Research
Unlocking developmental fMRI
Science can only be as precise and rich as its methods afford. In the case of infant research, it is hard to ask questions about the contents of the infant mind because infants have a limited behavioral repertoire. For instance, an infant’s memory for an object is often measured by showing them that object again alongside a novel object for comparison and testing how long they spend looking at each one. Although ubiquitous, this measure of memory is indirect and difficult to interpret. In the last 20 years, neuroimaging methods like electroencephalography (EEG) and functional near-infrared spectroscopy (fNIRS) have made strides in providing new measures of infant cognition. Yet, task-based fMRI has not made the same progress. Indeed, fMRI's value might be greater in infants than adults, given that there are so few options for assessing the mind in infants. Hence, in my research, I have developed methods for conducting fMRI with awake, behaving infants. As part of this effort, I have published a protocol for collecting large quantities of high-quality data from infants and released the data and software associated with this project.
Highlights:
Ellis, C. T., Skalaban, L. J., Yates, T. S., Bejjanki, V. R., Córdova, N. I., & Turk-Browne, N. B. (2020). Re-imagining fMRI for awake behaving infants. Nature Communications, 11, 4523. Paper, experiment_menu (display) code, infant_neuropipe_(analysis) code, Data
Ellis, C. T., & Turk-Browne, N. B. (2018) Infant fMRI: A Model System for Cognitive Neuroscience, Trends in Cognitive Sciences, 22 (5), 375-387. Paper
Yates, T. S., Ellis, C. T., Turk-Browne, N. B. (2021). The promise of awake behaving infant fMRI as a deep measure of cognition. Current Opinion in Behavioral Sciences. 40, 5-11. Paper
Perceptual complexity and its development
The world is abundantly complex, yet our visual system seamlessly and accurately determines what is in our environment. Dating back to William James, it has been assumed that this complexity is a hindrance that our visual system must overcome. In my research with adults, I showed that complexity could help perception by giving it a scaffolding upon which to incorporate incoming information. I have also pursued how the developing brain deals with complexity. I found that infants as young as five months have the hierarchical retinotopic organization of the mature adult visual system. This suggests that incoming visual information undergoes a cascade of transformations to extract features of differing complexity, even at a young age.
Highlights:
Ellis, C. T., Yates, T. S., Skalaban, L. J., Bejjanki, V. R., Arcaro, M. J., & Turk-Browne, N. B. (2021). Retinotopic organization of visual cortex in human infants. Neuron, 109, 1-11. Paper, Code, Data
Ellis, C. T., & Turk-Browne, N. B. (2019). Complexity can facilitate visual and auditory perception. Journal of Experimental Psychology: Human Perception and Performance, 45(9), 1271-1284. Paper, Data
The origins of attention
Until infants can walk or crawl, the only way for them to explore their world on their terms is with their attention. Infants look at objects that interest them, they look in locations where they expect interesting things to happen, and they look longer at locations where surprising things occurred. These capacities for attention are important, but our understanding of how they are controlled in the brain is limited. In particular, it is unclear whether the neural architecture of infant attention resembles the adult attention system. In my work, I showed that infants can robustly deploy attention and that this attention recruits similar, but not identical, neural systems in adults. In particular, we found evidence that frontal cortex is critical for supporting the reallocation of attention, providing evidence against the dogma that the frontal cortex is not functional or behaviorally-relevant in infancy. Additionally, the non-overlap in recruited brain regions between infants and adults hints at the possibility that attention in infancy is supported by different component processes than adult attention.
Highlights:
Ellis, C. T., Skalaban, L. J., Yates, T. S., & Turk-Browne. N. B. (2021). Attention recruits frontal cortex in human infants. Proceedings of the National Academia of Sciences, 118 (12). e2021474118. Paper, Code, Data
The development of learning and memory
Infancy is the time in our lives when we learn the most, including language, motor skills, and social relationships; yet, as adults, we remember none of the experiences that led to this learning. How is it possible that infants can learn without remembering? In adults, the hippocampus mediates learning by storing new information and slowly consolidating that information into cortex. However, how the infant brain mediates learning is less clear since infants appear to have limited memory of events and experiences, and the hippocampus has a protracted development into adolescence. In my research, I have investigated how the infant brain supports learning and memory. Statistical learning, the ability to extract regularities across episodes, is one type of learning I have focused on because it is thought to be foundational to learning during infancy (e.g., language acquisition). I showed that the infant hippocampus is involved in statistical learning, providing the first evidence that this region is functional in human infants as young as four months.
Highlights:
Ellis, C. T., Skalaban, L. J., Yates, T. S., Bejjanki, V. R., Córdova, N. I., & Turk-Browne, N. B. (2021). Evidence of hippocampal learning in human infants. Current Biology, 31, 1-7 Paper, Code, Data
Advanced fMRI methods
Although the initial years of fMRI research involved developing tools to assess where in the brain task-based modulations were observed, the last 15 years have seen an eruption in the number of tools available to ask how information is represented in the brain. I helped create and publicly distribute tutorials for several advanced fMRI methods, such as representational similarity analysis, searchlights, functional alignment, and real-time fMRI. The advances taught in these tutorials arose from integrating cognitive neuroscience with computer science, statistics, and mathematics. I have sought to combine these fields in novel ways to develop new advanced imaging methods in my research. For instance, I tested the usefulness of topological data analysis to assess neural representations that are hard to measure with standard tools. I also developed a tool that can take real fMRI data and recreate simulated data with equivalent noise properties and pre-specified signal, which can be used for testing the plausibility of experimental designs and neural mechanisms.
Highlights:
Ellis, C. T., Baldassano, C., Schapiro, A. C., Cai, M. B., Cohen, J. D. (2020). Facilitating open-science with realistic fMRI simulation: validation and application. PeerJ, 8, e8564. Paper, Code
Ellis, C. T., Lesnick, M., Henselman-Petrusek, G., Keller, B., & Cohen, J. D. (2019). Feasibility of topological data analysis for event-related fMRI, Network Neuroscience, 3 (3), 695-706. Paper, Code
Yates, T. S., Ellis, C. T., Turk-Browne, N. B. (2021). Emergence and organization of adult brain function throughout child development. NeuroImage, 226, 117606. Paper
Kumar, S., Ellis, C. T., O'Connell, T. P., Chun, M. M., Turk-Browne, N. B. (2020). Searching through functional space reveals distributed visual, auditory, and semantic coding in the human brain. PLoS Computational Biology. 16 (12), e1008457. Paper
Kumar, M., Ellis, C. T., Lu, Q., Zhang, H., Capotă, M., Wilke, T. L., Ramadge, P. J., Turk-Browne, N. B., & Norman, K. A. (2020). BrainIAK Tutorials: User-Friendly Learning Materials for Advanced fMRI Analysis. PLoS Computational Biology. 16 (1), e1007549. Paper, Code