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.
FMRI Investigation of Spatial Memory Abilities in Individuals Living With Schizophrenia Spectrum Disorders
