title: Altered Cortical Synaptic Plasticity in Response to 5-Hz Repetitive Transcranial Magnetic Stimulation as a New Electrophysiological Finding in Amnestic Mild Cognitive Impairment Converting to Alzheimer's Disease: Results from a 4-year Prospective Cohort Study.
abstract: BACKGROUND
  To investigate cortical excitability and synaptic plasticity in amnestic mild cognitive impairment (aMCI) using 5 Hz repetitive transcranial magnetic stimulation (5 Hz-rTMS) and to assess whether specific TMS parameters predict conversion time to Alzheimer's disease (AD).
  
  
  METHODS
  Forty aMCI patients (single- and multi-domain) and 20 healthy controls underwent, at baseline, a neuropsychological examination and 5 Hz-rTMS delivered in trains of 10 stimuli and 120% of resting motor threshold (rMT) intensity over the dominant motor area. The rMT and the ratio between amplitude of the 1st and the 10th motor-evoked potential elicited by the train (X/I-MEP ratio) were calculated as measures of cortical excitability and synaptic plasticity, respectively. Patients were followed up annually over a period of 48 months. Analysis of variance for repeated measures was used to compare TMS parameters in patients with those in controls. Spearman's correlation was performed by considering demographic variables, aMCI subtype, neuropsychological test scores, TMS parameters, and conversion time.
  
  
  RESULTS
  Thirty-five aMCI subjects completed the study; 60% of these converted to AD. The baseline rMT and X/I-MEP ratio were significantly lower in patients than in controls (p = 0.04 and p = 0.01). Spearman's analysis showed that conversion time correlated with the rMT (0.40) and X/I-MEP ratio (0.51).
  
  
  CONCLUSIONS
  aMCI patients displayed cortical hyperexcitability and altered synaptic plasticity to 5 Hz-rTMS when compared with healthy subjects. The extent of these changes correlated with conversion time. These alterations, which have previously been observed in AD, are thus present in the early stages of disease and may be considered as potential neurophysiological markers of conversion from aMCI to AD.
authors.affiliation: Department of Neurology and Psychiatry, Sapienza University of Rome , Rome , Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Trebbastoni
authors.affiliation: Department of Neurology and Psychiatry, Sapienza University of Rome, Rome, Italy; Neuroelectrical Imaging and Brain Computer Interface Laboratory, Fondazione Santa Lucia - Istituto di Ricovero e Cura a Carattere Scientifico (IRCCS), Rome, Italy.
authors.forename: Floriana
authors.initials: F
authors.lastname: Pichiorri
authors.affiliation: Department of Neurology and Psychiatry, Sapienza University of Rome , Rome , Italy.
authors.forename: Fabrizia
authors.initials: F
authors.lastname: D'Antonio
authors.affiliation: Department of Neurology and Psychiatry, Sapienza University of Rome , Rome , Italy.
authors.forename: Alessandra
authors.initials: A
authors.lastname: Campanelli
authors.affiliation: Department of Neurology and Psychiatry, Sapienza University of Rome , Rome , Italy.
authors.forename: Emanuela
authors.initials: E
authors.lastname: Onesti
authors.affiliation: Department of Neurology and Psychiatry, Sapienza University of Rome , Rome , Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Ceccanti
authors.affiliation: Department of Neurology and Psychiatry, Sapienza University of Rome , Rome , Italy.
authors.forename: Carlo
authors.initials: C
authors.lastname: de Lena
authors.affiliation: Department of Neurology and Psychiatry, Sapienza University of Rome , Rome , Italy.
authors.forename: Maurizio
authors.initials: M
authors.lastname: Inghilleri
keywords: Alzheimer’s disease; N-methyl-d-aspartate acid receptor; cortical excitability; mild cognitive impairment; synaptic plasticity; transcranial magnetic stimulation