Characterizing Typical Development of Memory Systems in the Brain

Our research aims to characterize how developmental effects in human cognition, and specifically human memory, are enabled and limited by the unfolding of a range of processes of brain development. We use a wide variety of memory paradigms, such as recall and recognition, associative memory, and tasks that measure other cognitive processes such as working memory, executive functions, and the growth in the individual's knowledge base across development as this related cognitive aspect is intertwined with memory development.  Our studies use extensive behavioral assessments, neuroimaging protocols looking at the structure and function of the brain, genetic information, and longitudinal designs to allow multidimensional characterization of memory development.

Examining neurophysiological features underlying memory encoding and retrieval in the developing brain with intracranial EEG (iEEG) recording

Examining the contributions of the Prefrontal Cortex (PFC) and Medial Temporal Lobes (MTL) to episodic memory development using functional MRI (fMRI)

The PFC integrates information from a wide range of cortical regions, including regions in the MTL and occipital lobe. Moreover, the PFC is considered the region with the most protracted structural and functional developmental profile. We are interested in how distinct regions within the PFC support developmental gains in memory. We use fMRI activations and are particularly interested in assessing how the connectivity between PFC and other regions varies across development.

We are working on differentiating the functional patterns along the anterior-posterior (also referred to as 'long') axis of the hippocampus using task-based fMRI studies with children and adults. Closely related to its structural development, we have shown that the hippocampus also shows differential functional development along its long anterior and posterior axis. Previous studies have found that the anterior and posterior MTL differ in many functional dimensions, with the anterior encoding more abstract, item-related, or verbal information, whereas the posterior encoding more detailed, context-related, or spatial information. We are especially interested in how anterior and posterior MTL differentially support the development of episodic memory with respect to these functional dimensions. 

Establishing the reliability of fMRI measures is an avenue of research we are rigorously pursuing and in future work we will establish a longitudinal study cross with test-retest reliability which will expand recent findings we published and allow even more rigorous interpretations of changes in task-based fMRI memory metrics.

Assessing variability in hippocampal structure across development

Assessing variability in regional hippocampal volume across development

We are interested in the structural and functional development of the medial temporal lobe (MTL). In particular, our research is focused on the hippocampus, a key region in the MTL that is essential for memory. The hippocampus shows anatomical and functional heterogeneity both with respect to its underlying subfields (subiculum cornu ammonis (CA) 1-3, and dentate gyrus), and its anterior/posterior axis. We aim to characterize this hippocampal regional heterogeneity in the context of brain and cognitive development. For example, we study how the variability in volume of certain hippocampal subfields, such as the dentate gyrus (the only place where neurogenesis continues in the adult brain), may be linked to age-related variability in certain aspects of memory. In an ongoing longitudinal study, we aim to assess change patterns in the hippocampal subfields volume and whether those measures can indicate different patterns of memory development.

The hippocampus. The word "hippocampus" means "seahorse" in Latin. The brain structure was so named because of its resemblance to the marine creature (on right). 

Our primary technique to study hippocampal regional volumetry incorporates manual demarcation on brain images with ultra-high in-plane resolution (0.4×0.4 mm²). We follow rigorous rules and protocols in our tracing and assure that prior to actually tracing, each tracer establishes high reliability in tracing the given region. We developed a protocol for the estimation of volumes of the hippocampal head, body, and tail (Daugherty et al., 2015), and we participate in large group efforts to develop harmonized protocols for hippocampal subfield segmentation (https://hippocampalsubfields.com/). Manual demarcation of Hc subfields Coronal image at the level of the hippocampal body of a single participant with 2-year follow-up, overlaid demarcations showing (from Homayouni et al., 2021).

The interaction of perception and memory

We study how brain regions involved in visual perception contribute to memory. Brain regions that support the perception of complex visual materials such as visual scenes show protracted development. We are interested in how these regions may be involved in children's memory performance. Using fMRI, we are investigating how scene-sensitive regions (e.g., parahippocampal place area [PPA]) and object-sensitive regions (e.g., lateral occipital cortex [LOC]) support memory formation. Using iEEG we are investigating the contributions of the occipital cortex to the memory of scenes and the interactions between visual cortices and the MTL during memory encoding and retrieval. 

In addition, with the use of novel behavioral paradigms, we assess the interaction between the development of perception and memory. In a current study, we show children pictures of many scenes and objects to remember, and later we test their memory performance. We manipulate factors such as the timing of the presentation and the similarity among the to-be-remembered objects to discern the interaction between visual perception and memory.

The interactions of memory and metamemory

Metamemory is the introspective knowledge or awareness of one's memory capabilities, mnemonic strategy use, and the processes involved in memory self-monitoring. Previous studies have shown that both the use of semantic chunking and memory recall performance increase with age. We are attempting to understand this concept further and determine how the relationship between strategy use and memory recall changes across development. Specifically, we are examining whether such strategy use improves recall similarly for children and adults.

We have been able to show that initial memory recall and the ability to learn through repetition both increase with age. Similarly, the use of semantic chunking in initial recall and the ability to increase that use throughout repeated learning both increase with age. This may account for why younger children have lower initial recall and are not able to gain from repetitions as much as older participants. We also found that more semantic chunking in initial recall was associated with better initial recall; however, it is still unclear how much this association is accounted for solely by age. We are investigating methods of measuring semantic chunking with this important developmental question in mind.

We are also interested in whether and how other metamemory components may play a role in memory development. In one project, we investigated the relationship between associative recognition memory and belief in the efficacy of mnemonic strategies. We found that people show increasingly stronger belief in the efficacy of deep encoding strategies from childhood to adulthood, which may account for the development of associative recognition memory during the same period. In another project, we investigated the relationship between the prediction of remembering the stimuli during the study phase and actual memory during the test phase. We found that adults are better than children in accurately predicting their memory performance. 

Additional Research Directions and Collaborations

Our lab established many collaborative projects. Below is a partial list of ongoing projects we participate in:

Lifespan Cognitive Neuroscience: Assessing Functional and Structural Brain Development from Childhood to Older adulthood

Enhancing Pediatric iEEG Research: Establishing a Consortium of Research Labs and Centers

Testing Novel Measures of Brain Structural Integrity Linked to Memory Development 

Testing Memory in Atypical Brain Development, including ongoing work with Epilepsy patients and Preterm Born Children

Educational Implications for Cognitive Neuroscience of Memory

In search of Proto-syntax in the Brain