Magnetic Source Imaging of Cortical Dysfunction in Amyotrophic Lateral Sclerosis

Electrophysiological correlates of neurodegeneration in motor and non-motor brain regions in amyotrophic lateral sclerosis-implications for brain-computer interfacing

OBJECTIVE

For patients with amyotrophic lateral sclerosis (ALS) who are suffering from severe communication or motor problems, brain-computer interfaces (BCIs) can improve the quality of life and patient autonomy. However, current BCI systems are not as widely used as their potential and patient demand would let assume. This underutilization is a result of technological as well as user-based limitations but also of the comparatively poor performance of currently existing BCIs in patients with late-stage ALS, particularly in the locked-in state.

APPROACH

Here we review a broad range of electrophysiological studies in ALS patients with the aim to identify electrophysiological correlates of ALS-related neurodegeneration in motor and non-motor brain regions in to better understand potential neurophysiological limitations of current BCI systems for ALS patients. To this end we analyze studies in ALS patients that investigated basic sensory evoked potentials, resting-state and task-based paradigms using electroencephalography or electrocorticography for basic research purposes as well as for brain-computer interfacing. Main results and significance. Our review underscores that, similarly to mounting evidence from neuroimaging and neuropathology, electrophysiological measures too indicate neurodegeneration in non-motor areas in ALS. Furthermore, we identify an unexpected gap of basic and advanced electrophysiological studies in late-stage ALS patients, particularly in the locked-in state. We propose a research strategy on how to fill this gap in order to improve the design and performance of future BCI systems for this patient group.

Amyotrophic lateral sclerosis: Is the spinal fluid pathway involved in seeding and spread?

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder manifested primarily by loss of upper and lower motor neurons. Current explanations for disease progression invoke regional spread attributed to the transfer of pathogenic factors among physically contiguous neurons. However, this explanation incompletely explains certain clinical and in vitro data. Considering this, we propose that the cerebrospinal fluid (CSF) pathway is likely to be a key vector for seeding local and distal disease. Subsequent disease progression would be expected to occur independently via either axonal or CSF transmission. If one accepts the hypothesis that the CSF pathway is involved in ALS progression, it follows that the choroid plexus (CP) might well be a driver of the disease process. In support of this, we briefly review the anatomical and physiological features of the CSF pathway and the choroid plexus responsible for secreting CSF. In addition, we draw attention to the interface of the CP and CSF with the immune system. We then summarize both clinical and cell culture research that supports a key role of the CSF in the establishment and inter-neuronal spread of ALS, and which suggest directions for translational research.

The application of biomarkers in clinical trials for motor neuron disease

The interest and research into disease-related biomarkers has greatly accelerated over the last 10 years. The potential clinical benefits for disease-specific biomarkers include a more rapid and accurate disease diagnosis, and potential reduction in size and duration of clinical drug trials, which would speed up drug development. The application of biomarkers into the clinical arena of motor neuron disease should both determine if a drug hits its proposed target and whether the drug alters the course of disease. This article will highlight the progress made in discovering suitable biomarker candidates from a variety of sources, including imaging, neurophysiology and proteomics. For biomarkers to have clinical utility, specific criteria must be satisfied. While there has been tremendous effort to discover biomarkers, very few have been translated to the clinic. The bottlenecks in the biomarker pipeline will be highlighted as well as lessons that can be learned from other disciplines, such as oncology.