Motor cortex inhibition is not impaired in patients with Alzheimer's disease: evidence from paired transcranial magnetic stimulation.

Motor cortex excitability was studied by transcranial magnetic stimulation (TMS) in 17 patients with Alzheimer's disease (AD). Resting and active thresholds for TMS were significantly reduced in AD patients compared to young and aged healthy subjects. The maximum amplitude of the motor response evoked by TMS was also significantly increased in AD patients. We have tested if these changes are related to a modification of the short-lasting intracortical inhibition of the motor cortex by paired conditioning-test TMS. We found no significant differences between AD patients and aged healthy subjects even if there is a slight but significant difference between aged and young normal subjects. We conclude that the modification of excitability of the motor cortex does not result from an impaired intracortical inhibition.