Role of the Upper Motor Neuron in the Generation of Fasciculations in Early Disease Stages of Amyotrophic Lateral Sclerosis

BACKGROUND AND OBJECTIVES: The origin of fasciculation potentials (FPs) in the early stages of amyotrophic lateral sclerosis (ALS) remains a subject of debate. We investigated the role of the motor cortex in FP generation by comparing resting FP frequency in the first dorsal interosseous (FDI) muscle before and after motor cortex inhibition induced by continuous theta-burst stimulation (cTBS). METHODS: < 0.05. RESULTS: = 0.14). Patients with ALS with a normal FDI EMG demonstrated an even greater reduction in FP frequency (54.5%). FP amplitudes remained stable across both groups after cTBS. DISCUSSION: Our findings indicate that in early ALS, LMN excitability is significantly modulated by descending corticospinal input. The reduction in FP frequency after cortical inhibition suggests that FPs in early ALS are driven by a combination of both UMN and LMN hyperexcitability, distinguishing them from fasciculations in other neurogenic disorders.