La mémoire de travail dans la sclérose en plaques : revue de la littérature

Executive functions in relapsing-remitting multiple sclerosis

Some studies suggest that patients with relapsing-remitting multiple sclerosis have problems in the functioning of working memory, and more specifically in executive functions, but the available results are still inconsistent. The aim of the present study was to examine executive functioning in multiple sclerosis using classical and representative tasks for divided attention, updating, attentional shifting, and inhibition. The sample was composed of 48 participants aged between 18 and 59 years (24 persons living with multiple sclerosis and 24 healthy participants matched in age and education level). The executive functions of divided attention, updating, attentional shifting, and inhibition were analyzed through the Dual-Task Paradigm, the N-Back task, the Trail Making Test (TMT), and the Stroop test, respectively. The analyses of the data showed that the functioning of working memory was impaired in multiple sclerosis in the executive functions of divided attention and updating when the group of persons living with MS and the control group were compared. In addition, the performance in the four executive functions analyzed did not show the same profile across the persons living with MS in the sample, as no deficit in attentional shifting or inhibition was observed. It can be concluded that the presence of deficits was observed only in the executive functions of divided attention and updating under the condition of greater cognitive demand. The clinical implications of these results are underlined due to their impact on daily life.

Memory improvement in multiple sclerosis after an extensive cognitive rehabilitation program in groups with a multicenter double-blind randomized trial

OBJECTIVE

The aim of this study is to determine the effectiveness of an extended cognitive rehabilitation program in group's sessions in multiple sclerosis.

DESIGN

Double-blind multicenter randomized trial.

PARTICIPANTS

People with multiple sclerosis of 18 to 60 years, Expanded Disability Status Scale ⩽6.0, mild to moderate cognitive impairment.

INTERVENTIONS

They were randomized into cognitive rehabilitation program (ProCog-SEP) or in a placebo program. ProCog-SEP comprises 13 group's sessions over 6 months and includes psychoeducational advices and cognitive exercises. Placebo program included non-cognitive exercises. No strategy and no cognitive advice were provided.

MAIN MEASURES

The primary endpoint was the percentage of verbal memory learning measured by the Selective Reminding Test. A comprehensive neuropsychological assessment is carried out before and after interventions by a neuropsychologist blinded to intervention. Effectiveness of the ProCog-SEP versus Placebo has been verified using linear regression models.

RESULTS

In total, 128 participants were randomized and 110 were included in the study after planning session in groups; 101 completed this trial (77.2% females); mean age: 46.1 years (±9.6); disease duration: 11.8 years (±7.5). ProCog-SEP was more effective in increasing in learning index (9.21 (95% confidence interval (CI): 1.43, 16.99); p = 0.02) and in working memory on manipulation (0.63 (95% CI: 0.17, 1.09); p = 0.01), and updating capacities (-1.1 (95% CI: -2.13, -0.06); p = 0.04). No difference was observed for other neuropsychological outcomes. Regarding quality of life outcomes, no change was observed between the two groups.

CONCLUSION

These findings suggest that ProCog-SEP could improve verbal learning abilities and working memory in people with multiple sclerosis. These improvements were observed with 13 group sessions over 6 months.

Cognitive Fatigue, Sleep and Cortical Activity in Multiple Sclerosis Disease. A Behavioral, Polysomnographic and Functional Near-Infrared Spectroscopy Investigation

Patients with multiple sclerosis (MS) disease frequently experience fatigue as their most debilitating symptom. Fatigue in MS partially refers to a cognitive component, cognitive fatigue (CF), characterized by a faster and stronger than usual development of the subjective feeling of exhaustion that follows sustained cognitive demands. The feeling of CF might result from supplementary task-related brain activity following MS-related demyelination and neurodegeneration. Besides, CF in MS disease might also stem from disrupted sleep. The present study investigated the association between the triggering of CF, task-related brain activity and sleep features. In a counterbalance mixed design, 10 patients with MS and 11 healthy controls were exposed twice for 16 min to a CF-inducing dual working memory updating task (TloadDback) under low or high cognitive demands conditions, counterbalanced. Considering known inter-individual differences and potential cognitive deficits in MS, the maximal cognitive load of the task was individually adapted to each participant’s own upper limits. During the experimental sessions, cortical brain activity was measured using near-infrared spectroscopy (NIRS) during the CF-induction task, and in a resting state immediately before and after. Ambulatory polysomnography recordings were obtained on the nights preceding experimental sessions. When cognitive load was individually adapted to their processing capabilities, patients with MS exhibited similar than healthy controls levels of subjectively perceived CF, evolution of performance during the task, and brain activity patterns. Linear mixed models indicate a negative association between oxygenation level changes in the dorsolateral prefrontal cortex (DLPFC) and the triggering of subjective CF in patients with MS only. Longer total sleep time was also associated with higher CF in MS patients. These results suggest that controlling for cognitive load between individuals with and without MS results in a similar task-related development of subjective CF. Besides comparable performance and cortical brain activity between groups, mixed model analyses suggest a possible association between CF, DLPFC activity and sleep duration in MS disease.

A new focal model resembling features of cortical pathology of the progressive forms of multiple sclerosis: Influence of innate immunity

Multiple sclerosis (MS) is an inflammatory and demyelinating disease of unknown aetiology that causes neurological disabilities in young adults. MS displays different clinical patterns, including recurrent episodes with remission periods ("relapsing-remitting MS" (RRMS)), which can progress over several years to a secondary progressive form (SPMS). However, 10% of patients display persistent progression at the onset of disease ("primary progressive MS" (PPMS)). Currently, no specific therapeutic agents are available for the progressive forms, mainly because the underlying pathogenic mechanisms are not clear and because no animal models have been specifically developed for these forms. The development of MS animal models is required to clarify the pathological mechanisms and to test novel therapeutic agents. In the present work, we overexpressed interleukin 1 beta (IL-1β) in the cortex to develop an animal model reflecting the main pathological hallmarks of MS. The treated animals presented with neuroinflammation, demyelination, glial activation, and neurodegeneration along with cognitive symptoms and MRI images consistent with MS pathology. We also demonstrated the presence of meningeal inflammation close to cortical lesions, with characteristics similar to those described in MS patients. Systemic pro-inflammatory stimulation caused a flare-up of the cortical lesions and behavioural symptoms, including impairment of working memory and the appearance of anxiety-like symptoms. Our work demonstrated induced cortical lesions, reflecting the main histopathological hallmarks and cognitive impairments characterizing the cortical pathology described in MS patients with progressive forms of the disease.

Remotely Supervised Transcranial Direct Current Stimulation Increases the Benefit of At-Home Cognitive Training in Multiple Sclerosis

OBJECTIVE

To explore the efficacy of remotely-supervised transcranial direct current stimulation (RS-tDCS) paired with cognitive training (CT) exercise in participants with multiple sclerosis (MS).

METHODS

In a feasibility study of RS-tDCS in MS, participants completed ten sessions of tDCS paired with CT (1.5 mA × 20 min, dorsolateral prefrontal cortex montage). RS-tDCS participants were compared to a control group of adults with MS who underwent ten 20-min CT sessions through the same remotely supervised procedures. Cognitive outcomes were tested by composite scores measuring change in performance on standard tests (Brief International Cognitive Assessment in MS or BICAMS), basic attention (ANT-I Orienting and Attention Networks, Cogstate Detection), complex attention (ANT-I Executive Network, Cogstate Identification and One-Back), and intra-individual response variability (ANT-I and Cogstate identification; sensitive markers of disease status).

RESULTS

After ten sessions, the tDCS group (n = 25) compared to the CT only group (n = 20) had significantly greater improvement in complex attention (p = 0.01) and response variability (p = 0.01) composites. The groups did not differ in measures of basic attention (p = 0.95) or standard cognitive measures (p = 0.99).

CONCLUSIONS

These initial findings indicate benefit for RS-tDCS paired with CT in MS. Exploratory analyses indicate that the earliest tDCS cognitive benefit is seen in complex attention and response variability. Telerehabilitation using RS-tDCS combined with CT may lead to improved outcomes in MS.