ABSTRACT: Numerous cognitive abilities, including episodic memory, fluid intelligence and executive function. Even the more modest cognitive impairment typical of healthy people as they reach their 70’sand 80’s can negatively impact quality of life. Moreover, the neuropathology associated with dementia onsets years before the emergence of significant clinical symptoms. This long prodromal period places a premium on early detection of trajectories of ‘unsuccessful’ brain aging. For these reasons, it is important to understand the neural bases of the effects of age on cognitive abilities. The present research aims to elucidate factors contributing to age-related differences in the precision with which perceptual and, possibly conceptual, information is represented in the brain. It has been proposed that age-related neural dedifferentiation – a reduction with age in the selectivity and precision of neural representations – plays a critical role in cognitive aging. We propose a series of studies to identify the potential neural mechanisms and functional significance of this phenomenon. One strand of the research will examine whether the precision and variance of the patterns of neuronal activity elicited by individual stimuli differs with age, as is predicted in an influential theoretical framework. We will also determine whether dedifferentiation for individual stimuli is associated with related reductions in neural selectivity for different stimulus categories. A second strand builds on animal and human research showing that neural selectivity for perceptual stimuli is modulated by task demands. A third strand will determine whether the age-related neural dedifferentiation observed for simple perceptual stimuli extends to complex cognitive tasks, namely, different semantic judgments. In a fourth strand of the research, we will identify whether measures of neural dedifferentiation are associated with individual differences in brain structure and cognitive performance. A final strand will use scalp EEG to examine the temporal dynamics of age-related neural dedifferentiation. Within this strand, we aim to determine if neural differentiation emerges later in time in older relative to younger adults, and if age-related increases in ‘neural noise’ contribute to age-related neural dedifferentiation.