In Vivo Imaging of Amyloid Deposition in Alzheimer Disease Using the Radioligand ¹⁸F-AV-45 (Flobetapir F 18)

TLDR

The decrease in cortical excitability after low‑frequency TMS may resemble long‑term depression (LTD) mechanisms. The study investigated the effects of low‑frequency transcranial magnetic stimulation on motor cortex excitability in humans. The authors applied low‑frequency TMS to the motor cortex to assess changes in excitability. Low‑frequency TMS at 0.9 Hz reduced motor evoked potential amplitude by 19.5 % and lowered cortical excitability for at least 15 min, whereas 0.1 Hz stimulation had no effect, suggesting potential therapeutic use but also highlighting the need for monitoring due to possible spread of excitation.

Abstract

We studied the effects of low-frequency transcranial magnetic stimulation (TMS) on motor cortex excitability in humans. TMS at 0.1 Hz for 1 hour did not change cortical excitability. Stimulation at 0.9 Hz for 15 minutes (810 pulses), similar to the parameters used to induce long-term depression (LTD) in cortical slice preparations and in vivo animal studies, led to a mean decrease in motor evoked potential (MEP) amplitude of 19.5%. The decrease in cortical excitability lasted for at least 15 minutes after the end of the 0.9 Hz stimulation. The mechanism underlying this decrease in excitability may be similar to LTD. TMS-induced reduction of cortical excitability has potential clinical applications in diseases such as epilepsy and myoclonus. Spread of excitation, which may be a warning sign for seizures, occurred in one subject and was not accompanied by increased MEP amplitude, suggesting that spread of excitation and amplitude changes are different phenomena and also indicating the need for adequate monitoring even with stimulations at low frequencies.