title: Motor cortex excitability in Alzheimer's disease: a transcranial magnetic stimulation study.
abstract: Motor deficits affect patients with Alzheimer's disease only at later stages. Recent studies demonstrate that the primary motor cortex is affected by neuronal degeneration accompanied by the formation of amyloid plaques and neurofibrillary tangles. It is conceivable that neuronal loss is compensated by reorganization of the neural circuitries occurring along the natural course of the disease, thereby maintaining motor performances in daily living. Cortical motor output to upper limbs was tested via motor-evoked potentials from forearm and hand muscles elicited by transcranial magnetic stimulation of motor cortex in 16 patients with mild Alzheimer's disease without motor deficits. Motor cortex excitability was increased, and the center of gravity of motor cortical output, as represented by excitable scalp sites, showed a frontal and medial shift, without correlated changes in the site of maximal excitability (hot-spot). This may indicate functional reorganization, possibly after the neuronal loss in motor areas. Hyperexcitability might be caused by a dysregulation of the intracortical GABAergic inhibitory circuitries and selective alteration of glutamatergic neurotransmission. Such findings suggest that motor cortex hyperexcitability and reorganization allows prolonged preservation of motor function during the clinical course of Alzheimer's disease.
authors.affiliation: Department of Neurology, University Campus Biomedico, Isola Tiberina, Rome, Italy.
authors.forename: Florinda
authors.initials: F
authors.lastname: Ferreri
authors.forename: Flavia
authors.initials: F
authors.lastname: Pauri
authors.forename: Patrizio
authors.initials: P
authors.lastname: Pasqualetti
authors.forename: Rita
authors.initials: R
authors.lastname: Fini
authors.forename: Gloria
authors.initials: G
authors.lastname: Dal Forno
authors.forename: Paolo Maria
authors.initials: PM
authors.lastname: Rossini
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000544:Alzheimer Disease / Q000503:physiopathology*; D004558:Electric Stimulation; D019054:Evoked Potentials, Motor; D005260:Female; D005542:Forearm; D006225:Hand; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000503:physiopathology*; D050781:Transcranial Magnetic Stimulation