Foundations Of Cognitive Science

Alzheimer's Disease

Alzheimer's Disease (AD), a term coined by Alois Alzheimer in 1907, is a relentlessly progressive disease characterized by cognitive decline, behavioural disturbances, and changes in personality. Current estimates of prevalence of AD in Canada suggest that 5.1% of all Canadians 65 and over meet the criteria for the clinical diagnosis of AD. AD prevalence is slightly higher in women than in men, perhaps because of the longer life expectancy of women although other factors have not been ruled out. The prevalence of dementia is strongly associated with age, affecting 1% of the Canadian population aged 65 to 74, 6.9% of individuals 75-84 and 26% of individuals 85 years and older (Canadian Study of Health and Aging, 1994).

The diagnostic criteria for dementia of the Alzheimer's Type (DAT) are as follows:

  • (A) The development of multiple cognitive deficits manifested by both:
    1. Memory impairment (impaired ability to learn new information or to recall previously learned information)
    2. One or more of the following cognitive disturbances:
      • aphasia (language disturbance)
      • apraxia (impaired ability to carry out motor activities despite intact motor function)
      • agnosia (failure to recognize or identify objects despite intact sensory function)
      • disturbances in executive functioning (i.e., planning, organizing, sequencing, abstracting)
  • (B) The cognitive deficits in Criteria A1 and A2 each cause significant impairment in social and occupational functioning and represent a significant decline from a previous level of functioning.
  • (C) The course is characterized by gradual onset and continuing cognitive decline
  • (D) The cognitive deficits in Criteria A1 and A2 are not due to any of the following:
    1. other central nervous system conditions that cause progressive deficits in memory and cognition (e.g., cerebrovascular disease, Parkinson's Disease, Huntington's Disease, subdural hematoma, normal pressure hydrocephalus, brain tumor).
    2. systemic conditions that are known to cause a dementia (e.g., hypothyroidism, vitamin B12 or folic acid deficiency, hypercalcemia, neurosyphilis, HIV infection)
    3. substance-induced conditions
  • (E) The deficits do not occur exclusively during the course of a delirium
  • (F) The disturbance is not better accounted for by another Axis 1 disorder (e.g., Major Depressive Disorder, Schizophrenia)

The diagnosis of AD is based on exclusionary criteria (i.e., the absence of an identifiable cause) with diagnosis confirmed at autopsy. Treatment strategies to date have been largely ineffective, with experimental treatments mainly directed toward overcoming the cholinergic deficit.


  1. American Psychiatric Association (1994). Diagnostic and statistical manual of mental disorders (4th ed.). Washington, DC: Author.
  2. Canadian study of health and aging: Study methods and prevalence of dementia. (1994). Canadian Medical Association Journal, 150(6).
  3. Whitehouse, P.J. (1993) Dementia. Philadelphia: F.A. Davis.

(Revised November 2009)