Browsing by Subject "FMRI"
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Item Altered functional connectivity during working memory performance in older adults following low-level laser therapy(2020-08-13) Hickson, Brennan Ouida; Haley, Andreana P.; Harden, Kathryn PMost current interventions for improving cognition in older adults have proven unsuccessful in producing enduring effects, though non-invasive brain stimulation techniques including low-level laser therapy (LLLT) show promise in this regard. The aim of the present study was to determine whether or not physiological changes involving the right superior frontal gyrus, following its stimulation via LLLT, could induce changes in working memory, as measured by a multilevel in-scanner N-back task. Ninety-eight adults (ages 45 and over) with (n = 36) and without (n = 62) mild cognitive impairment were included in this study. It was hypothesized that, relative to adults receiving placebo, individuals treated with LLLT would exhibit strengthened load-dependent functional coupling between this region and other brain regions involved in WM leading to better performance accuracy and faster reaction times on the N-back task. Results showed no differences in performance accuracy (t = 1.02, p = 0.312) or reaction times (t = -0.82, p = 0.413) between treatment groups. Functional connectivity between the right SFG and bilateral occipital gyri and bilateral precuneus regions was strengthened in those who received LLLT but reduced in the placebo group. The LLLT group exhibited reduced functional coupling between the right SFG and paracentral lobule, cingulate cortex, precentral gyrus, middle frontal gyrus, and insula, whereas these connections were strengthened in the placebo group. The absence of change on behavioral outcome measures makes it difficult to contextualize these physiological changes, but the findings seem to suggest excessive engagement in the task following treatment, as well as insufficient deactivation of the default mode network. Follow-up studies are necessary to determine the capacity of LLLT to improve cognition in other domains not investigated by the present study. As well, further insight into the potential of LLLT could be gained through investigations of LLLT in conjunction with cognitive training interventions, as is often the case with alternative neurostimulation therapies.Item Prospective effort and choice(2014-12) Malecek, Nicholas John; Poldrack, Russell A.; Huk, Alexander C.; Beer, Jennifer; Maddox, Todd; Lewis-Peacock, JarrodWe constantly face the challenge of selecting among actions in pursuit of our goals. Behavioral theories suggest the ubiquity of these choices necessitate a valuation process that integrates expected costs and outcomes. Increased sensitivity to costs in value-based choices, such as reduced willingness to tolerate risk, wait or work for rewards, features prominently in the symptomatology of mental illness. Contrary to classical theories of choice that do not distinguish among cost type, the recent unification of experimental economics, psychology and neuroscience describes the influence of specific costs upon behavioral and neural correlates of subjective value. Despite substantial progress in the understanding of the basis of subjective valuation under delay and risk, the specific influence of effort, the energetic cost of an action, remains largely unknown. Limited existing accounts hypothesize that cost sensitivity during subjective valuation results from separable neural systems related to risk, delay and effort. This dissertation evaluates evidence for distinct neural representation of effort and presents a set of experiments designed to refine normative accounts of effort-based choice. First, I review the neural basis of economic choice under risk and delay. Second, I review limited accounts economic choice under effort. I describe a novel prospective effort task designed and validated to examine effort-based valuation and address potential confounds present in previous studies. In the first experiment, I report novel evidence for discounting of neural activity related to value by prospective effort and conjoint sensitivity to effort costs and expected outcomes in brain regions related to selection and generation of actions. In a second experiment, I examined the influence of prospective effort costs upon delay discounting preferences. This experiment did not find modulation of individual preferences by prospective effort costs. Finally, I discuss our results in the context of existing accounts and potential extensions of the prospective effort paradigm. Overall, I show that prospective effort imposes a specific cost, reflected in behavioral and neural correlates of value, and presents a novel approach to further the understanding of motivated behavior.