The A4 study is a clinical trial for older individuals who have evidence of amyloid plaque build-up in their brains who may be at risk for memory loss and cognitive decline due to Alzheimer's disease. The A4 study will test an anti-amyloid investigational drug in older individuals who do not yet show symptoms of Alzheimer's disease cognitive impairment or dementia with the aim of slowing memory and cognitive decline. The A4 study will also test whether anti-amyloid treatment can delay the progression of AD related brain injury on imaging and other biomarkers.