Motor unit number estimation (MUNE) is a unique neurophysiological technique that estimates the number of motor units (MUs) and provides information on rates of motor unit decline and collateral reinnervation. This technique calculates the number of MU by dividing the averaged amplitude of several single motor unit potential (SMUP) from compound muscle action potential recorded with supramaximal stimulation. It is well known that can be a physiological biomarker and reflects their pathology in motor neuron disease. Meanwhile, F-wave is a backfiring motor response generated by electrical stimulation via spinal anterior horn cell, composed of several motor units in the motor neuron pool. The waveforms of F-wave become different because the firing probability of MU changes generally at every timing. Therefore, the repeater F-waves (RF), in which the same waveform is repeatedly recorded, are known to generate from the same MU in motor neuron disease, in which the number of motor units decreased in their pathology. MUNE is based on the automated analysis of F-wave (F-MUNE) that interprets RF as SMUP. We developed an automated F-MUNE analysis program and evaluated its utility. We compared its results between the patients with amyotrophic lateral sclerosis (ALS) and healthy controls (CNT). In addition, we determined the correlation between the results of F-MUNE and MUNE by multiple point stimulation (MPS-MUNE). F-MUNE in ALS was lower than that in CNT, and the results of MPS-MUNE were similar. In addition, there was a positive correlation between the results of the two MUNEs. F-MUNE give a quantitative measure of the number of MUs in ALS, hence this technique can refract the motor unit pathology in motor neuron disease.

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Jewett et al. (1970) were the first to record auditory brainstem responses (ABR) over the human scalp. Halliday et al. (1972) were the first to report the usefulness of visual evoked potentials (VEPs) from pattern-reversal stimulation in the evaluation of optic neuritis in multiple sclerosis (MS). This paper outlines the contribution of these two techniques to clinical neurophysiology. With the advent of ABR, the auditory pathway of the brainstem can now be objectively assessed and has become the basic test for determining hearing ability and assessing brainstem function. ABR has also contributed significantly to the development of short latency somatosensory evoked potentials (SEPs), which are far-field potentials. This made it possible to record peripheral nerve and spinal cord potentials from over the human scalp. While flash VEPs were difficult to apply clinically because of waveform variability in the same individual and between individuals, the pattern VEPs of Halliday et al. were recorded stably and became a diagnostic criterion for MS. Subsequently, from the perspective of parallel visual information processing, the authors developed a multimodality VEP. This enabled the pathological evaluation of neuropsychiatric disorders. As those involved in clinical neurophysiology, we should not forget the original ideas of our predecessors and hope to develop techniques that surpass them.

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The history of somatosensory evoked potential (SEP) research is reviewed, and future challenges and prospects are discussed. The world’s first report of SEPs in patients with myoclonus epilepsy was a giant SEP response obtained by EEG superimposition after sensory stimulation. In the 1970s and 1980s, the SEP components were clinically applied to the somatosensory conduction pathways to the cerebrum, and the activity at various levels of these pathways was of great interest. There was a great controversy over whether the early cortical responses in humans originated from area 3b or areas 1 and 4, but magnetic field measurements confirmed the tangential current source, indicating that area 3b origin is correct and that the area 1 response is superimposed after a delay of about 2 ms. The study of 600 Hz high-frequency signals superimposed on early cortical responses has now become a new field of clinical application and research, and future research is expected to develop on the spatiotemporal characteristics of activity in the 3b and 1 cortices and its relation to beta oscillations in sensorimotor cortex.

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The discovery of brain potential that preceded voluntary movement by Drs. Kohhuber and Deecke in 1964 with the identification of each component of the MRCP (movement-related-cortical potential) by Dr. Shibasaki in 1980 opened the door of motor control research. Although the exact origin of MRCP in the motor cortex has long been unknown, investigating MRCP as the epilepsy presurgical evaluation with electrocorticography confirmed the role of MRCP in the primary and supplementary motor area (Ikeda et al., 1992 Brain, Ohara et al., 2000 Brain), expanding the clinical applications. Additionally, the concept of event-related synchronization/de-synchronization (ERS/ERD) with a time-frequency analysis established by Pfurtscheller was highly appreciated. Along this line, multi-spectrum intrinsic brain activities with a different spectral range, very slow potentials (MRCP) to high-frequency activity (ERS and ERD), allow us to advance the accuracy of systematic brain mapping (Neshige et al., Clin Neurophysiol 2018) and developed the scoring system to identify the primary and negative motor cortices (Neshige et al., Epilepsia 2019). Multi-spectrum intrinsic brain activity is reasonable, further implacable for the future design of motor physiology investigation. This study has been presented to the Annual Meeting of the Japanese Clinical Neurophysiology Society, and an abstract has appeared in its proceedings.

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[in Japanese]

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[in Japanese]

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[in Japanese]

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