Cognitively normal individuals, patients with Mild Cognitive Impairment (MCI) or Alzheimer's Disease (AD) will undergo clinical screening, neuropsychological tests, blood and urine analyses, quantitative magnetic resonance imaging (MRI) and proton (1H ) and carbon 13 (13C) magnetic resonance spectroscopy (MRS). Each individual will receive minocycline oral administration for 4 weeks initially, after which MRI, MRS and neuropsychological results will be recorded. If no adverse side effects occur, subjects will continue minocycline administration for an additional 5 months.