The Dissociation of Location and Object Working Memory using fMRI and MEG

iii DEDICATION To my parents who always pushed me to do better and work harder. Your encouragement and support gave me the confidence to accomplish all that I have today. To my friends and family who have supported me with the utmost encouragement and patience. iv ACKNOWLEDGMENTS First and foremost, I would like to thank my mentors, Dr. Andrew Papanicolaou and Dr. Anthony Wright, for their unwavering guidance and encouragement from the moment we first met. They provided me with the knowledge, support, and tools I needed to accomplish my goals. Through everyone's support, I never stopped learning and things always seemed to get easier. Ponnada Narayana for their guidance and suggestions as members of my supervisory committee. Visual working memory (VWM) involves maintaining and processing visual information, often for the purpose of making immediate decisions. Neuroimaging experiments of VWM provide evidence in support of a neural system mainly involving a fronto-parietal neuronal network, but the role of specific brain areas is less clear. A proposal that has recently generated considerable debate suggests that a dissociation of object and location VWM occurs within the prefrontal cortex, in dorsal and ventral regions, respectively. However, re-examination of the relevant literature presents a more robust distribution suggestive of a general caudal-rostral dissociation from occipital and parietal structures, caudally, to prefrontal regions, rostrally, corresponding to location and object memory, respectively. The purpose of the present study was to identify a dissociation of location and object VWM across two imaging methods (magnetoencephalography, MEG, and functional magnetic imaging, fMRI). These two techniques provide complimentary results due the high temporal resolution of MEG and the high spatial resolution of fMRI. The use of identical location and object change detection tasks was employed across techniques and reported for the first time. vi Moreover, this study is the first to use matched stimulus displays across location and object VWM conditions. The results from these two imaging methods provided convergent evidence of a location and object VWM dissociation favoring a general caudal-rostral rather than the more common prefrontal dorsal-ventral view. Moreover, neural activity across techniques was correlated with behavioral performance for the first time and provided convergent results. This novel approach of combining imaging tools to study memory resulted in robust evidence suggesting a novel interpretation of location and object memory. Accordingly, this study presents a novel context within which to explore the neural substrates of WM across imaging techniques …