Description
Studies have shown that older adults may demonstrate impairments in episodic memory. A decline in episodic memory, or the ability to encode and retrieve events into a spatial and temporal context, is a hallmark cognitive deficit associated with aging. Pattern separation is a neural mechanism that may serve to reduce interference among overlapping representations of similar stimuli in memory. This process may be critical to the formation and retrieval of episodic memories. The hippocampus supports the operation of a pattern separation mechanism to orthogonalize visuospatial input into discrete representations for accurate encoding and retrieval. Increased interference and decreased efficiency in pattern separation could represent a key processing deficit associated with aging. APOE _4 is a plasma protein involved in lipid transportation throughout the brain via cerebral spinal fluid that has been implicated as a genetic risk for developing Alzheimer's disease (AD). It has been shown to bind to beta amyloid, which is the principal component of neuritic plaques found in brains of patients with AD. APOE _4 positives show memory impairment relative to negatives, particularly in the domain of episodic memory. Furthermore, APOE _4 is associated with reduced hippocampal volume in cognitively normal APOE _4 positives, particularly in the dentate gyrus and CA-3 sub-regions. The present study sought to compare the performance of cognitively normal older adults (65+) classified as either APOE _4 positive (n = 21) or negative (n = 21), and younger adults (n = 30) on a spatial pattern separation task that involved varying degrees of spatial interference. During the sample phase, participants were asked to remember the location of a circle on a screen. After a brief delay, the participant was asked to identify the correct location of the original circle when presented simultaneously with two circles (a target and a foil). The distance between the two choice phase circles varied parametrically, as they were separated by one of four spatial separations: 0 cm, 0.5 cm, 1.0 cm, and 1.5 cm. Younger adults and older APOE _4 negatives were predicted to perform significantly better on the spatial pattern separation task compared to older APOE _4 positives. However, the present analyses revealed no significant differences on the spatial pattern separation task among younger adults, _4 positive older adults, and _4 negative older adults. Although the present findings suggest that the presence of the _4 allele may not adversely affect spatial pattern separation in cognitively normal older adults, future studies involving larger samples are needed to further examine the effect of the _4 allele on pattern separation.
