FMRI Investigation of Spatial Memory Abilities in Individuals Living With Schizophrenia Spectrum Disorders
thesisposted on 23.05.2021, 11:32 by Leanne K. Wilkins
Different strategies dependent on different brain regions may be spontaneously adopted to solve most spatial memory and navigation tasks. For this dissertation, I used brain-imaging and cognitive tasks to test the hypothesis that individuals living with schizophrenia spectrum disorders (SSD) have selective hippocampal-dependent spatial memory impairment. A hippocampal-dependent spatial strategy (locale/allocentric/cognitive map/viewpoint-independent) involves relying on learning the relations between landmarks in the environment, whereas a response strategy (taxon/egocentric/viewpoint-dependent) is more associated with caudate function and involves learning a sequence from a single starting position. In Experiment 1, I examined performance and brain activation with fMRI during the 4-on-8 virtual maze (4/8VM) to test the hypothesis of intact response versus impaired spatial memory in SSD. The SSD participants who adopted a spatial strategy performed more poorly and had less hippocampal activation than other groups. In Experiment 2, I further examined these data using multivariate PLS (partial least squares) analyses to identify whole-brain patterns of activation associated with group and strategy differences on the 4/8VM. Results revealed clusters of correlated activation within the temporal lobe unique to the SSD-Spatial group. The SSD Response group activated the same regions as the Healthy groups, but to a greater extent suggesting over-activation. In contrast to the between-subjects nature of strategy differences on the 4/8VM, for Experiment 3 I used the Courtyard Task to seek converging evidence of a selective hippocampal-dependent impairment in spatial memory using a within-subjects design. The Courtyard Task has previously demonstrated impaired performance among individuals with hippocampal lesions under shifted-view (allocentric) but not same-view (egocentric) conditions. Consistent with a profile of hippocampal dysfunction, the SSD group demonstrated a particular deficit under the shifted-view condition. The results support the development of protocols to train impaired hippocampal-dependent abilities and harness non-hippocampal dependent intact abilities. Overall, this dissertation provides valuable information characterizing spatial memory and highlights the importance of strategy use in SSD.