Neural Correlates of Item and Item-Context Memory Encoding

Abstract

The neural correlates of the formation of episodic memories -- or memory for an item and its context -- have been studied using a functional neuroimaging procedure known as the 'subsequent memory procedure'. In this procedure, neural activity associated with later remembered versus later forgotten study items is contrasted and the identified brain regions -- demonstrating 'subsequent memory effects' -- can be considered candidate loci of neurocognitive operations supporting successful episodic encoding. The aim of the present work was to disambiguate the neural correlates of item and item-context (source) memory encoding, and investigate age-related differences in subsequent memory effects as well as the relationship between such effects and memory performance. The findings reported in Chapter 2 investigated whether age-related attenuation of negative subsequent item and item-item memory effects extends to the encoding of item-context memories. It is demonstrated that, unlike negative effects for item and item-item memory, encoding of negative effects for item-context associations does not attenuate with age and the level of disengagement of neural regions promotes better memory performance. The findings reported (from the same fMRI experiment as Chapter 2) in Chapter 3 addressed the question of whether the phenomenon of age-related over-recruitment of frontal regions during encoding extends to encoding of non-verbal materials. It is found that, contrary to prior studies utilizing verbal materials, recruitment of the right frontal cortex in task-stimuli combinations that promote bilateral effects in young subjects is beneficial for memory encoding. The experiment in Chapter 4 aimed to elucidate differences in the encoding of different context types. The results of this study suggest that negative effects differ depending on the type of source feature being encoded. The findings from these studies shed light on the circumstances under which older adults benefit from engagement/disengagement of different neural regions and the circumstances in which age-related changes in subsequent memory effects are observed.