About

Professor Emily Stephen is an Assistant Professor in the Department of Mathematics & Statistics at Boston University. She is a member of the Probability and Statistics research group. For more information about Professor Stephen, please see her personal webpage.

Research topics

• Computer Science
• Neuroscience
• Physics
• Machine Learning
• Artificial Intelligence
• Biology
• Algorithm
• Psychology
• Mathematics
• Medicine
• Anesthesia
• Statistics
• Biological system
• Telecommunications
• Acoustics

Selected publications

• Propofol disrupts alpha dynamics in functionally distinct thalamocortical networks during loss of consciousness

  Proceedings of the National Academy of Sciences · 2023 · 52 citations

  • Neuroscience
  • Psychology
  • Biology

  During propofol-induced general anesthesia, alpha rhythms measured using electroencephalography undergo a striking shift from posterior to anterior, termed anteriorization, where the ubiquitous waking alpha is lost and a frontal alpha emerges. The functional significance of alpha anteriorization and the precise brain regions contributing to the phenomenon are a mystery. While posterior alpha is thought to be generated by thalamocortical circuits connecting nuclei of the sensory thalamus with their cortical partners, the thalamic origins of the propofol-induced alpha remain poorly understood. Here, we used human intracranial recordings to identify regions in sensory cortices where propofol attenuates a coherent alpha network, distinct from those in the frontal cortex where it amplifies coherent alpha and beta activities. We then performed diffusion tractography between these identified regions and individual thalamic nuclei to show that the opposing dynamics of anteriorization occur within two distinct thalamocortical networks. We found that propofol disrupted a posterior alpha network structurally connected with nuclei in the sensory and sensory associational regions of the thalamus. At the same time, propofol induced a coherent alpha oscillation within prefrontal cortical areas that were connected with thalamic nuclei involved in cognition, such as the mediodorsal nucleus. The cortical and thalamic anatomy involved, as well as their known functional roles, suggests multiple means by which propofol dismantles sensory and cognitive processes to achieve loss of consciousness.

  DOI

• State space methods for phase amplitude coupling analysis

  Scientific Reports · 2022 · 29 citations

  • Computer Science
  • Computer Science
  • Artificial Intelligence

  Phase amplitude coupling (PAC) is thought to play a fundamental role in the dynamic coordination of brain circuits and systems. There are however growing concerns that existing methods for PAC analysis are prone to error and misinterpretation. Improper frequency band selection can render true PAC undetectable, while non-linearities or abrupt changes in the signal can produce spurious PAC. Current methods require large amounts of data and lack formal statistical inference tools. We describe here a novel approach for PAC analysis that substantially addresses these problems. We use a state space model to estimate the component oscillations, avoiding problems with frequency band selection, nonlinearities, and sharp signal transitions. We represent cross-frequency coupling in parametric and time-varying forms to further improve statistical efficiency and estimate the posterior distribution of the coupling parameters to derive their credible intervals. We demonstrate the method using simulated data, rat local field potentials (LFP) data, and human EEG data.

  DOI

• Broadband slow-wave modulation in posterior and anterior cortex tracks distinct states of propofol-induced unconsciousness

  Scientific Reports · 2020 · 28 citations

  1st authorCorresponding
  • Computer Science
  • Neuroscience
  • Medicine

  A controversy has developed in recent years over the roles of frontal and posterior cortices in mediating consciousness and unconsciousness. Disruption of posterior cortex during sleep appears to suppress the contents of dreaming, yet activation of frontal cortex appears necessary for perception and can reverse unconsciousness under anesthesia. We used anesthesia to study how regional cortical disruption, mediated by slow wave modulation of broadband activity, changes during unconsciousness in humans. We found that broadband slow-wave modulation enveloped posterior cortex when subjects initially became unconscious, but later encompassed both frontal and posterior cortex when subjects were more deeply anesthetized and likely unarousable. Our results suggest that unconsciousness under anesthesia comprises several distinct shifts in brain state that disrupt the contents of consciousness distinct from arousal and awareness of those contents.

  DOI

Frequent coauthors

• Emery N. Brown

  Massachusetts Institute of Technology

  33 shared

• Yulia Oganian

  Bernstein Center for Computational Neuroscience Tübingen

  18 shared

• Yuanning Li

  ShanghaiTech University

  15 shared

• Patrick L. Purdon

  Stanford University

  15 shared

• Sean L. Metzger

  University of California, San Francisco

  12 shared

• Edward F. Chang

  Neurological Surgery

  12 shared

• David Schreier

  Center for Neuro-Oncology

  7 shared

• Robert A. Peterfreund

  Massachusetts General Hospital

  6 shared

Education

• Ph.D., Computational Neuroscience

  Boston University

  2015

• Sc.B., Cognitive Neuroscience

  Brown University

  2007

Similar researchers at Boston University

• Alexa S. Beiserh-188
• David Boash-156
• Benjamin Sovacoolh-143
• Kathryn L. Lunettah-132
• Ranga Mynenih-130