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Title: Processing speed in aging brain : a functional MRI study using simple stimulus-response mapping task
Authors: Wong, Ho Yin
Degree: Ph.D.
Issue Date: 2019
Abstract: Processing speed mediates cognitive declines due to aging. However, the neurophysiological mechanisms that compromise processing speed remain understudied. In addition, the processing-speed paradigms employed in existing studies may be confounded by sensory, motor, and executive functions, especially among old participants. In this study, a set of simple stimulus-response mapping tasks in two perceptual modalities were used to establish the contribution of functional activation and connectivities on processing speed in young and old participants; the aim was to minimize the influences of the sensory, motor, and executive functions. This study further divided processing speed into decision and non-decision components to characterize the contributions of the neurophysiological properties. The most significant set of predictors were then identified in both the young and older groups to facilitate comparisons between those groups. The final sample included 34 young (aged 18-28) and 20 old (aged 65-75) healthy adults. This study employed visual and audial forms of a stimulus-response mapping task at two levels of difficulty and with a simple response-time task to control for the sensorimotor-related processes. The processing time index (PTI), sensorimotor time index (STI) and cognitive time index (CTI) were statistically derived from reaction-time (RT) measures. Common regions of interests (ROIs) were identified for all the experimental conditions using anatomically defined brain parcellations. Estimated time series for these brain activations were then extracted, as were the effective connectivities. Multivariate structural autoregression was applied to all time series and all ROI (separately for each subject and for each task condition). Bootstrapped mixed-effect lasso (least absolute shrinkage and selection operator) regressions were employed to select the local activations and the interregional effective connectivities so as to predict the values of the three speed indices. For both groups, the bilateral regions of the medial frontal cortex (MFC), anterior insula, superior frontal junction (SFJ), intraparietal sulcus, and cerebellum were activated in all mapping tasks; 13 total ROIs were selected. In the younger group, three local activation predictors and seven effective connectivities were associated with at least one of the three speed indices. Nearly all of these were associated with the right superior MFC and the cerebellum vermis VI and VII; only one causal influence was associated with the right SFJ and the left intraparietal sulcus, as reflected by decision speed (CTI). In the older group, seven activation predictors and five connectivity predictors were associated with speed indices. The predictors associated with the bilateral SFJ and bilateral intraparietal sulcus were unique to the older group. The younger participants' processing speed was supported by the regions related to the MFC (which was implicated in sustained cognitive control), the vermis (which was presumably the automatic counterpart of different frontal functions), and the connection from the left SFJ to the left anterior intraparietal sulcus (which facilitated stimulus-response mapping). The MFC and vermis were also strong predictors of processing speed in the older group. However, the association in the vermis VI/VII/VIII demonstrated incompatible pattern, reflecting a cerebellar adaptive function in the older group. In addition, a more diverse network involving the SFJ and the intraparietal sulcus was also associated with the speed indices, suggesting that the older group engaged the attention function more than the younger group did.
Subjects: Hong Kong Polytechnic University -- Dissertations
Aging -- Physiological aspects
Human information processing -- Age factors
Pages: xi, 99 pages : color illustrations
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