Disinhibition of sensory cortex in patients with amyotrophic lateral sclerosis

In patients with amyotrophic lateral sclerosis (ALS) a motor cortical hyperexcitability has been reported in transcranial magnetic stimulation studies, but little is known about the neuronal excitability in other cortical areas. The aim of the present study was the functional evaluation of the sensory cortex in subjects with ALS by assessing the high-frequency somatosensory evoked potentials (HF-SEP). No significant HF-SEP abnormalities were observed in ALS patients with disease duration of < 2 years, while the patients with a disease duration of > 2 years we found a large amplitude reduction of post-synaptic HF-SEP burst. Since post-synaptic burst of HF-SEP is thought to reflect the activity of cortical inhibitory interneurons, our findings provide further evidence that disinhibition is a primary characteristic of ALS that also involves the somatosensory cortex.