Resting-State EEG Oscillations in Amyotrophic Lateral Sclerosis (ALS): Toward Mechanistic Insights and Clinical Markers

Abstract

Introduction: Amyotrophic lateral sclerosis (ALS) is a complex, progressive neurodegenerative disorder characterized by the degeneration of motor neurons in the brain, brainstem, and spinal cord. Several neuroimaging techniques can help reveal the pathophysiology of ALS. One of these is the electroencephalogram (EEG), a noninvasive and relatively inexpensive tool for examining electrical activity of the brain with excellent temporal precision. Methods: This mechanistic review examines the pattern of resting-state EEG activity. With a focus on publications published between January 1995 and October 2024, we carried out a comprehensive search in October 2024 across a number of databases, including PubMed/Medline, Research Gate, Google Scholar, and Cochrane. Results: The literature search yielded 17 studies included in this review. The studies varied significantly in their methodology and patient characteristics. Despite this, a common biomarker typical of ALS was found-reduced alpha power. Regarding other oscillations, the findings are less consistent and sometimes contradictory. As this is a mechanistic review, three possible explanations for this biomarker are provided. The main and most important one is increased cortical excitability. In addition, due to the limitations of the studies, recommendations for future research on this topic are outlined to enable a further and better understanding of EEG patterns in ALS. Conclusions: Most studies included in this review showed alpha power deficits in ALS patients, reflecting pathological hyperexcitability of the cerebral cortex. Future studies should address the methodological limitations identified in this review, including small sample sizes, inconsistent frequency-band definitions, and insufficient functional outcome measures, to solidify and extend current findings.

Keywords: ALS; EEG; QEEG; amyotrophic lateral sclerosis; electroencephalogram; electroencephalography; electrophysiology; neural correlates; neuroimaging; neurophysiology; oscillations.

Figure 1

Flow chart depicting the different phases of the systematic review. This flow chart illustrates the phases of the systematic review, including the initial database search yielding 1320 studies, screening, exclusion, and the final inclusion of 17 studies. It highlights the number of records excluded at each stage and the final studies included for detailed analysis.

Figure 2

Pathophysiological mechanisms of ALS based on consistent EEG findings. This figure depicts the key pathophysiological mechanisms underlying ALS as revealed by consistent findings from resting-state EEG studies. It provides a conceptual framework linking EEG biomarkers to ALS pathophysiology.