Transcranial Magnetic Stimulation in Alzheimer’s Disease: A Review of Investigational and Therapeutic Findings

Alzheimer’s disease pathophysiology still remains unclear and current pharmacological strategies have limited effectiveness, so that the search for alternative and/or complementary therapeutic strategies is a compelling need, as well as a detailed characterization of the disease progression and its neurophysiological correlates. Transcranial Magnetic Stimulation (TMS),has been employed by a number of studies to physiologically characterize AD, investigating cortical reactivity, plasticity and functional connectivity. A few studies also investigated the therapeutic role of repetitive TMS to enhance cognitive functions in AD. Herein we review a total of thirty-two studies evaluating both investigational and therapeutic role of TMS. Although promising, therapeutic results are still very preliminary and need to be taken with caution, while insights have been provided by most investigational studies. *Corresponding author: Stefano Pallanti, M.D., Ph.D., 3 Largo Brambilla, 50134 Firenze, Italy, Tel: 055 794 9707; Fax: 055 581051; E-mail: [email protected] Received February 12, 2015; Accepted March 31, 2015; Published April 07, 2015 Citation: Pallanti S, Marras A (2015) Transcranial Magnetic Stimulation in Alzheimer’s Disease: A Review of Investigational and Therapeutic Findings. J Alzheimers Dis Parkinsonism 5: 187. doi: 10.4172/2161-0460.1000187 Copyright: © 2015 Pallanti S, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. several neurodegenerative and neuropsychiatric disorders (Parkinson’s disease, tremor, obsessive-compulsive disorder, major depression) [810]. Recently, its use in other neurodegenerative disorders, such as AD, is being considered. Compared to TMS, DBS represent an invasive neuromodulation technique, which requires careful patient selection and follow-up. Therefore, its use is restricted to a limited number of suitable candidates and the literature regarding its employ in AD is still preliminary. Herein, we provide a brief review of the most consistent neurophysiologic findings and preliminary therapeutic results obtained with TMS in AD. TMS as an investigational tool In the last two decades, TMS has been employed to investigate cortical reactivity, plasticity and functional connectivity: we reviewed a total of 25 studies [11-35], of which 22 focused on several cortical reactivity measures [11-22,24,25,27,28,30-34] and the remaining 3 focused on cortical plasticity and connectivity measures [23,26,28] (Table 1). Cortical reactivity measures: The most consistent finding from reviewed studiesis a decreased resting motor threshold (RMT) in AD patients compared to controls, found in 15 of 24 studies assessing this measure [12-20,23,24,27,29,31,32,34]: RMT is the basic unit of transcranial magnetic stimulation dosing and it is thought to reflect membrane excitability of corticospinal neurons and interneurons projecting onto these neurons in the motor cortex [4]. Only one study [11] found increased RMT in AD patients, and the remaining 8 [15,21,25,26,28,30,33,35] found no significant differences: the overall results of a decreased RMT in AD seem to support the notion of a motor cortex hyper excitability in the disease. Citation: Pallanti S, Marras A (2015) Transcranial Magnetic Stimulation in Alzheimer’s Disease: A Review of Investigational and Therapeutic Findings. J Alzheimers Dis Parkinsonism 5: 187. doi: 10.4172/2161-0460.1000187