The Relationship between Cerebrovascular Reserve Capacity and Processing Speed: Effects of Complexity, Context and Response Modes

Background: Slowness in cognitive processing speed is common phenomenon in patients with brain damage as well as normal aging. Studies suggest cerebral infarcts, leukoaraiosis, and cerebral hypoperfusion can compromise cerebrovascular reserve capacity (CRC) as being reflected on MRI perfusion. Impaired CRC is strongly related to cognitive dysfunction. We have found cognitive processing speed is particularly sensitive to CRC impairment. However, the conceptualization of processing speed has been controversial, as it is liable to be affected by task complexity, context, and response mode. We intend to adopt a model of processing speed, which is potentially useful in bypassing the limitations embedded in speeded tasks, to examine the relationships between CRC status and processing speed, and to investigate whether CRC parameters can be of help to elucidate the effects of complexity, context, and response mode on speed performance. Methods: We intend to recruit volunteers and patients with unilateral carotid artery stenosis (CAS) for this 3-year project. The reasons for recruiting volunteers are to validate the tasks of processing speed, as parts of the tasks need to be developed. Thus, the data of young and older volunteers (30 in each group) will be used to test the applicability of the speeded tasks. In addition, the speed performance of the older volunteer can also serve as a reference group. Patients with unilateral CAS and wish to undergo carotid stenting procedure will be recruited from the Neurology Department. They will be divided into two groups (left versus right, n = 30 in each group), depending on which side of the carotid is significantly affected. For the patients who decline the revascularization treatment, essential medications will be prescribed, and they will be assigned to the medication group (n = 30). All clinical participants will undergo two testing phases, pre-treatment and 6 months after treatment. The cognitive assessment entails testing of general intelligence, memory, attention, executive functions and processing speed (tasks will be varied in complexity, context, and response mode) by paper-and-pencil and/or computerized tests. Both diffusion- and perfusion-weighted MRI will be used to assess CRC for deriving relevant parameters of perfusion status and rating the severity of infarcts and leukoaraiosis in three phases: pre-treatment, and 1 week and 6 months after treatment. The stroke risk factors and relevant information will also be recorded from patients’ medical notes. Data analyses: The data obtained from cognitive assessment in three patient groups will be analyzed by ANOVA or ANCOVA with repeated measure. The reaction times on each condition of different speeded tasks will be correlated with the CRC parameters across different regions of the brain. The general speed index will also be derived from all the reaction times on each task. Hierarchical multiple regression will be applied by using stroke risk factors, severity of infarcts and leukoaraiosis, and regional perfusion parameters as predictor variables, and reaction times and speed index as criterion variable to examine the contributions of these predictors to processing speed. Expected outcomes: We predict that when a task is speeded, the variation in cognitive performance on different kind of the test can be accounted for by a general speed factor. The assessment of CRC may be of help to elucidate the neural correlates of the cognitive changes or changes in processing speed.

Project ID:PF10401-0547
External Project ID:MOST103-2410-H182-002-MY2