Deficits in Early Sensory and Cognitive Processing Are Related to Phase and Nonphase EEG Activity in Multiple Sclerosis Patients.

Esteban Sarrias-Arrabal,Guillermo Izquierdo,Manuel Vázquez-Marrufo,Sara Eichau,Elvira Domínguez,Alejandro Galvao-Carmona

doi:10.3390/brainsci11050629

Abstract

Currently, there is scarce knowledge about the relation between spectral bands modulations and the basis of cognitive impairment in multiple sclerosis (MS). In this sense, analyzing the evoked or phase activity can confirm results from traditional event-related potential (ERP) studies. However, studying the induced or nonphase activity may be necessary to elucidate hidden compensatory or affected cognitive mechanisms. In this study, 30 remitting-relapsing multiple sclerosis patients and 30 healthy controls (HCs) matched in sociodemographic variables performed a visual oddball task. The main goal was to analyze phase and nonphase alpha and gamma bands by applying temporal spectral evolution (TSE) and its potential relation with cognitive impairment in these patients. The behavioural results showed slower reaction time and poorer accuracy in MS patients compared to controls. In contrast, the time-frequency analysis of electroencephalography (EEG) revealed a delay in latency and lower amplitude in MS patients in evoked and induced alpha compared to controls. With respect to the gamma band, there were no differences between the groups. In summary, MS patients showed deficits in early sensorial (evoked alpha activity) and cognitive processing (induced alpha activity in longer latencies), whereas the induced gamma band supported the hypothesis of its role in translation of attentional focus (induced activity) and did not show strong activity in this paradigm (visual oddball).

Highlights

Multiple sclerosis (MS) is a neurodegenerative disease of unknown etiology, in which the main neurological damage is demyelination and inflammation of the central nervous system (CNS) [1]
The data showed no differences in latency or amplitude between groups (Figure 4). Based on these results, we suggest that the MS patients did not manifest alterations in the mechanisms indexed by the early gamma-evoked response as previously described [20]
There were differences in amplitude between groups for the longer latencies in the induced activity but not for the evoked modulation. These results indicate that induced modulation represents a linked mechanism to the evoked response, representing a reduction in neural noise that competes with the sensory processing of the stimuli represented by the evoked response but is related to other cognitive processes that operate later in information processing

Summary

Introduction

Multiple sclerosis (MS) is a neurodegenerative disease of unknown etiology, in which the main neurological damage is demyelination and inflammation of the central nervous system (CNS) [1]. MS shows diverse cognitive deficits in 40–70% of cases [1], and different neuropsychological profiles have been found by clinical assessments. Diverse studies have defined that attention, processing speed and memory are the cognitive domains most frequently affected [3,4]. The oddball task can be a useful tool because changes in ERPs correlate with changes in scores of neuropsychological tests [9,10] and magnetic resonance imaging (MRI) parameters [6,11]. Even ERPs obtained while performing visual oddball tasks predict cognitive functioning and processing speed in patients with MS [12]

Objectives

Methods

Findings

Discussion

Conclusion