Jacksonville, Florida


Day.Gregory@mayo.edu Clinical Profile


Gregory (Gregg) S. Day, M.D., is a neurologist, dementia specialist and clinical researcher. Dr. Day is focused on improving the clinical diagnoses and characterization of common and uncommon causes of dementia, including neurodegenerative and autoimmune-mediated brain diseases. His research integrates clinical and paraclinical measures such as structural and functional neuroimaging and biofluid biomarkers. Dr. Day employs these methods to determine the causes and contributing factors of dementia, improve clinical diagnosis, and optimize treatment with the goal of improving long-term patient outcomes.

Focus areas

  • Dementia. Dr. Day aims to determine the causes of dementia with a special focus on rapidly progressive forms of dementia. This work includes studies designed to identify and apply protein measures in blood and cerebrospinal fluid to recognize specific causes of dementia during the life span.
  • Creutzfeldt-Jakob disease. This area of research seeks to advance diagnosis and care for patients with this disease.
  • Treatment-responsive dementia. The goal of this research is to improve the recognition of patients with dementia that is potentially responsive to treatment early in the symptomatic course of the disease.
  • Advancing treatment. Dr. Day evaluates the effectiveness of dementia medications in clinical trials.
  • Autoimmune encephalitis. Dr. Day focuses on designing and leading clinical trials for patients with this condition.

Significance to patient care

Dr. Day's research improves patient care by developing diagnostic approaches, tools and tests that can be used to recognize patients with specific causes of dementia early in the symptomatic course. Early recognition and accurate characterization of dementia are critical to ensure that patients get access to the right treatments, when available, at a time when they're most likely to be effective. Early recognition and accurate diagnosis also ensure that patients and families have access to accurate disease-specific information and support throughout the course of the illness.

Professional highlights

  • Chair, Geriatric Neurology Quality Measures Work Group, American Academy of Neurology, 2021-present.
  • Co-principal investigator, The ExTINGUISH Trial of Inebilizumab in NMDAR Encephalitis, National Institute of Neurological Disorders and Stroke, 2021-present.
  • Director, Division of Behavioral Neurology, Department of Neurology, Mayo Clinic, 2021-present.
  • Vice chair of research, Department of Neurology, Mayo Clinic, 2021-present.


Primary Appointment

  1. Department of Neurology

Academic Rank

  1. Assistant Professor of Neurology


  1. Master of Science - Clinical Investigation Washington University in St. Louis
  2. Graduate Certificate - Clinical Investigation Washington University in St. Louis
  3. Fellowship - Memory and Aging Washington University in St. Louis
  4. Residency - Adult Neurology University of Toronto
  5. MD Queen's University
  6. MSc - Neuroscience Studies Queen's University
  7. BS - Life Sciences (Research Stream) Queen's University

Clinical Studies

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