> Top-down modulation

Cognitive Aging

Importance of studying cognitive aging.
Individuals over 65 years of age currently make up more than 13% of the American population. Over the next 25 years, this percentage will double and the number of senior adults is expected to swell to 70 million (26, 27). This dramatic increase in the size of the older population will have far-reaching societal consequences. Although neuroscience research has focused on severe forms of age-related deterioration seen in dementia, cognitive decline in non-demented seniors is pervasive and even a mild deficit in cognition can severely constrain an otherwise productive life and reduce independence. Cognitive deficits are a cause of great distress to many older adults who feel that their ability to lead high-quality lives is negatively impacted by this decline, and it is often considered the most debilitating aspect of aging (28). Understanding the impairments in neural mechanisms that underlie cognitive deficits, as well as the compensatory changes that allow many older adults to remain cognitively intact, is an important step in alleviating this burden and delaying or preventing debilitating functional decline and dementia.

Experimental approach to studying cognitive aging.
Impairments in the cognitive abilities of many older adults are a well-documented phenomenon; a substantial body of research has revealed performance deficits in multiple cognitive domains, such as working memory, long-term memory and attention (reviews; (29, 30)). These deficits appear to be an aspect of the "normal" aging process that occur in the absence of extensive pathology, such as Alzheimer’s disease. Despite heterogeneity in the nature and severity of decline in the older population, common features have been observed with neuropsychological testing, e.g., decreases in processing speed (31) and an inability to effectively filter irrelevant information (32). In addition to cognitive testing, another approach for generating principles that account for the diversity of deficits associated with cognitive aging is to search for  alterations in neural mechanisms that are underlie a wide variety of cognitive abilities (e.g., top-down modulation). The tools of cognitive neuroscience (e.g., PET, fMRI, EEG and TMS) are now being applied to investigate not just how the brain functions, but how it changes with normal aging and how these changes lead to deficits in cognitive abilities.

> Top-down modulation