The Nicotinic Cholinergic System and Cognitive Aging

Overview

Prior research has shown that a chemical system in the brain called the cholinergic system is primarily responsible for cognitive symptoms seen in people with dementia. While therapeutic benefits are clear in dementia, what remains uncertain is the role that the cholinergic system in general and a subset of receptors called the nicotinic system plays in cognition in healthy non-demented older adults (referred to as normal cognitive aging). This is critical because the ever growing healthy aging population will show declines in cognition that fall short of dementia but still impact functional abilities and independence. Maintaining good nicotinic system functioning throughout adulthood may lessen the cognitive symptoms of aging. At this time, it is not clear what the biological cause of age-related changes in cognition is. This study will examine the role of the nicotinic system in the healthy aging brain and examine its role in memory and thinking processes in older and younger adults.

The cholinergic system has been shown to be the primary neurotransmitter system responsible for cognitive symptoms in dementia. While therapeutic benefits are clear in dementia, what remains uncertain is the role that the cholinergic system in general and the nicotinic system specifically plays in cognition in healthy non-demented older adults (referred to as normal cognitive aging in this application). This is critical because the expansion of the healthy aging population will nonetheless show declines in cognition that fall short of dementia but still impact functional abilities and independence. Understanding the effects of age-related functional changes on the nicotinic system will elucidate one neurochemical mechanism underlying age-related changes in cognition and will provide information about how nicotinic dysfunction affects cognition in healthy older adults. Prior research has shown that the nicotinic system has a roll in attention and memory in healthy adults. More recently, with the increased use of brain functional magnetic resonance imaging (fMRI) in combination with psychopharmacological manipulations, data patterns have emerged that further define the role of the nicotinic system in cognition, aging, and dementia. The investigators propose that nicotinic system changes are responsible for age differences in working memory task performance and brain activation. The investigators can observe the functioning of the nicotinic system by examining brain activation patterns in response to nicotinic blockade and stimulation. Increased dorsolateral prefrontal cortex (DLPFC) activation has been shown for older adults compared to younger adults and is hypothesized to be a compensation response for the aging process. The investigators propose that temporary antagonism of the nicotinic system will also produce increased DLPFC activation. However, the relationship between this increased activation and performance will be in different directions for older and younger adults. In older adults, the increased activation will be positively correlated with performance because it is a compensatory response. In younger adults, the increased activation will be negatively correlated with performance because it is a non-adaptive response to the temporary nicotinic antagonism. Nicotinic stimulation in older adults will reveal decreased DLPFC activation that will be negatively correlated with performance and this represents the "younger" pattern of the performance and activation relationship. The younger adults will have a similar pattern of activation and performance as the older adults after nicotinic stimulation because they are already performing optimally and will not receive any further enhancement. These data will further the understanding of a neurochemical mechanism involved in normal aging and how brain activation patterns relate to receptor function.