One of the most intriguing and enduring issues in contemporary developmental cognitive neuroscience centers on the development of the ability to remember past experiences and the neural systems which support this capacity. Over the past 25 years, through methodological advancements and direct challenges to established assumptions, the focus of this developmental question has shifted to highlight the second half of the first year of life as the time when true explicit memory functionally emerges and begins to rapidly develop. The purpose of the following study was to test specific hypotheses regarding the biobehavioral development of explicit memory during infancy and present a new approach to studying the behavioral and physiological expression of this system. This study, which was guided by hypothesized neural substrates of this memory system, is the first direct investigation of continuous brain electrical activity during both the encoding and retrieval phases of explicit memory processing in infants. Memory-related differences in behavior and task-related brain activity in individual cortical areas were of particular interest. The results of this study provided some support for the hypothesis that baseline-to-task changes in EEG power can distinguish between successful and unsuccessful ordered-recall memory. Specifically, decreases in brain-electrical activity relative to a baseline period were found at both frontal and temporal locations during stimulus encoding and retrieval for infants who failed the recall tests. However, either no change, or increases in EEG power at frontal and temporal sites was related to successful performance on this task. In addition, different patterns of brain-electrical activity were present for correct and incorrect responses from the same child. This study contributes to our understanding of the biobehavioral expression of infant explicit memory in three main ways. First, changes in both frontal and temporal lobe activity are directly involved in explicit memory processing both during event encoding as well as retrieval. Second, this work provides evidence of a developmentally appropriate and valid pattern of electrophysiology specific to explicit memory processing. Finally, this study bridges the gap between a classic behavioral task of infant memory (which has been conceptually linked to neuropsychological data) and current developmental cognitive neuroscience. / Ph. D.

The term working memory (WM) refers to a set of cognitive processes that allows for the temporary storage and manipulation of information. Neural correlates of the N- back task, a well-established WM measure used in neuroimaging, have been studied extensively in adults but less so in developmental populations. This thesis determines the effect of age on brain activations that mediate cognitive processes for remembering non- verbal/visual stimuli. Block-design fMRI was used to record activity in 84 subjects (6-35 years) during a visual-patterns 0- and 1-back task. Regions activated during the 1-back condition were largely common to all age groups, with adults displaying the largest extent of activations. Children and adolescents showed similar 0-back activations (distinct from 1-back) while adults engaged an analogous 1-back activation pattern during 0-back, suggesting that brain mechanisms underlying memory and attentional processes required for this task in children and adolescents are not yet mature and that strategy usage is still developing.

The term working memory (WM) refers to a set of cognitive processes that allows for the temporary storage and manipulation of information. Neural correlates of the N- back task, a well-established WM measure used in neuroimaging, have been studied extensively in adults but less so in developmental populations. This thesis determines the effect of age on brain activations that mediate cognitive processes for remembering non- verbal/visual stimuli. Block-design fMRI was used to record activity in 84 subjects (6-35 years) during a visual-patterns 0- and 1-back task. Regions activated during the 1-back condition were largely common to all age groups, with adults displaying the largest extent of activations. Children and adolescents showed similar 0-back activations (distinct from 1-back) while adults engaged an analogous 1-back activation pattern during 0-back, suggesting that brain mechanisms underlying memory and attentional processes required for this task in children and adolescents are not yet mature and that strategy usage is still developing.

There is evidence that language ability is related to a number of cognitive processes, including memory. As children become more proficient language-users, they develop the ability to use language as a memory attribute. This study used EEG coherence to investigate the extent to which verbal encoding strategies account for individual differences in two short-term recognition memory tasks in 50 3-year-olds. Children with better expressive and receptive language performed better on the picture memory task (which contains stimuli that can easily be labeled) but not the abstract memory task, indicating that language may support memory processes for some types of stimuli more than for others. Analyses of EEG coherence at the hypothesized electrode pairs (F7-T3 and F8-T4) at baseline and encoding were not significant, indicating that verbal encoding does not account for individual differences in short-term memory performance. When these electrode pairs were examined at baseline and retrieval for the picture memory task, EEG coherence analyses indicated that it may be the use of language as a retrieval cue rather than an encoding strategy that explains individual differences in short-term recognition memory. / Ph. D.

The present study examined source memory development in a sample of 4 and 6 year children. Patterns of brain electrical (EEG) activity were examined in order to provide a neural basis for the role of prefrontal cortex functioning during source monitoring. Children were taught a series of novel facts from two difference sources (either an experimenter or puppet) and their memory for both item and source information was later tested. Results demonstrated that, after controlling for language, patterns of frontal brain activity predicted 6 year item recall performance, and trends toward significance were observed for temporal brain activity predicting 6 year source recall performance. No associations between frontal or temporal EEG activity and episodic memory judgments were observed among 4-year-old children. Future investigations should examine how source memory, and on a more general level contextual memory binding, influence the development of episodic memory in early childhood. / Master of Science

Seventy-three children participated in an investigation of inhibitory control (IC) at 3 years of age. Child IC was measured under various conditions in order to determine the impact that nonverbal and/or motivational task demands had on child IC task performance. Furthermore, task performance was examined with respect to measures of language, temperament, and psychophysiology. Tasks showed different patterns of relations to each of these variables. Furthermore, performance on the Hand Game, our measure of nonverbal IC, was explained by frontal EEG activity and, surprisingly, by language abilities. In contrast, performance on two other IC tasks, Day-Night and Less is More, was not related to measures of language or frontal EEG, perhaps because children performed at chance level on these tasks, indicating that these tasks may be too difficult for 3-year-old children. Implications of these findings are discussed. / Master of Science

There is evidence that language ability is related to a number of cognitive processes, including memory. This study used EEG to investigate the extent to which verbal encoding strategies account for individual differences in short-term recognition memory performance in 44 3-year-olds. As hypothesized, children with better language ability (as measured by the PPVT-III) performed better on the memory task. Analyses of EEG power at the hypothesized electrode sites were not significant, but the hypothesis that children who perform better on the recognition memory task will use more verbal encoding strategies than children who perform less well was partially supported by EEG coherence analyses. Children in the high memory group had significantly greater frontal-temporal coherence in the left hemisphere (F7-T3) than the low memory group. However, this was true both at baseline and during encoding, implying that children in the high memory group have greater overall connectivity between these brain areas and that they tend to use more verbal strategies than the low memory group, as they interact with their environments in general, not just during a memory task. / Master of Science