UCLA

The executive control of declarative memory is the goal-directed and volitional manipulation of representations from episodic and semantic memory systems and is thought to critically depend on the interactions between prefrontal cortex neural systems and the default mode network (Mitchell & Johnson, 2009; Spreng, Stevens, Chamberlain, Gilmore, & Schacter, 2010; Vincent, Kahn, Snyder, Raichle, & Buckner, 2008). The prefrontal cortex system itself is thought to be organized hierarchically along a rostrocaudal axis where increasingly anterior prefrontal cortex regions enact and represent more abstract executive control while more posterior frontal cortex regions exert progressively more concrete executive control interactions with motor systems (Badre & D’Esposito, 2009; Koechlin & Hyafil, 2007). The first chapter of this dissertation provides the background on the fronto-parietal control network and default mode network neural systems that govern the executive control of declarative memory (Andrews-Hanna, 2012; Fox et al., 2005; Power et al., 2011; Vincent et al., 2008). The second chapter discusses research focused upon further understanding how rostrolateral prefrontal cortex, the most anterior prefrontal region, interacts with neural systems involved in declarative memory, to enable episodic retrieval and analogical reasoning. The first section of Chapter 2 discusses an fMRI study that was performed to disentangle the role of rostrolateral prefrontal cortex in episodic memory retrieval and analogical reasoning and presents data showing that this brain region is domain-general in nature and functionally couples with domain-specific neural systems for goal-directed cognition (Westphal, Reggente, Ito, & Rissman, 2016). The second section of Chapter 2 presents data from a transcranial direct current stimulation study that causally influenced the stimulation levels of rostrolateral prefrontal cortex during the memory and reasoning tasks and presents evidence that the stimulation of the fronto-parietal control and default mode networks simultaneously improves episodic memory retrieval. The third chapter discusses research focused on further understanding the fronto-parietal control and default mode network neural systems. The first section of Chapter 3 discusses an fMRI study that assessed whole-brain functional connectivity during reasoning and memory tasks and shows that performance in episodic memory retrieval benefits from more whole-brain connectivity, in contrast to reasoning (Westphal, Wang, & Rissman, 2017). The second section of Chapter 3 presents data from a behavioral study that was inspired from work showing that major depressive disorder is associated with aberrant connectivity between the fronto-parietal and default mode networks (Hamilton, Chen, & Gotlib, 2013; Marchetti, Koster, Sonuga-Barke, & De Raedt, 2012), where the retrieval of negatively-valenced autobiographical memories interferes with an ensuing visual working memory task. The fourth chapter summarizes the main findings from each research study and provides some concluding thoughts on what this body of work has revealed about the neurocognitive control processes that support declarative memory.