Raphael Vallat

Welcome!

I am a French neuroscientist specialized in sleep and dreaming.

I obtained my PhD from the University of Lyon in December 2017. My doctoral project was conducted with Dr. Perrine Ruby and aimed at understanding the neurophysiological basis of dream recall (i.e. how and why we sometimes recall our dreams and sometimes forget them). I am currently working as a postdoctoral researcher in Pr. Matthew Walker's lab at the University of California, Berkeley. My project aims at studying the impact of sleep deprivation on brain function and (social) decision-making.

I also have a strong interest in statistics, machine-learning and signal processing. I am the (co)-founder of several open-source Python packages that are currently under active development: Pingouin (statistics), Visbrain (sleep staging), YASA (sleep microstructure analysis) and EntroPy (signal processing).

News

Introducing YASA: Yet Another Spindle Algorithm

January 2019

I have been recently trying to create a robust, fast, and data-agnostic sleep spindle detection algorithm. The result is named YASA (Yet Another Spindle Algorithm) and you can find it on GitHub. The algorithm behind YASA is a fast (and hopefully smart) implementation of the method described in Lacourse et al (2018).

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PhD thesis online

October 2018

I have decided to upload the full PDF (and LaTeX files) of my PhD thesis. It's a long read but (hopefully) an up-to-date review of what we - sleep and dream scientists - know and do not know about dreaming. In short, the goal of this thesis is to give some elements of answer to a question asked by Aristotle more than two thousand years ago:

We must also inquire what the dream is, and from what cause sleepers sometimes dream, and sometimes do not; or whether the truth is that sleepers always dream but do not always remember (their dream); and if this occurs, what its explanation is.

• Vallat R. (2017). Content and frequency of dream reports: psychological and neurophysiological correlates. PhD thesis, Lyon 1 University.

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The cerebral correlates of sleep inertia

September 2018

I am thrilled to announce that our article on sleep inertia is published in NeuroImage.

• Vallat R., Meunier D., Nicolas and Ruby P. (2018). Hard to wake up? The cerebral correlates of sleep inertia assessed using combined behavioral, EEG and fMRI measures. NeuroImage [PDF]

Ever felt groggy, sleepy, and disoriented when awakening from a long mid-afternoon nap?

In this article, we have investigated this phenomenom, called "sleep inertia", using a combination of behavioral tasks, resting-state fMRI scans and continuous EEG. We have measured the brain function of 34 participants before an afternoon nap, 5 minutes straight after awakening and 25 minutes after. Our results show that sleep-specific brain activity does not disappear immediately after we wake up but instead persists for several minutes, as illustrated by decreased cognitive performance, increased EEG delta power and disruption of brain functional networks (the two latter being typically observed during sleep). In addition, we have found that this sleep inertia progressively dissipates across the first half hour after awakening and that its severity and duration is related to the depth of sleep prior to awakening.

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Pingouin: a statistical package in Python

April 2018

I am very happy to introduce my new open-source Python package, called Pingouin. Pingouin is born out of a personal need to reduce and simplify the number of steps in my statistical analyses. Pingouin provides simple and easy-to-grasp statistical functions for computing ANOVA, post-hoc tests, robust correlations, Bayes factors and effect sizes. Pingouin is based on Pandas and therefore allows to leverage the power of this latter. Learn more on the documentation or check the code on GitHub.

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Post doctoral position at U.C Berkeley

November 2017

I am thrilled to announce that I will join Pr. Matthew Walker at U.C Berkeley (USA) for a two-years post-doctoral position starting February 2018.

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New papers out

October 2017

• Vallat R.*, Combrisson E.*, Eichenlaub J-B., O'Reilly C., Lajnef T., Guillot A., Jerbi K. and Ruby P. Sleep: an open-source python software for visualization, analysis and staging of sleep data. Frontiers in Neuroinformatics, 11. * Co-first authors

This paper describes an open-source software dedicated to sleep scoring and sleep analysis that I co-developed with my friend and fellow PhD student Etienne Combrisson. See below or check the documentation for a description of its main features.

• Vallat R., Chatard B., Blagrove M. and Ruby P. Characteristics of the memory sources of dreams: a new version of the content-matching paradigm to take mundane and remote memories into account Plos One, 12.

This paper describes a behavioral study in which we looked at the relationship between waking-life and dream content. We asked 40 participants to record their dreams during 7 consecutive days and write down every waking-life experiences that they thought was somehow related to the dream. Our results show that dreams mix up various and heterogenous waking-life experiences (old and recent ones, trivial and emotionally important) and suggest that dreaming plays a role in emotional regulation.

Academics

Link to my full curriculum vitae (pdf format - last updated April 2020)

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• Education

• Expertise

• Teaching

Publications

Please find below a list of publications (last updated April 2020)
PDF versions are provided for individual, noncommercial purposes only. These files may not be reposted without permission. Copyright and all rights therein resides with the respective copyright holders, as stated within each paper.

• Ben Simon*, Vallat*, Barnes and Walker (2020). Sleep Loss and the Socio-Emotional Brain. Trends In Cognitive Sciences. * Co-first authors
• Vallat and Ruby (2019). Is it a good idea to cultivate lucid dreaming? Frontiers in Psychology.
• Plailly, Villalba, Vallat, Nicolas, and Ruby (2019). Incorporation of fragmented visuo-olfactory episodic memory into dreams and its association with memory performance. Scientific Reports, 9, 15687.
• Combrisson, Vallat, ..., and Jerbi (2019). Visbrain: A multi-purpose GPU-accelerated open-source suite for multimodal brain data visualization. Frontiers in Neuroinformatics, 13, 14.
• Vallat (2018). Pingouin: statistics in Python. Journal of Open Source Software, 3(31), 1026.
• Vallat, Meunier, Nicolas, and Ruby (2018). Hard to wake up? The cerebral correlates of sleep inertia assessed using combined behavioral, EEG and fMRI measures. NeuroImage [PDF]
• Vallat, Eichenlaub, Nicolas, and Ruby (2018). Dream recall frequency is associated with medial prefrontal cortex white-matter density. Frontiers in Psychology, 9, 1856.
• Vallat, Eskinazi, Nicolas, and Ruby (2018). Sleep and dream habits in a sample of French college students who report no sleep disorders. Journal of Sleep Research, 27, e12659. [PDF]
• Vallat (2017). Content and frequency of dream reports: psychological and neurophysiological correlates. PhD thesis, Lyon 1 University.
• Combrisson*, Vallat*, ..., and Ruby (2017). Sleep: an open-source python software for visualization, analysis and staging of sleep data. Frontiers in Neuroinformatics, 11. * Co-first authors
• Vallat, Chatard, Blagrove, and Ruby (2017). Characteristics of the memory sources of dreams: a new version of the content-matching paradigm to take mundane and remote memories into account Plos One, 12.
• Vallat, ..., and Ruby (2017). Increased evoked potentials to arousing auditory stimuli during sleep: implication for the understanding of dream recall. Frontiers in Human Neuroscience, 11.

Media outreach

General sleep science

• The sad truth about sleep-tracking devices and apps @ New York Times



• Why do some people always remember their dreams, while others almost never do? @ Discover Magazine



• Vivid dreams and their role in waking life @ WHYY (NPR)

Sleep inertia study

Vallat et al., NeuroImage, 2018

• Simultaneous EEG and fMRI measure sleep ‘inertia’ @ PhysicsWorld.com



• Brain scans reveal why it takes so long to wake up in the morning @ Inverse.com

Software development

Please visit my GitHub repository for an exhaustive list of the projects/softwares that I am contributing to.

Guides

Please find below some tutorials regarding the analyses I specialize in.