The concept of subcortical dementia.
The authors review the concept of subcortical dementia, specifically the dementia associated with Huntington's disease, Parkinson's disease, and progressive supranuclear palsy, all subcortical processes that involve deterioration of mental abilities. Subcortical dementia affords a unique opportunity to study the progressive memory loss associated with dementia because, in contrast to cortical dementias such as Alzheimer's disease, this relatively circumscribed syndrome does not involve dysfunction of language (aphasia) and perception (agnosia and apraxia). Research strategies are proposed to examine the concept of subcortical dementia, an entity that remains controversial and not well understood. The subcortical dementias may constitute a group of partially treatable forms of dementia.