Neurite density of the hippocampus is associated with trace eyeblink conditioning latency in 4- to 6-year-olds.

Limited options exist to evaluate the development of hippocampal function in young children. Research has established that trace eyeblink conditioning (EBC) relies on a functional hippocampus. Hence, we set out to investigate whether trace EBC is linked to hippocampal structure, potentially serving as a valuable indicator of hippocampal development. Our study explored potential associations between individual differences in hippocampal volume and neurite density with trace EBC performance in young children. We used onset latency of conditioned responses (CR) and percentage of conditioned responses (% CR) as measures of hippocampal-dependent associative learning. Using a sample of typically developing children aged 4 to 6 years (N = 30; 14 girls; M = 5.70 years), participants underwent T1- and diffusion-weighted MRI scans and completed a 15-min trace eyeblink conditioning task conducted outside the MRI. % CR and CR onset latency were calculated based on all trials involving tone-puff presentations and tone-alone trials. Findings revealed a connection between greater left hippocampal neurite density and delayed CR onset latency. Children with higher neurite density in the left hippocampus tended to blink closer to the onset of the unconditioned stimulus, indicating that structural variations in the hippocampus were associated with more precise timing of conditioned responses. No other relationships were observed between hippocampal volume, cerebellum volume or neurite density, hippocampal white matter connectivity and any EBC measures. Preliminary results suggest that trace EBC may serve as a straightforward yet innovative approach for studying hippocampal development in young children and populations with atypical development.

Volumetric development of hippocampal subfields and hippocampal white matter connectivity: Relationship with episodic memory.

The hippocampus is a complex structure composed of distinct subfields. It has been central to understanding neural foundations of episodic memory. In the current cross-sectional study, using a large sample of 830, 3- to 21-year-olds from a unique, publicly available dataset we examined the following questions: (1) Is there elevated grey matter volume of the hippocampus and subfields in late compared to early development? (2) How does hippocampal volume compare with the rest of the cerebral cortex at different developmental stages? and (3) What is the relation between hippocampal volume and connectivity with episodic memory performance? We found hippocampal subfield volumes exhibited a nonlinear relation with age and showed a lag in volumetric change with age when compared to adjacent cortical regions (e.g., entorhinal cortex). We also observed a significant reduction in cortical volume across older cohorts, while hippocampal volume showed the opposite pattern. In addition to age-related differences in gray matter volume, dentate gyrus/cornu ammonis 3 volume was significantly related to episodic memory. We did not, however, find any associations with episodic memory performance and connectivity through the uncinate fasciculus, fornix, or cingulum. The results are discussed in the context of current research and theories of hippocampal development and its relation to episodic memory.

Temporal and topographical changes in theta power between middle childhood and adolescence during sentence comprehension.

Time frequency analysis of the EEG is increasingly used to study the neural oscillations supporting language comprehension. Although this method holds promise for developmental research, most existing work focuses on adults. Theta power (4-8 Hz) in particular often corresponds to semantic processing of words in isolation and in ongoing text. Here we investigated how the timing and topography of theta engagement to individual words during written sentence processing changes between childhood and adolescence (8-15 years). Results show that topographically, the theta response is broadly distributed in children, occurring over left and right central-posterior and midline frontal areas, and localizes to left central-posterior areas by adolescence. There were two notable developmental shifts. First, in response to each word, early (150-300 msec) theta engagement over frontal areas significantly decreases between 8 and 9 years and 10-11 years. Second, throughout the sentence, theta engagement over the right parietal areas significantly decreases between 10 and 11 years and 12-13 years with younger children's theta response remaining significantly elevated between words compared to adolescents'. We found no significant differences between 12 and 13 years and 14-15 years. These findings indicate that children's engagement of the language network during sentence processing continues to change through middle childhood but stabilizes into adolescence.

Gender differences in mothers' spatial language use and children's mental rotation abilities in Preschool and Kindergarten.

Mental rotation has emerged as an important predictor of success in Science, Technology, Engineering, and Math (STEM). By the age of 4.5 years, boys outperform girls in these abilities. Because parents use less spatial language with girls at this age (Pruden and Levine, 2017), the amount of spatial language that children are exposed to at home is believed to be one potential contributor to this disparity in preschool age children. To date, it is unclear if this gender difference continues when children enter school. To address this question in this study, children not yet in kindergarten (PreK) and kindergarten and first grade children (K+) were recorded playing with their mothers using magnetic tile toys followed by children's completion of a mental rotation task. As expected, mothers used more spatial language with PreK boys than girls; however, this relationship reversed in K+, with mothers using significantly more spatial language with girls than boys. Surprisingly, despite this, boys outperformed girls on the mental rotation task. These findings suggest that although girls' exposure to spatial language is higher after entry into school, this language difference is not reflected in increases in mental rotation abilities. Thus, earlier exposure to spatial language may be vital for the development of mental rotation abilities.

Using the N400 event-related potential to study word learning from context in children from low- and higher-socioeconomic status homes.

Children from low-socioeconomic status (SES) homes have significantly smaller vocabularies than their higher-SES peers, a gap that increases over the course of the school years. One reason for the increase in this vocabulary gap during the school years is that children from low-SES homes learn fewer words from context than their higher-SES peers. To better understand how the process of word learning from context might differ in children related to SES, we investigated changes in the N400 event-related potential (ERP) as children from low- and higher-SES homes learned new words using only the surrounding linguistic context. There were no differences in the N400 response to known words related to SES. In response to the target word being learned, children from higher-SES homes, like adults in previous studies, exhibited an attenuation of the N400 across exposures as they attached meaning to it. Children from low-SES homes did not show this same attenuation. These findings support previous work showing that children from low-SES homes may have differences or more variability in the neural components supporting language processing, and they extend previous work to illustrate how this variability may relate to word learning and, ultimately, vocabulary growth.

Vocabulary knowledge mediates the link between socioeconomic status and word learning in grade school.

The relationship between children's slow vocabulary growth and the family's low socioeconomic status (SES) has been well documented. However, previous studies have often focused on infants or preschoolers and primarily used static measures of vocabulary at multiple time points. To date, there is no research investigating whether SES predicts a child's word learning abilities in grade school and, if so, what mediates this relationship. In this study, 68 children aged 8-15 years performed a written word learning from context task that required using the surrounding text to identify the meaning of an unknown word. Results revealed that vocabulary knowledge significantly mediated the relationship between SES (as measured by maternal education) and word learning. This was true despite the fact that the words in the linguistic context surrounding the target word are typically acquired well before 8 years of age. When controlling for vocabulary, word learning from written context was not predicted by differences in reading comprehension, decoding, or working memory. These findings reveal that differences in vocabulary growth between grade school children from low and higher SES homes are likely related to differences in the process of word learning more than knowledge of surrounding words or reading skills. Specifically, children from lower SES homes are not as effective at using known vocabulary to build a robust semantic representation of incoming text to identify the meaning of an unknown word.