Neuropsychological features of early Alzheimer's disease: preclinical and clinical stages.

In the preclinical stage of Alzheimer's disease (AD), studies of asymptomatic mutation carriers have identified impairments in episodic memory. Other cognitive functions show no or slight impairment suggesting that preclinical AD is a unifunctional cognitive syndrome; the brain is affected selectively and predominantly in the medial temporal structures. In the early clinical stage, deficits occur in episodic memory, verbal abilities, visuospatial functions, attention, and executive functions. AD becomes a multifunctional cognitive syndrome and the brain's association cortices are affected. Nevertheless, sensory-motor performance and procedural memory seem to be intact and only slight impairment may be seen in primary memory. In advanced AD, cognitive dysfunction including deficits is global in primary memory, although sensory-motor performance may be well preserved. The brain's association cortices are severely affected. The sequence of cognitive decline; from unifunctional to global deficits, conforms to the three-stage development of neurofibrillary tangles described by Braak and Braak.