Neurochemical changes in the aging human brain: implications for behavioral impairment and neurodegenerative disease.

Neurotransmission is impaired in age-related disorders, such as Alzheimer's and Parkinson's diseases, which has prompted many investigations into the neurochemistry of the aging human brain. Of all the neurotransmitter systems studied, age-related changes in parameters of the serotonergic, cholinergic, and dopaminergic systems are the most reliably measured. The association of these neurotransmitters, respectively, with mood, memory, and motor function has fueled interest in how changes in neurochemistry may contribute to age-associated behavioral changes and possibly predispose older persons to diseases of late life. The evidence suggests that impaired neurotransmission may be responsible for at least some of the behavioral abnormalities associated with aging. Moreover, age-related neurodegenerative diseases may evolve from the interaction between defects in specific neurochemical mechanisms and as-yet undefined pathophysiologic processes.