To date, research on cognitive aging has treated attention as a unitary resource that operates according to a single mechanism of top-down selection. However, contemporary theoretical models of attention propose that it is a distributed resource, embedded in distinct cortical subsystems, and operates in a manner that reflects the properties of those subsystems. For instance, perceptual attention is thought to originate in posterior sensory subsystems and filter competing unattended input prior to encoding, resulting in early selection of attended information. Executive attention, by contrast, is thought to originate in frontal control subsystems and filter unattended input after encoding, resulting in late selection of attended information.
Guided by a distributed resource model, the work described here focuses on how healthy advanced aging influences early selection mechanisms embedded in posterior subsystems, perceptual encoding, and the relationship with frontal subsystems mediating late selection. To examine perceptual attention in isolation, object discrimination tasks were devised in which perceptual competition between repeated objects was manipulated while holding demand on executive control constant. Cortical mechanisms of early selection were probed using functional magnetic resonance imaging (fMRI) indices of neural response and adaptation. Evidence of an age-related impairment in early selection was detected across two fMRI experiments. Unlike young adults, unattended objects not only interfered with perceptual encoding in older adults, but were co-encoded along with the contents of attended input. Age impairments in early selection were also associated with greater reliance on frontally-mediated late selection resources, and, reduced functional connectivity with basal forebrain nuclei. In sum, the results indicate that with increasing age, frontal control subsystems become increasingly encumbered with compensatory redistribution of function from the perceptual cortices, possibly due to loss of central cholinergic integrity. Many well-described age-related deficits of executive attention may therefore represent a consequence of impaired early selection, rather than its cause.
| Identifer | oai:union.ndltd.org:TORONTO/oai:tspace.library.utoronto.ca:1807/34878 |
| Date | 19 December 2012 |
| Creators | Schmitz, Taylor W. |
| Contributors | De Rosa, Eve |
| Source Sets | University of Toronto |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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