His main findings include the discovery of the ischemic penumbra in humans and the crucial role of hemodynamic impairment in carotid-territory TIAs, as well as crossed cerebellar diaschisis and thalamo-cortical diaschisis.

He has used functional and structural brain imaging to examine the mechanisms underlying cerebral amyloid angiopathy and neurodegenerative illnesses such as Alzheimer's, Parkinson's, and Progressive Supranuclear Palsy.