title: The relationship between motor cortex excitability and severity of Alzheimer's disease: a transcranial magnetic stimulation study.
abstract: BACKGROUND
  In Alzheimer's disease (AD), transcranial magnetic stimulation (TMS) studies have been limited to test motor cortical excitability. The aim of this study was to investigate the inhibitory circuits of the motor cortex and to relate these to measures of cognitive function in AD patients. Results were compared with those of a control group of healthy subjects matched for age, sex and education.
  
  
  METHODS
  Forty-five AD patients and 37 healthy volunteers were included in the study. Each participant received a neurological evaluation, Mini-Mental State Examination (MMSE), and Clinical Dementia Rating (CDR). Neurophysiological evaluations included resting and active motor threshold (rMT and aMT), motor evoked potential (MEP), cortical silent period (CSP), and transcallosal inhibition (TI).
  
  
  RESULTS
  AD patients showed significantly reduced rMT, aMT and shorter MEP onset latency; in addition there was a prolongation of both CSP and TI. There was a significant positive correlation between the MMSE and CDR, on the one hand, and aMT and rMT, on the other hand, whereas the correlation was negative with CSP and TI durations.
  
  
  CONCLUSIONS
  AD is associated with hyperexcitability of the motor cortex, which supports the hypothesis that changes in GABAb and glutamate function are important factors in cognitive impairment.
authors.affiliation: Department of Neurology and Neuropsychiatry, Assiut University Hospital, Assiut, Egypt. Emankhedr99@yahoo.com
authors.forename: E M
authors.initials: EM
authors.lastname: Khedr
authors.forename: M A
authors.initials: MA
authors.lastname: Ahmed
authors.forename: E S
authors.initials: ES
authors.lastname: Darwish
authors.forename: A M
authors.initials: AM
authors.lastname: Ali
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000544:Alzheimer Disease / Q000503:physiopathology*; D003072:Cognition Disorders / Q000503:physiopathology; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000503:physiopathology*; D012720:Severity of Illness Index; D050781:Transcranial Magnetic Stimulation