Motor cortex excitability in Alzheimer's disease: a transcranial magnetic stimulation follow-up study

Transient cognitive and behavioral stabilization of patients with Alzheimer's disease (AD) is the main goal of acetylcholinesterase inhibitor (AChEI) therapy. Response to treatment is variable and it is usually assessed clinically via neuropsychological scales. Functional neuroimaging could ideally permit the objective evaluation of the topographic correlates of therapy on brain functioning, but is expensive and little available on a large scale. On the other hand, neurophysiological methods such as transcranial magnetic stimulation (TMS) could offer an alternative, low-cost and risk free tool of assessing response to treatment in AD. Previous TMS studies have demonstrated hyperexcitability and asymptomatic motor cortex reorganization in the early stages of AD in patients with normal motor function. The aim of this study was to compare motor cortex functionality in 10 AD patients before and after long-term AchEIs therapy in order to monitor potential drug-related changes in cortical excitability and organization. Examined parameters of motor cortex physiology were found to be unchanged in patients with stabilized cognitive performance during the therapy. TMS, along with clinical, neuropsychological, and neuroimaging data, could be an inexpensive measure of biological progression in AD and it might supplement traditional methods to assess the effects of therapy.

Research highlights
► First study to compare TMS Mapping of M1 in AD before and after long-term AchEIs.
► M1 functionality was stable in patients with stabilized cognitive performance.
► Findings support hypothesis that cortical excitability parallels cognitive status.
► TMS could emerge as an inexpensive measure of biological progression in AD.
► TMS might supplement traditional methods to assess the effects of therapy.