Lightnews — Scholar-powered news

Guido Meijer

@guidomeijer.com

1.6K followers 580 following 140 posts

👨‍🔬 Neuroscientist at the Donders Institute in the Battaglia lab. 🧠 Previously: International Brain Laboratory Using Neuropixels and virtual-reality to understand how the brain creates internal models of the world. www.guidomeijer.com

Posts Media Videos Starter Packs

Pinned

Guido Meijer @guidomeijer.com · Aug 5

🚨Pre-print alert🚨

We stimulated serotonin with optogenetics while doing large-scale Neuropixel recordings across the mouse brain. We found strong widespread modulation of neural activity, but no effect on the choices of the mouse 🐭

How is this possible? Strap in! (1/9) 👇🧵

doi.org/10.1101/2025...

Serotonin drives choice-independent reconfiguration of distributed neural activity

Serotonin (5-HT) is a central neuromodulator which is implicated in, amongst other functions, cognitive flexibility. 5-HT is released from the dorsal raphe nucleus (DRN) throughout nearly the entire f...

doi.org

3 35 91

Guido Meijer @guidomeijer.com · 16h

I was doing the second-to-last recording of my project and was happily thinking to myself that I haven't broken a single Neuropixel in the entire two year project.

You can guess what happened next...

Now I have to install a new probe just for one final recording 🙃

Guido Meijer @guidomeijer.com · 3d

I love how they came up with all this random stuff but for this one area they were like "I really don't know, just put a question mark"

3 3 20

Guido Meijer @guidomeijer.com · 17d

Getting a hundred bucks would have been nice! We had to pay them twelve thousand bucks instead.

1 1

Guido Meijer @guidomeijer.com · 18d

When I told my dad I published in Nature he was like "wow, you must have made a lot of money with that"

1 16

Guido Meijer @guidomeijer.com · 26d

Of course, that makes complete sense 🙃

Guido Meijer @guidomeijer.com · 26d

I don't know why people say X is going down the drain, my last post got lovely replies like this one:

2 2

Reposted by Guido Meijer

International Brain Laboratory @intlbrainlab.bsky.social · 27d

Want to collaborate with the International Brain Laboratory on your own project? We have funding to work with groups anywhere in the world to do new large-scale projects and we are looking for new partners! Learn more and apply: www.internationalbrainlab.com/ibl-core-apply

1 14 24

Reposted by Guido Meijer

Emilie Macé @mace-lab.bsky.social · 27d

Thrilled to share that our work is now published in Science! ✨

We found a preference for visual objects in the mouse spatial navigation system where they dynamically refine head-direction coding. In short, objects boost our inner compass! 🧭

www.science.org/doi/10.1126/...

🧵1/

8 71 170

Reposted by Guido Meijer

Matteo Carandini @carandinilab.net · 29d

If you're into podcasts, here's a good one on the @intlbrainlab.bsky.social brainwide map, by @newscientist.com

www.newscientist.com/podcasts/fir...

1 9

Reposted by Guido Meijer

Ben Hayden @benhayden.bsky.social · Sep 4

Sad day for peope who still believe brain areas are the primary organizational units of function in the brain.

www.nature.com/articles/s41...

A brain-wide map of neural activity during complex behaviour - Nature

The International Brain Laboratory presents a brain-wide electrophysiological map obtained from pooling data from 12 laboratories that performed the same standardized perceptual decision-making task i...

www.nature.com

11 51 210

Reposted by Guido Meijer

Simons Foundation @simonsfoundation.org · Sep 3

The ‪@intlbrainlab.bsky.social published 2 papers today on their work to create a map of neural activity across the entire mouse brain. Learn more about the lab: https://www.simonsfoundation.org/2025/02/20/how-do-our-brains-make-decisions-the-international-brain-laboratory-is-closing-in-on-answers/

How Do Our Brains Make Decisions? The International Brain Laboratory Is Closing In on Answers

How Do Our Brains Make Decisions? The International Brain Laboratory Is Closing In on Answers on Simons Foundation

www.simonsfoundation.org

8 24

Reposted by Guido Meijer

New Scientist @newscientist.com · Sep 3

The first complete activity map of a mammalian brain has revealed unprecedented insights into how decisions are made – and may even hint at the roots of intuition.

First map of mammal brain activity may have shown intuition in action

Scientists have mapped the activity that takes place across a mouse's entire brain as it decides how to complete a task - and the results could explain the origin of our gut feelings

www.newscientist.com

10 23

Guido Meijer @guidomeijer.com · Sep 3

Extremely proud to have contributed to this monumental effort of recording the entire mouse brain, at cellular resolution, during complex behavior 🧠🐭

International Brain Laboratory @intlbrainlab.bsky.social · Sep 3

Two flagship papers from the International Brain Laboratory, now out in ‪@Nature.com‬:
🧠 Brain-wide map of neural activity during complex behaviour: doi.org/10.1038/s41586-025-09235-0
🧠 Brain-wide representations of prior information in mouse decision-making: doi.org/10.1038/s41586-025-09226-1 +

2 18

Guido Meijer @guidomeijer.com · Aug 29

PSA: don't buy duragel from Cambridge Neurotech, it's a scam! 🚨

They charge $200 (incl. shipping) for a 16 ml spout. But duragel is just DOWSIL 3-4680 (see paper below) of which you can buy a large container of 210 ml for only $110. That's 24 times cheaper! 💸

www.sciencedirect.com/science/arti...

Artificial dural sealant that allows multiple penetrations of implantable brain probes

This study reports extensive characterization of the silicone gel (3-4680, Dow Corning, Midland, MI), for potential use as an artificial dural sealant…

www.sciencedirect.com

2 19

Guido Meijer @guidomeijer.com · Aug 13

Duct tape and hope are literally the only two things holding my rig together

Digital Science @digital-science.com · Aug 13

🚨 NEW #FoSci post. "You don't build a mission on duct tape and hope."

Our VP of #ResearchIntegrity, Dr Leslie McIntosh @mcintold.bsky.social, reflects on almost a year of Forensic Scientometrics and its discussion of trust in science & research.

🔗 Read now: fosci.substack.com/p/beyond-duc...

Guido Meijer @guidomeijer.com · Aug 6

Don't feel like reading? Check out my talk!

www.youtube.com/watch?v=QIl6...

1 14

Guido Meijer @guidomeijer.com · Aug 5

Yes that's definitely a possibility! I would have loved to do pathway specific stimulation of amygdala and frontal cortex projecting DRN neurons (e.g. see www.cell.com/cell/fulltex... ). But, you know, time.

Guido Meijer @guidomeijer.com · Aug 5

This project is part of the @intlbrainlab.bsky.social, funded by @simonsfoundation.org and @wellcometrust.bsky.social. Big thanks to my PI Zachary Mainen (not on Bluesky) at the @champalimaudf.bsky.social, Lisbon, Portugal ☀️
(9/9)

1 1

Guido Meijer @guidomeijer.com · Aug 5

All these data are open-source! 🎉 There's neural data 🧠, video data from three cameras 🎥, wheel movement trajectories 🛞, you name it!

You can easily access the data through our API and start your own serotonin project, for instructions see:

github.com/guidomeijer/...

(8/9)

GitHub - guidomeijer/SerotoninStimulation

Contribute to guidomeijer/SerotoninStimulation development by creating an account on GitHub.

github.com

1 1 7

Guido Meijer @guidomeijer.com · Aug 5

This subspace is an extra dimension which allows serotonin to modulate information to create new, orthogonalized, representations of the environment. This can be used to relay information regarding internal state, or facilitate the rapid updating of representations during flexible behavior. (7/9)

2 1 9

Guido Meijer @guidomeijer.com · Aug 5

How is it possible that serotonin modulates neural activity across the brain but does not affect behavior? We found that the serotonergic modulation occurs in a subspace which is orthogonal to the choice axis. We call this the "neuromodulatory subspace". (6/9)

1 1 11

Guido Meijer @guidomeijer.com · Aug 5

We expected that serotonin stimulation would change how mice incorporate a prior in their decision making. However, in the steering wheel task of the International Brain Laboratory there was no effect of 5-HT stimulation whatsoever. 🤔 (5/9)

1 2

Guido Meijer @guidomeijer.com · Aug 5

On this website you can interactively explore our data and have a look at how serotonin modulates your favorite region!

atlas.internationalbrainlab.org?buckets=meij...

(4/9)

1 2

Guido Meijer @guidomeijer.com · Aug 5

We found widespread modulation of neural dynamics across all recorded brain regions. Single neurons were either excited or inhibited by 5-HT. Regions like the PAG, mPFC and OFC were excited by serotonin whereas the hippocampus was suppressed. Regions in the middle were more balanced. (3/9)

1 3

Guido Meijer @guidomeijer.com · Aug 5

These are all the Neuropixel insertions we made across the mouse brain while optogenetically stimulating serotonergic neurons in the dorsal raphe nucleus with a fiber (thick grey tube). We recorded ~7500 neurons in total across a large number of brain regions 🧠 (2/9)

1 5