processing speed versus working memory: contributions to an information-processing task in multiple sclerosis

Individuals with multiple sclerosis (MS) often experience cognitive impairments in information processing. However, the relative contributions of processing speed abilities and working memory abilities to information-processing tasks are not yet fully understood. The current study examined the extent to which processing speed and/or working memory abilities contributed to an information-processing task, the Keeping Track Task (KTT). Forty-nine individuals with MS were given tests to assess processing speed and working memory, as well as the KTT. Regression analyses indicated that in the MS group, processing speed abilities accounted for the majority of the explained variance in KTT performance. The findings suggest that processing speed plays a significant role on KTT performance in MS. Implications for cognitive rehabilitation treatments aimed at improving processing speed abilities in MS are discussed.

Is Sternberg’s Memory Scanning Task Really a Short-Term Memory Task?

Sternberg’s paradigm is currently viewed as a typical short-term memory task and is widely used to tap mnemonic capacities in neuroscience studies. However, Sternberg’s original procedure includes an experimental constraint – recalling the sequence of digits in order – which was not reused in the following studies. In previous research ( Corbin & Marquer, 2008 , 2009 ), we showed that the recall constraint has an impact on the quantitative results as well as on the strategies implemented. These findings led us to wonder whether the presence or absence of this simple experimental constraint could also affect the processes implemented in Sternberg’s task. In order to answer this question, we analyzed the relationships between the performance levels of 50 participants on Sternberg’s task on various well-known span tasks and on a classical visual search task. The results showed that, in the recall condition, Sternberg’s paradigm appears to be a verbal working memory task, whereas in the no-recall condition, the task appears to be a recognition task that involves visuospatial memory capacities. In this latter condition, the processes implemented may be more similar to those implemented in visual search tasks.

Detectability of multiple sclerosis lesions with 3T MRI: a comparison of proton density-weighted and FLAIR sequences

OBJECTIVE

Due to the high signal intensity of cerebrospinal fluid (CSF), proton density-weighted (PD-w) images with long repeat times (TR) may be less able to detect periventricular lesions in patients with multiple sclerosis (MS). However, we have found good detectability of MS lesions with PD-w using long TR at 3 Tesla (3 T). For this reason, the aim of this study was to prospectively investigate the detectability of MS lesions at 3 T in PD-w compared with fluid-attenuated inversion recovery (FLAIR) sequences.

PATIENTS AND METHODS

A total of 11 MS patients were examined by a 3T magnetic resonance (MR) scanner, and their MS lesions were prospectively analyzed on PD-w and FLAIR images by two evaluators; detectability was rated by a three-point scoring system. The Wilcoxon signed-rank test was used for comparisons, and the level of significance was P<0.05.

RESULTS

Significantly more lesions were detectable on PD-w images (P<0.001 for both evaluators). In particular, PD-w was superior to FLAIR for the detection of periventricular (P=0.001 and P=0.013 for each evaluator respectively) and infratentorial (P<0.001 for both evaluators) lesions.

CONCLUSION

This was the first study to compare FLAIR and PD-w with long TR at 3 T; it revealed that PD-w is superior for detecting infratentorial and even periventricular MS lesions, despite the higher signal intensity of CSF. This might be due to the high spin density of MS lesions, thus distinguishing them from the surrounding brain tissue. For this reason, double-echo T2-weighted sequences at 3T are recommended to improve the detectability of MS lesions.

Age-related changes in processing speed: unique contributions of cerebellar and prefrontal cortex

Age-related declines in processing speed are hypothesized to underlie the widespread changes in cognition experienced by older adults. We used a structural covariance approach to identify putative neural networks that underlie age-related structural changes associated with processing speed for 42 adults ranging in age from 19 to 79 years. To characterize a potential mechanism by which age-related gray matter changes lead to slower processing speed, we examined the extent to which cerebral small vessel disease influenced the association between age-related gray matter changes and processing speed. A frontal pattern of gray matter and white matter variation that was related to cerebral small vessel disease, as well as a cerebellar pattern of gray matter and white matter variation were uniquely related to age-related declines in processing speed. These results demonstrate that at least two distinct factors affect age-related changes in processing speed, which might be slowed by mitigating cerebral small vessel disease and factors affecting declines in cerebellar morphology.

Individual differences in Sternberg's memory scanning task

This study provides a new perspective on both the cognitive processes actually implemented and the effect of a simple experimental control - the recall constraint - in Sternberg's memory scanning task. These findings were highlighted by adopting a new approach based on the comparison of qualitative and quantitative results. The analysis of individual processing, on 72 adults, each participating in one of two experimental conditions (with or without sequence recall), highlighted a large variability in quantitative results as well as qualitative procedures. Based on the participants' retrospective verbalisations, two categories of strategies were identified: (1) the procedures used to memorize the sequence of digits, and (2) the procedures used to compare this sequence with the test digit, which includes strategies for coding the items and processes for searching them in memory. The analysis of the strategies shows that their frequencies of use depend not only on the experimental condition, but also on the participants, the level of task difficulty and the interaction between participants and level of difficulty. This variability questions the accuracy of Sternberg's mean model. Furthermore, this approach suggests some answers to the old debate concerning the exhaustive search pattern for the yes response. Indeed, our results show three types of strategies that can be identified according to the different models of search suggested in the literature. The "exhaustive" search, that would only be involved in the recall condition and only for some of the participants, the "self-terminating" search and the "immediate" strategy, which can be identified with a model of parallel search with limited resources. Thus our study suggests that the different search models are appropriate but depend on both the specific experimental conditions and participant's strategy. Our results should help to improve the interpretation of data collected with this paradigm in cognitive and neuroscientific studies of memory.

Examining the link between information processing speed and executive functioning in multiple sclerosis

Slowed information processing speed (IPS) is frequently reported in those with multiple sclerosis (MS), and at least 20% are compromised on some aspect of executive functioning also. However, any relationship between these two processes has not been examined. The Sternberg Memory Scanning Test, Processing Speed Index (WAIS-III), Delis Kaplan Executive Function System (D.KEFS), and Working Memory Index (WMS-III) were administered to 90 participants with MS. Their performance on the PSI was significantly below the normative scores but no deficits in memory scanning speed were evident. The initial response speed of the Sternberg and the PSI were more closely related to D.KEFS performance, particularly in timed tasks with a high cognitive demand (switching tasks). In contrast, memory scanning speed was related to working memory. This study reinforces the link between IPS and working memory in MS, and supports the suggestion that IPS is not a unitary construct.

Cerebellar Transcranial Direct Current Stimulation Impairs the Practice-dependent Proficiency Increase in Working Memory

How the cerebellum is involved in the practice and proficiency of non-motor functions is still unclear. We tested whether transcranial direct current stimulation (tDCS) over the cerebellum (cerebellar tDCS) induces after-effects on the practice-dependent increase in the proficiency of a working memory (WM) task (Sternberg test) in 13 healthy subjects. We also assessed the effects of cerebellar tDCS on visual evoked potentials (VEPs) in four subjects and compared the effects of cerebellar tDCS on the Sternberg test with those elicited by tDCS delivered over the prefrontal cortex in five subjects. Our experiments showed that anodal or cathodal tDCS over the cerebellum impaired the practice-dependent improvement in the reaction times in a WM task. Because tDCS delivered over the prefrontal cortex induced an immediate change in the WM task but left the practice-dependent proficiency unchanged, the effects of cerebellar tDCS are structure-specific. Cerebellar tDCS left VEPs unaffected, its effect on the Sternberg task therefore seems unlikely to arise from visual system involvement. In conclusion, tDCS over the cerebellum specifically impairs the practice-dependent proficiency increase in verbal WM.

Troubles cognitifs et sclérose en plaques rémittente : intérêt de leur détection précoce

INTRODUCTION

Cognitive impairment is frequent in relapsing remitting Multiple Sclerosis and is often diagnosed after disruption of occupational and social relations.

METHODS

We studied at baseline a homogeneous population of 32 RRMS patients, diagnosed for less than 5 years, with spontaneous memory complaints, and 20 controls. Sixteen patients were followed for 2 years, combining physical examination, neuropsychological tests, and brain MRI. Neuropsychological tests used evaluated memory capacities, attentional capacities, executive functions, language, and visuo-constructive praxis. Lesion load on brain MRI was measured with semi-automatic segmentation procedures and manual control.

RESULTS

Eighty percent of patients presented cognitive impairment, and this proportion was higher than that found in the literature. These disorders were more marked for verbal episodic memory, attention, and executive functions. Patients with brain MRI that initially fulfilled the Barkhof criteria and those with callous lesions had more memory disorders. No link between global T1 and T2 lesion loads and neuropsychological scores was found. A statistical link between posterior fossa lesions and attentional disorders was shown. In the longitudinal follow-up, patients had better performances in memory and attentional domains, and a lower number of cognitive domains with dysfunction for each patient. This improvement on neuropsychological tests, whereas EDSS levels were stable, underlined a possible test-retest effect.

CONCLUSION

During the initial phase of the disease, most of the relapsing remitting patients present a mild cognitive impairment. Early detection, therapeutic propositions, and recognition of disorders are necessary.

Memory performance in multiple sclerosis patients correlates with central brain atrophy

OBJECTIVE

To assess whole brain and central brain atrophy as well as their differential relation to memory, cognitive performance, fatigue, depression and quality of life in patients with relapsing-remitting multiple sclerosis (RRMS).

METHODS

A 3D flow compensated gradient recalled T1-weighted MRI was acquired in 45 RRMS patients. An automated analysis tool was used to calculate brain parenchymal fraction (BPF) and ventricular brain fraction (VF). All patients were assessed with neuropsychological tests focusing on memory and self-rating scales for depression, fatigue and quality of life. Age corrected partial correlations between brain atrophy, motor performance, psychological scales and test scores were calculated.

RESULTS

BPF correlated moderately (0.3 < or = r < 0.5) with duration of symptoms and disease, the Expanded Disability Status Scale (EDSS), the upper extremity motor performance, and with mental aspects of quality of life. VF correlated moderately with EDSS, upper and lower extremity motor performance and memory functions. Neither BPF nor VF correlated with fatigue and depression. Results of several cognitive tests correlated moderately with depression and fatigue, the Paced Auditory Serial Addition Test (PASAT) showing the largest correlation.

CONCLUSIONS

Memory performance shows a correlation with relative ventricular size in RRMS patients, indicating the strategic location of the ventricle system along the structures of the limbic system and its vulnerability in MS. The PASAT and several other cognitive tests show moderate correlations with depression and fatigue, arguing for an inter relation between the cognitive functioning and the emotional state of patients. However, this relation is independent of measurable brain atrophy.

Cognitive impairment and decline in different MS subtypes

This paper presents results of two studies conducted to investigate cognition in different MS subtypes. First, the results of a study that has previously been published will be discussed. This was a cross-sectional study with 108 relapsing-remitting (RR), 71 secondary progressive (SP), 55 primary progressive (PP) MS patients, and 67 healthy controls [S.C.J. Huijbregts, N.F. Kalkers, L.M.J. de Sonneville, V. de Groot, I.E.W. Reuling, C.H. Polman, Differences in cognitive impairment of relapsing-remitting, secondary and primary progressive MS. Neurology 63 (2004) 335-339]. The second study involved a follow-up assessment after 2 years and included 30 SPMS patients, 25 PPMS patients, and 33 controls. The Brief Repeatable Battery of Neuropsychological Tests (BRB-N) was used for all cognitive assessments. All patient groups demonstrated cognitive deficits compared to healthy controls. RRMS patients were less affected compared to patients with progressive MS subtypes on the Paced Auditory Serial Addition Task (PASAT) and the Symbol Digit Modalities Test (SDMT). These differences were attenuated after control for physical disability level as measured by the Expanded Disability Status Scale. RRMS and SPMS patients were more severely impaired than PPMS patients on the 10/36 Spatial Recall Task and Word List Generation. Results of the follow-up study indicated that both progressive MS subtypes showed a lack of improvement compared to controls on the PASAT and the SDMT, but not on the other tasks of the BRB-N, indicating that performance on tasks requiring multiple abilities concurrently, i.e. visuo-spatial ability and processing speed (SDMT) or working memory and processing speed (PASAT), is most likely to decline across time.