The present research examined whether eye movements during retrieval capture the relation between... more The present research examined whether eye movements during retrieval capture the relation between an event and its temporal attributes. In two experiments (N=76), we found converging evidence that eye movements reflected the veridicality of memory for temporal order seconds before overt memory judgments, suggesting that these movements captured indirect access to temporal information. These eye movements did not entirely depend on the amount of contextual cueing available (Experiment 1) and reflected the unique ordinal position of an event in a sequence (Experiment 2). Based on our results, we conclude that eye movements reflected the absolute temporal order of past events.
Memory decision‐making in 26‐ to 32‐month‐olds was investigated using visual‐paired comparison pa... more Memory decision‐making in 26‐ to 32‐month‐olds was investigated using visual‐paired comparison paradigms, requiring toddlers to select familiar stimuli (Active condition) or view familiar and novel stimuli (Passive condition). In Experiment 1 (N = 108, 54.6% female, 62% White; replication N = 98), toddlers with higher accuracy in the Active condition showed reduced novelty preference in that condition, but not in the Passive condition (d = −.11). In Experiment 2 (N = 78; 52.6% female; 70.5% White), a brief 5% increase in target size boosted gaze transitions across conditions (d = .50) and accuracy in the Active condition (d = .53). Overall, evidence suggests that better attentional distribution can support decision‐making. Research was conducted between 2014 and 2020 in Northern California.
Nonhuman research has implicated developmental processes within the hippocampus in the emergence ... more Nonhuman research has implicated developmental processes within the hippocampus in the emergence and early development of episodic memory, but research in humans has been constrained by the difficulty of examining hippocampal function during early development. In the present study, we assessed 48 2-year-olds with a novel paradigm in which participants completed two games on a tablet that required remembering associations between unique characters, the places they visited, and the temporal order with which they did so. At the completion of each game, a unique, novel song played. Toddlers remembered spatial locations better than temporal order during an immediate test, after a 20-minute delay, and after a week delay. After the last behavioral session, toddlers underwent an fMRI task during natural nocturnal sleep evaluating hippocampal activation in response to learned and novel songs. We found that the extent of hippocampal activation for learned songs compared to novel songs during sleep was correlated with memory for temproal order across all time delays, but not with memory for spatial locations. The results confirm that that the functional contribution of the hippocampus to early memory can be assessed during sleep and suggest that assessment of temporal aspects of memory in the current task best capture this contribution.
The current study investigated longitudinal change in hippocampal and prefrontal contribution to ... more The current study investigated longitudinal change in hippocampal and prefrontal contribution to episodic retrieval. Functional neuroimaging data were collected during an item-context association memory task for children between the ages of 8 and 14 with individuals scanned 1-3 times over the course of 0.75-3.7 years (Timepoint 1 N = 90; Timepoint 2 N = 83, Timepoint 3 N = 75). We investigated developmental changes in functional activation associated with episodic retrieval (correct item-context > incorrect item-context contrast) and asked whether pubertal changes contributed to developmental changes in pattern of activation. Non-linear developmental trajectories were observed. In the hippocampus, activation decreased with age during childhood and then increased into early adolescence. In the dorsolateral prefrontal cortex, activation was largely absent initially, but quickly accelerated over time. Independent of age, changes in pubertal status additionally predicted increases in item-context activation in initially older children, and decreases in initially younger children across both regions and two indicators of puberty: the Pubertal Development Scale and salivary testosterone. These findings suggest that changes in both age and pubertal status uniquely contribute to memory-related activation, and the timing of pubertal onset may play an important role in the neural mechanisms supporting memory retrieval.
The hippocampus is critically involved in episodic memory, yet relatively little is known about h... more The hippocampus is critically involved in episodic memory, yet relatively little is known about how the development of this structure contributes to the development of episodic memory during middle to late childhood. Previous research has inconsistently reported associations between hippocampal volume and episodic memory performance during this period. We argue that this inconsistency may be due to assessing the hippocampus as a whole, and propose to examine associations separately for subregions along the longitudinal axis of the hippocampus. In the present study, we examined age-related differences in volumes of the hippocampal head, body, and tail, and collected episodic memory measures in children ages 8-11 years and young adults (N = 62). We found that adults had a smaller right hippocampal head, larger hippocampal body bilaterally, and smaller right hippocampal tail compared with children. In adults, but not in children, better episodic memory performance was associated with smaller right hippocampal head and larger hippocampal body. In children, but not in adults, better episodic memory was associated with larger left hippocampal tail. Overall, the results suggest that protracted development of hippocampal subregions contribute to agerelated differences in episodic memory.
The goal of the present study was to investigate whether hippocampal contribution to episodic mem... more The goal of the present study was to investigate whether hippocampal contribution to episodic memory retrieval varies as a function of age (8-9 versus 10-11 versus adults), performance levels (high versus low) and hippocampal sub-region (head, body, tail). We examined fMRI data collected during episodic retrieval from a large sample (N = 126). Participants judged whether a stimulus had been encoded previously, and, if so, which of three scenes it had been paired with (i.e., source judgment). For 8-to 9-years-olds as well as low-performing 10-to 11-year-olds, hippocampal activations did not reliably differentiate between trials on which item-scene associations were correctly recalled (correct source), incorrectly recalled (incorrect source), or trials on which the item was forgotten (miss trials). For high-performing 10-11-year olds and low-performing adults, selective hippocampal activation was observed for correct source relative to incorrect source and miss trials; this effect was observed across the entire hippocampus. For high-performing adults, hippocampal activation also distinguished between correct and incorrect source trialsl, but only in the hippocampal head, suggesting that good performance in adults is associated with more focal hippocampal recruitment. Thus, both age and performance are important factors for understanding the development of memory and hippocampal function.
The goal of the present study was to examine age-related differences in hippocampal and cortical ... more The goal of the present study was to examine age-related differences in hippocampal and cortical contribution to episodic retrieval of spatial context in 3 age groups. Children ages 8-9 and 10-11 years old, and adults ages 18-25 (N¼ 48) encoded black and white line drawings appearing either on the right side or the left side of a screen. Functional magnetic resonance imaging (fMRI) data were acquired while participants attempted to recall where each studied drawing had originally appeared. Correct recall of spatial source indicated successful episodic retrieval of spatial context. Activity in head and body of the hippocampus was associated with episodic retrieval in adults, but not in children. In children, individual differences in hippocampal activation for recognition predicted rates of correct spatial recall. Developmental differences were also found in regions in posterior parietal cortex, anterior prefrontal cortex, and insula. Overall, these results support the view that the development of episodic memory is supported by functional changes in the hippocampus as well as cortical regions.
The development of subjective recollection was investigated in participants aged 6-18 years. In E... more The development of subjective recollection was investigated in participants aged 6-18 years. In Experiment 1 (N = 90), age-related improvements were found in understanding of the subjective experience of recollection, although robust levels of understanding were observed even in the youngest group. In Experiment 2 (N = 100), age-related differences were found in subjective recollection during a memory task, suggesting development not only in the ability to reflect on memory states, but also in the informational basis of subjective recollection. Lower understanding of memory states was associated with increased propensity to claim recollection. These results indicate that subjective recollection develops considerably during childhood and suggest that the development of metamemory supports this capacity.
Episodic memory critically depends on the hippocampus to bind the features of an experience into ... more Episodic memory critically depends on the hippocampus to bind the features of an experience into memory. Episodic memory develops in childhood and adolescence, and hippocampal changes during this period may contribute to this development. Little is known, however, about how the hippocampus contributes to episodic memory development. The hippocampus is comprised of several cytoarchitectural subfields with functional significance for episodic memory. However, hippocampal subfields have not been assessed in vivo during child development, nor has their relation with episodic memory been assessed during this period. In the present study, high-resolution T2-weighted images of the hippocampus were acquired in 39 children and adolescents aged 8 to 14 years (M = 11.30, SD = 2.38), and hippocampal subfields were segmented using a protocol previously validated in adult populations. We first validated the method in children and adolescents and examined age-related differences in hippocampal subfields and correlations between subfield volumes and episodic memory. Significant age-related increases in the subfield volume were observed into early adolescence in the right CA3/DG and CA1. The right CA3/DG subfield volumes were positively correlated with accurate episodic memory for item-color relations, and the right CA3/DG and subiculum were negatively correlated with item false alarm rates. Subfield development appears to follow a protracted developmental trajectory, and likely plays a pivotal role in episodic memory development.
Episodic memory, or the ability to form and retrieve conscious memories about specific past event... more Episodic memory, or the ability to form and retrieve conscious memories about specific past events, improves during childhood. Previous adult neuroimaging results indicate a central role of the hippocampus in episodic retrieval, but it is not clear whether the contribution of the hippocampus changes during development. Traditionally, developmental improvements in episodic retrieval have been thought to depend on strategic processes mediated by the prefrontal cortex (PFC), a region that is considered to have a protracted course of development relative to the hippocampus. The primary goal of the present study was to test the hypothesis that the development of episodic retrieval is also associated with changes in hippocampal function. Children ages 8-to 11-years-old and adults ages 18e25 (N ¼ 41) encoded black and white line drawings surrounded by either a green or red border. Functional magnetic resonance imaging (fMRI) data were acquired while participants attempted to recall which colour was originally paired with each drawing. Correct recall of item-colour pairings indicated successful episodic retrieval. Activity in the anterior hippocampus, but not in the posterior hippocampus, was associated with episodic retrieval in adults, whereas activity in the posterior, but not in the anterior hippocampus, was associated with episodic retrieval in children. Developmental differences were also found in regions in anterior lateral PFC and posterior parietal cortex. Overall, these results support the view that the development of episodic memory is supported by functional changes in the hippocampus as well as in other critical cortical regions.
Functional divisions of labor in support of memory have been reported along the anterior–posterio... more Functional divisions of labor in support of memory have been reported along the anterior–posterior axis of the hippocampus. However, little is known about how the developing hippocampus represents associative memories along this axis. The present research employed representational similarity analysis to ask whether developmental differences exist in the extent to which the anterior versus the posterior hippocampus represent features of the context and associative memories. Functional magnetic resonance imaging data were collected during the retrieval phase of an associative recognition task from 8‐year‐olds, 10‐year‐olds, and adults (N = 58). Participants were asked to retrieve pairs of items, which were presented either in the same location as during encoding or in a flipped location. In the anterior hippocampus and only for adults, pattern similarity between the two studied pair conditions was greater than pattern similarity between studied pairs presented in the same location and novel pairs. In contrast, this difference was not significant in the posterior hippocampus. Older, but not younger, children showed a similar, albeit attenuated, similarity pattern to that of adults, but measures of patterns similarity predicted associative recognition across ages. In addition, exploratory analyses showed that similarity patterns in the adult posterior, but not anterior, hippocampus tracked the order of the runs. Overall, the results suggest functional and developmental dissociations in processing different contextual features, with the anterior hippocampus responding to salient and rapid‐changing features and the posterior hippocampus responding to slower‐changing features of the context.
The ability to recollect details about past events improves during childhood. Most researchers fa... more The ability to recollect details about past events improves during childhood. Most researchers favor the view that this improvement depends largely on the development of the prefrontal cortex, which is thought to have a protracted course of development relative to the medial temporal lobes (MTL). The primary goal of the present study was to test the hypothesis that the development of detail recollection is also associated with changes in MTL function. We collected functional magnetic resonance imaging data during an incidental encoding task in 80 participants, divided equally across four age groups: 8-year-olds, 10-to 11-year-olds, 14-year-olds, and young adults. Developmental differences in MTL activation profiles were observed. Fourteen-year-olds and adults engaged regions of the hippocampus and posterior parahippocampal gyrus selectively for subsequent detail recollection, whereas 8-and 10-to 11-year-olds did not. In 8-year-olds, these regions were recruited indiscriminately for detail recollection and item recognition; in 10-to 11-year-olds, activation in these regions did not consistently predict subsequent memory. These results suggest there are changes in the functional organization of the MTL, such that the hippocampus and posterior parahippocampal gyrus become increasingly specialized for recollection; these changes may be in part responsible for long-term memory improvements during childhood.
Infants and toddlers amass a lexicon at a rapid pace and the extent of this development is a stro... more Infants and toddlers amass a lexicon at a rapid pace and the extent of this development is a strong predictor of important future outcomes, including educational achievements. However, little is known about the neural substrates that support early vocabulary learning. Hippocampal and anterior medial-temporal (MTL) processes have been recently hypothesized to support memory for the initial association between new words and their referents, but this hypothesis has not been tested during early child development, when a more dominant role of cortical learning has also been proposed. We assessed 2-year-olds (N = 38) for their memory of newly learned pseudo-words associated with novel objects and puppets. We tested memory for these associations after a 20-minute and a one-week delay. We then played these pseudo-words, previously known words, and completely novel pseudo-words during natural nocturnal sleep, while collecting functional magnetic resonance imaging data. We found that activation in the left hippocampus and left anterior MTL for newly learned words was associated with memory for puppet names at the 20-minute delay, and activation in these same regions for known words compared to novel words was associated with memory for the puppet names at the one-week delay. In addition, activation for newly learned words was associated with productive vocabulary, underscoring that existing vocabulary might support the engagement of hippocampal and MTL mechanisms during learning of new words.
Current opinion in behavioral sciences, Oct 1, 2017
The capacity to integrate various features of an event (e.g. spatial and temporal information) in... more The capacity to integrate various features of an event (e.g. spatial and temporal information) into a bound representation of the event is essential for episodic memory and depends critically on the hippocampus. Item-space and item-time binding operations emerge in infancy, but it is not until the beginning of the third year of life that they afford the ability to retain and flexible reinstate arbitrary associations between events and their spatio-temporal context. Further behavioral improvement occurs from childhood into adolescence. Structural and functional development of the hippocampus has been implicated to explain these changes, but future studies should demonstrate a direct link between behavioral development and hippocampal change.
OBJECTIVE Fluid replacement to correct dehydration, acidosis, and electrolyte abnormalities is th... more OBJECTIVE Fluid replacement to correct dehydration, acidosis, and electrolyte abnormalities is the cornerstone of treatment for diabetic ketoacidosis (DKA), but little is known about optimal fluid infusion rates and electrolyte content. The objective of this study was to evaluate whether different fluid protocols affect the rate of normalization of biochemical derangements during DKA treatment. RESEARCH DESIGN AND METHODS The current analysis involved moderate or severe DKA episodes (n = 714) in children age <18 years enrolled in the Fluid Therapies Under Investigation in DKA (FLUID) Trial. Children were assigned to one of four treatment groups using a 2 × 2 factorial design (0.90% or 0.45% saline and fast or slow rate of administration). RESULTS The rate of change of pH did not differ by treatment arm, but Pco2 increased more rapidly in the fast versus slow fluid infusion arms during the initial 4 h of treatment. The anion gap also decreased more rapidly in the fast versus slow ...
The present research examined whether eye movements during retrieval capture the relation between... more The present research examined whether eye movements during retrieval capture the relation between an event and its temporal attributes. In two experiments (N=76), we found converging evidence that eye movements reflected the veridicality of memory for temporal order seconds before overt memory judgments, suggesting that these movements captured indirect access to temporal information. These eye movements did not entirely depend on the amount of contextual cueing available (Experiment 1) and reflected the unique ordinal position of an event in a sequence (Experiment 2). Based on our results, we conclude that eye movements reflected the absolute temporal order of past events.
Memory decision‐making in 26‐ to 32‐month‐olds was investigated using visual‐paired comparison pa... more Memory decision‐making in 26‐ to 32‐month‐olds was investigated using visual‐paired comparison paradigms, requiring toddlers to select familiar stimuli (Active condition) or view familiar and novel stimuli (Passive condition). In Experiment 1 (N = 108, 54.6% female, 62% White; replication N = 98), toddlers with higher accuracy in the Active condition showed reduced novelty preference in that condition, but not in the Passive condition (d = −.11). In Experiment 2 (N = 78; 52.6% female; 70.5% White), a brief 5% increase in target size boosted gaze transitions across conditions (d = .50) and accuracy in the Active condition (d = .53). Overall, evidence suggests that better attentional distribution can support decision‐making. Research was conducted between 2014 and 2020 in Northern California.
Nonhuman research has implicated developmental processes within the hippocampus in the emergence ... more Nonhuman research has implicated developmental processes within the hippocampus in the emergence and early development of episodic memory, but research in humans has been constrained by the difficulty of examining hippocampal function during early development. In the present study, we assessed 48 2-year-olds with a novel paradigm in which participants completed two games on a tablet that required remembering associations between unique characters, the places they visited, and the temporal order with which they did so. At the completion of each game, a unique, novel song played. Toddlers remembered spatial locations better than temporal order during an immediate test, after a 20-minute delay, and after a week delay. After the last behavioral session, toddlers underwent an fMRI task during natural nocturnal sleep evaluating hippocampal activation in response to learned and novel songs. We found that the extent of hippocampal activation for learned songs compared to novel songs during sleep was correlated with memory for temproal order across all time delays, but not with memory for spatial locations. The results confirm that that the functional contribution of the hippocampus to early memory can be assessed during sleep and suggest that assessment of temporal aspects of memory in the current task best capture this contribution.
The current study investigated longitudinal change in hippocampal and prefrontal contribution to ... more The current study investigated longitudinal change in hippocampal and prefrontal contribution to episodic retrieval. Functional neuroimaging data were collected during an item-context association memory task for children between the ages of 8 and 14 with individuals scanned 1-3 times over the course of 0.75-3.7 years (Timepoint 1 N = 90; Timepoint 2 N = 83, Timepoint 3 N = 75). We investigated developmental changes in functional activation associated with episodic retrieval (correct item-context > incorrect item-context contrast) and asked whether pubertal changes contributed to developmental changes in pattern of activation. Non-linear developmental trajectories were observed. In the hippocampus, activation decreased with age during childhood and then increased into early adolescence. In the dorsolateral prefrontal cortex, activation was largely absent initially, but quickly accelerated over time. Independent of age, changes in pubertal status additionally predicted increases in item-context activation in initially older children, and decreases in initially younger children across both regions and two indicators of puberty: the Pubertal Development Scale and salivary testosterone. These findings suggest that changes in both age and pubertal status uniquely contribute to memory-related activation, and the timing of pubertal onset may play an important role in the neural mechanisms supporting memory retrieval.
The hippocampus is critically involved in episodic memory, yet relatively little is known about h... more The hippocampus is critically involved in episodic memory, yet relatively little is known about how the development of this structure contributes to the development of episodic memory during middle to late childhood. Previous research has inconsistently reported associations between hippocampal volume and episodic memory performance during this period. We argue that this inconsistency may be due to assessing the hippocampus as a whole, and propose to examine associations separately for subregions along the longitudinal axis of the hippocampus. In the present study, we examined age-related differences in volumes of the hippocampal head, body, and tail, and collected episodic memory measures in children ages 8-11 years and young adults (N = 62). We found that adults had a smaller right hippocampal head, larger hippocampal body bilaterally, and smaller right hippocampal tail compared with children. In adults, but not in children, better episodic memory performance was associated with smaller right hippocampal head and larger hippocampal body. In children, but not in adults, better episodic memory was associated with larger left hippocampal tail. Overall, the results suggest that protracted development of hippocampal subregions contribute to agerelated differences in episodic memory.
The goal of the present study was to investigate whether hippocampal contribution to episodic mem... more The goal of the present study was to investigate whether hippocampal contribution to episodic memory retrieval varies as a function of age (8-9 versus 10-11 versus adults), performance levels (high versus low) and hippocampal sub-region (head, body, tail). We examined fMRI data collected during episodic retrieval from a large sample (N = 126). Participants judged whether a stimulus had been encoded previously, and, if so, which of three scenes it had been paired with (i.e., source judgment). For 8-to 9-years-olds as well as low-performing 10-to 11-year-olds, hippocampal activations did not reliably differentiate between trials on which item-scene associations were correctly recalled (correct source), incorrectly recalled (incorrect source), or trials on which the item was forgotten (miss trials). For high-performing 10-11-year olds and low-performing adults, selective hippocampal activation was observed for correct source relative to incorrect source and miss trials; this effect was observed across the entire hippocampus. For high-performing adults, hippocampal activation also distinguished between correct and incorrect source trialsl, but only in the hippocampal head, suggesting that good performance in adults is associated with more focal hippocampal recruitment. Thus, both age and performance are important factors for understanding the development of memory and hippocampal function.
The goal of the present study was to examine age-related differences in hippocampal and cortical ... more The goal of the present study was to examine age-related differences in hippocampal and cortical contribution to episodic retrieval of spatial context in 3 age groups. Children ages 8-9 and 10-11 years old, and adults ages 18-25 (N¼ 48) encoded black and white line drawings appearing either on the right side or the left side of a screen. Functional magnetic resonance imaging (fMRI) data were acquired while participants attempted to recall where each studied drawing had originally appeared. Correct recall of spatial source indicated successful episodic retrieval of spatial context. Activity in head and body of the hippocampus was associated with episodic retrieval in adults, but not in children. In children, individual differences in hippocampal activation for recognition predicted rates of correct spatial recall. Developmental differences were also found in regions in posterior parietal cortex, anterior prefrontal cortex, and insula. Overall, these results support the view that the development of episodic memory is supported by functional changes in the hippocampus as well as cortical regions.
The development of subjective recollection was investigated in participants aged 6-18 years. In E... more The development of subjective recollection was investigated in participants aged 6-18 years. In Experiment 1 (N = 90), age-related improvements were found in understanding of the subjective experience of recollection, although robust levels of understanding were observed even in the youngest group. In Experiment 2 (N = 100), age-related differences were found in subjective recollection during a memory task, suggesting development not only in the ability to reflect on memory states, but also in the informational basis of subjective recollection. Lower understanding of memory states was associated with increased propensity to claim recollection. These results indicate that subjective recollection develops considerably during childhood and suggest that the development of metamemory supports this capacity.
Episodic memory critically depends on the hippocampus to bind the features of an experience into ... more Episodic memory critically depends on the hippocampus to bind the features of an experience into memory. Episodic memory develops in childhood and adolescence, and hippocampal changes during this period may contribute to this development. Little is known, however, about how the hippocampus contributes to episodic memory development. The hippocampus is comprised of several cytoarchitectural subfields with functional significance for episodic memory. However, hippocampal subfields have not been assessed in vivo during child development, nor has their relation with episodic memory been assessed during this period. In the present study, high-resolution T2-weighted images of the hippocampus were acquired in 39 children and adolescents aged 8 to 14 years (M = 11.30, SD = 2.38), and hippocampal subfields were segmented using a protocol previously validated in adult populations. We first validated the method in children and adolescents and examined age-related differences in hippocampal subfields and correlations between subfield volumes and episodic memory. Significant age-related increases in the subfield volume were observed into early adolescence in the right CA3/DG and CA1. The right CA3/DG subfield volumes were positively correlated with accurate episodic memory for item-color relations, and the right CA3/DG and subiculum were negatively correlated with item false alarm rates. Subfield development appears to follow a protracted developmental trajectory, and likely plays a pivotal role in episodic memory development.
Episodic memory, or the ability to form and retrieve conscious memories about specific past event... more Episodic memory, or the ability to form and retrieve conscious memories about specific past events, improves during childhood. Previous adult neuroimaging results indicate a central role of the hippocampus in episodic retrieval, but it is not clear whether the contribution of the hippocampus changes during development. Traditionally, developmental improvements in episodic retrieval have been thought to depend on strategic processes mediated by the prefrontal cortex (PFC), a region that is considered to have a protracted course of development relative to the hippocampus. The primary goal of the present study was to test the hypothesis that the development of episodic retrieval is also associated with changes in hippocampal function. Children ages 8-to 11-years-old and adults ages 18e25 (N ¼ 41) encoded black and white line drawings surrounded by either a green or red border. Functional magnetic resonance imaging (fMRI) data were acquired while participants attempted to recall which colour was originally paired with each drawing. Correct recall of item-colour pairings indicated successful episodic retrieval. Activity in the anterior hippocampus, but not in the posterior hippocampus, was associated with episodic retrieval in adults, whereas activity in the posterior, but not in the anterior hippocampus, was associated with episodic retrieval in children. Developmental differences were also found in regions in anterior lateral PFC and posterior parietal cortex. Overall, these results support the view that the development of episodic memory is supported by functional changes in the hippocampus as well as in other critical cortical regions.
Functional divisions of labor in support of memory have been reported along the anterior–posterio... more Functional divisions of labor in support of memory have been reported along the anterior–posterior axis of the hippocampus. However, little is known about how the developing hippocampus represents associative memories along this axis. The present research employed representational similarity analysis to ask whether developmental differences exist in the extent to which the anterior versus the posterior hippocampus represent features of the context and associative memories. Functional magnetic resonance imaging data were collected during the retrieval phase of an associative recognition task from 8‐year‐olds, 10‐year‐olds, and adults (N = 58). Participants were asked to retrieve pairs of items, which were presented either in the same location as during encoding or in a flipped location. In the anterior hippocampus and only for adults, pattern similarity between the two studied pair conditions was greater than pattern similarity between studied pairs presented in the same location and novel pairs. In contrast, this difference was not significant in the posterior hippocampus. Older, but not younger, children showed a similar, albeit attenuated, similarity pattern to that of adults, but measures of patterns similarity predicted associative recognition across ages. In addition, exploratory analyses showed that similarity patterns in the adult posterior, but not anterior, hippocampus tracked the order of the runs. Overall, the results suggest functional and developmental dissociations in processing different contextual features, with the anterior hippocampus responding to salient and rapid‐changing features and the posterior hippocampus responding to slower‐changing features of the context.
The ability to recollect details about past events improves during childhood. Most researchers fa... more The ability to recollect details about past events improves during childhood. Most researchers favor the view that this improvement depends largely on the development of the prefrontal cortex, which is thought to have a protracted course of development relative to the medial temporal lobes (MTL). The primary goal of the present study was to test the hypothesis that the development of detail recollection is also associated with changes in MTL function. We collected functional magnetic resonance imaging data during an incidental encoding task in 80 participants, divided equally across four age groups: 8-year-olds, 10-to 11-year-olds, 14-year-olds, and young adults. Developmental differences in MTL activation profiles were observed. Fourteen-year-olds and adults engaged regions of the hippocampus and posterior parahippocampal gyrus selectively for subsequent detail recollection, whereas 8-and 10-to 11-year-olds did not. In 8-year-olds, these regions were recruited indiscriminately for detail recollection and item recognition; in 10-to 11-year-olds, activation in these regions did not consistently predict subsequent memory. These results suggest there are changes in the functional organization of the MTL, such that the hippocampus and posterior parahippocampal gyrus become increasingly specialized for recollection; these changes may be in part responsible for long-term memory improvements during childhood.
Infants and toddlers amass a lexicon at a rapid pace and the extent of this development is a stro... more Infants and toddlers amass a lexicon at a rapid pace and the extent of this development is a strong predictor of important future outcomes, including educational achievements. However, little is known about the neural substrates that support early vocabulary learning. Hippocampal and anterior medial-temporal (MTL) processes have been recently hypothesized to support memory for the initial association between new words and their referents, but this hypothesis has not been tested during early child development, when a more dominant role of cortical learning has also been proposed. We assessed 2-year-olds (N = 38) for their memory of newly learned pseudo-words associated with novel objects and puppets. We tested memory for these associations after a 20-minute and a one-week delay. We then played these pseudo-words, previously known words, and completely novel pseudo-words during natural nocturnal sleep, while collecting functional magnetic resonance imaging data. We found that activation in the left hippocampus and left anterior MTL for newly learned words was associated with memory for puppet names at the 20-minute delay, and activation in these same regions for known words compared to novel words was associated with memory for the puppet names at the one-week delay. In addition, activation for newly learned words was associated with productive vocabulary, underscoring that existing vocabulary might support the engagement of hippocampal and MTL mechanisms during learning of new words.
Current opinion in behavioral sciences, Oct 1, 2017
The capacity to integrate various features of an event (e.g. spatial and temporal information) in... more The capacity to integrate various features of an event (e.g. spatial and temporal information) into a bound representation of the event is essential for episodic memory and depends critically on the hippocampus. Item-space and item-time binding operations emerge in infancy, but it is not until the beginning of the third year of life that they afford the ability to retain and flexible reinstate arbitrary associations between events and their spatio-temporal context. Further behavioral improvement occurs from childhood into adolescence. Structural and functional development of the hippocampus has been implicated to explain these changes, but future studies should demonstrate a direct link between behavioral development and hippocampal change.
OBJECTIVE Fluid replacement to correct dehydration, acidosis, and electrolyte abnormalities is th... more OBJECTIVE Fluid replacement to correct dehydration, acidosis, and electrolyte abnormalities is the cornerstone of treatment for diabetic ketoacidosis (DKA), but little is known about optimal fluid infusion rates and electrolyte content. The objective of this study was to evaluate whether different fluid protocols affect the rate of normalization of biochemical derangements during DKA treatment. RESEARCH DESIGN AND METHODS The current analysis involved moderate or severe DKA episodes (n = 714) in children age <18 years enrolled in the Fluid Therapies Under Investigation in DKA (FLUID) Trial. Children were assigned to one of four treatment groups using a 2 × 2 factorial design (0.90% or 0.45% saline and fast or slow rate of administration). RESULTS The rate of change of pH did not differ by treatment arm, but Pco2 increased more rapidly in the fast versus slow fluid infusion arms during the initial 4 h of treatment. The anion gap also decreased more rapidly in the fast versus slow ...
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Papers by Simona Ghetti