Guido Meijer
@guidomeijer.com
👨🔬 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
🧠 Previously: International Brain Laboratory
Using Neuropixels and virtual-reality to understand how the brain creates internal models of the world.
www.guidomeijer.com
Pinned
Guido Meijer
@guidomeijer.com
· Aug 5
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
🚨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...
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...
Distributing grants through a lottery has its advantages but I'm afraid it will result in even more AI generated grant applications. A lottery is a good idea but it has to be taken one step further to really work: no more grant proposals at all anymore.
www.thetransmitter.org/funding/gran...
www.thetransmitter.org/funding/gran...
How about adding an element of chance to grant review?
A process that uses a lottery system saves time and accepts that, above a quality threshold, luck has always played a part in science funding.
www.thetransmitter.org
September 25, 2026 at 1:14 PM
Distributing grants through a lottery has its advantages but I'm afraid it will result in even more AI generated grant applications. A lottery is a good idea but it has to be taken one step further to really work: no more grant proposals at all anymore.
www.thetransmitter.org/funding/gran...
www.thetransmitter.org/funding/gran...
Let me tell you, teaching a course to first year undergrads is a sure-fire way of making you feel really, really old.
September 16, 2026 at 8:51 AM
Let me tell you, teaching a course to first year undergrads is a sure-fire way of making you feel really, really old.
It was great to see the RIKEN institute in Japan and give a talk there. Thanks to Muhang Li and @tommchugh.bsky.social for inviting me!
August 5, 2026 at 5:40 AM
It was great to see the RIKEN institute in Japan and give a talk there. Thanks to Muhang Li and @tommchugh.bsky.social for inviting me!
If you're attending the NEURO2026 conference in Kobe, Japan ⛩️ don't miss our symposium on Sunday morning about the latest from the IBL @intlbrainlab.bsky.social. My talk on how neuromodulators shape decision-making starts at 09:55 🧠
July 31, 2026 at 9:13 AM
If you're attending the NEURO2026 conference in Kobe, Japan ⛩️ don't miss our symposium on Sunday morning about the latest from the IBL @intlbrainlab.bsky.social. My talk on how neuromodulators shape decision-making starts at 09:55 🧠
I am happy to announce my very first senior author paper! Serotonin is known to abolish UP-DOWN state dynamics, which occur during sleep and anesthesia. There are several outstanding questions: What happens at short latencies? How widespread across the brain is it? 🧠
www.biorxiv.org/content/10.6...
www.biorxiv.org/content/10.6...
Serotonin induces DOWN states across the anesthetized mouse forebrain
Serotonergic neurons in the dorsal raphe nucleus (DRN) project extensively throughout the forebrain, yet their influence on global network states remains controversial. Serotonin is implicated in regu...
www.biorxiv.org
July 21, 2026 at 9:15 AM
I am happy to announce my very first senior author paper! Serotonin is known to abolish UP-DOWN state dynamics, which occur during sleep and anesthesia. There are several outstanding questions: What happens at short latencies? How widespread across the brain is it? 🧠
www.biorxiv.org/content/10.6...
www.biorxiv.org/content/10.6...
Now that my daughter can say a few words I feel like being a servant to a neanderthaler.
I'm constantly being shouted at "food!", "give!", "yes good, more more!"
I'm constantly being shouted at "food!", "give!", "yes good, more more!"
July 16, 2026 at 7:54 AM
Now that my daughter can say a few words I feel like being a servant to a neanderthaler.
I'm constantly being shouted at "food!", "give!", "yes good, more more!"
I'm constantly being shouted at "food!", "give!", "yes good, more more!"
I wonder which layer of hell Dante reserved for the developers of the FENS app
July 10, 2026 at 6:19 AM
I wonder which layer of hell Dante reserved for the developers of the FENS app
Thanks to all who visited my poster for your interest and lively discussions 😃
July 7, 2026 at 3:13 PM
Thanks to all who visited my poster for your interest and lively discussions 😃
I'm on my way to Barcelona for #FENS2026! 🌞🧠Come see my poster tomorrow morning:
PS01-07AM-292 - DYNAMIC UPDATING OF REWARD PREDICTIONS BY THE PARA-HIPPOCAMPAL NETWORK
I did simultaneous Neuropixel recordings in CA1 and 5 cortical regions to find out how the brain switches between cognitive maps 🗺️
PS01-07AM-292 - DYNAMIC UPDATING OF REWARD PREDICTIONS BY THE PARA-HIPPOCAMPAL NETWORK
I did simultaneous Neuropixel recordings in CA1 and 5 cortical regions to find out how the brain switches between cognitive maps 🗺️
July 6, 2026 at 9:00 AM
I'm on my way to Barcelona for #FENS2026! 🌞🧠Come see my poster tomorrow morning:
PS01-07AM-292 - DYNAMIC UPDATING OF REWARD PREDICTIONS BY THE PARA-HIPPOCAMPAL NETWORK
I did simultaneous Neuropixel recordings in CA1 and 5 cortical regions to find out how the brain switches between cognitive maps 🗺️
PS01-07AM-292 - DYNAMIC UPDATING OF REWARD PREDICTIONS BY THE PARA-HIPPOCAMPAL NETWORK
I did simultaneous Neuropixel recordings in CA1 and 5 cortical regions to find out how the brain switches between cognitive maps 🗺️
Reposted by Guido Meijer
Meet SpudCell, a synthetic cell made from lifeless ingredients that feeds, grows, divides, and experiences selection. If it doesn't have all the hallmarks of life, it has a lot! Here's my story. Gift link: nyti.ms/4vCbTih
July 1, 2026 at 4:30 PM
Meet SpudCell, a synthetic cell made from lifeless ingredients that feeds, grows, divides, and experiences selection. If it doesn't have all the hallmarks of life, it has a lot! Here's my story. Gift link: nyti.ms/4vCbTih
Idea for an app!💡 World Cup football matches are often in the middle of the night for us Europeans; the Netherlands is playing at 3AM 💤 I want an app that wakes me at 5:30AM to see the penalty shoot outs, but only if there are any. Can someone who doesn't have a 2 year old develop this? Thanks! 🙏🏻
June 28, 2026 at 10:02 AM
Idea for an app!💡 World Cup football matches are often in the middle of the night for us Europeans; the Netherlands is playing at 3AM 💤 I want an app that wakes me at 5:30AM to see the penalty shoot outs, but only if there are any. Can someone who doesn't have a 2 year old develop this? Thanks! 🙏🏻
I wonder how many unnecessary figure panels have been made just to make the entire figure nice and rectangular.
June 12, 2026 at 9:39 AM
I wonder how many unnecessary figure panels have been made just to make the entire figure nice and rectangular.
Want your mice to learn your task faster? 🐭 According to this paper giving a huge reward (10x typical size) in a subset of trials strongly shortens training times:
www.science.org/doi/10.1126/...
www.science.org/doi/10.1126/...
Reward magnitude determines reinforcement learning efficiency
Standard animal learning studies minimize individual reward magnitudes to maximize the repetitions of reinforced behaviors. We investigated how reward magnitude influences initial learning across five...
www.science.org
June 9, 2026 at 6:56 AM
Want your mice to learn your task faster? 🐭 According to this paper giving a huge reward (10x typical size) in a subset of trials strongly shortens training times:
www.science.org/doi/10.1126/...
www.science.org/doi/10.1126/...
Reposted by Guido Meijer
Introducing the International Brain Lab AI Agent: a tool to help researchers analyze neural activity from across the mouse brain, using AI coding agents.
Please try it! We would love your feedback.
github.com/int-brain-la...
Please try it! We would love your feedback.
github.com/int-brain-la...
May 21, 2026 at 6:32 PM
Introducing the International Brain Lab AI Agent: a tool to help researchers analyze neural activity from across the mouse brain, using AI coding agents.
Please try it! We would love your feedback.
github.com/int-brain-la...
Please try it! We would love your feedback.
github.com/int-brain-la...
zetapy v4.0 is live! Due to various optimizations of the code it now runs 4x faster⚡Upgrade now and get your significant neurons in no time!
pip install zetapy==4.0
pip install zetapy==4.0
May 15, 2026 at 12:24 PM
zetapy v4.0 is live! Due to various optimizations of the code it now runs 4x faster⚡Upgrade now and get your significant neurons in no time!
pip install zetapy==4.0
pip install zetapy==4.0
Reposted by Guido Meijer
This website shows you what your browser is leaking about you. sinceyouarrived.world/taken
taken.
A web page that tells you what your browser gave away the moment you arrived. No login, no form, no permission. Most pages do this. None of them tell you.
sinceyouarrived.world
May 9, 2026 at 1:49 AM
This website shows you what your browser is leaking about you. sinceyouarrived.world/taken
Are you interested in serotonin receptors? I made a website which visualizes the expression of different 5-HT receptors! Data from the Allen Brain Atlas (@alleninstitute.org) website by the IBL Brain Viewer (@intlbrainlab.bsky.social).
atlas.internationalbrainlab.org?buckets=meij...
Instructions 👇
atlas.internationalbrainlab.org?buckets=meij...
Instructions 👇
IBL Brain Atlas
atlas.internationalbrainlab.org
May 7, 2026 at 8:53 AM
Are you interested in serotonin receptors? I made a website which visualizes the expression of different 5-HT receptors! Data from the Allen Brain Atlas (@alleninstitute.org) website by the IBL Brain Viewer (@intlbrainlab.bsky.social).
atlas.internationalbrainlab.org?buckets=meij...
Instructions 👇
atlas.internationalbrainlab.org?buckets=meij...
Instructions 👇
I've been watching Fireman Sam with my daughter (the new animated version) and I must say I'm deeply worried for the residents of Pontypandy, the small Welch village with a population of apparently 10 people. A thread 🧵
May 5, 2026 at 12:11 PM
I've been watching Fireman Sam with my daughter (the new animated version) and I must say I'm deeply worried for the residents of Pontypandy, the small Welch village with a population of apparently 10 people. A thread 🧵
I'm very happy that fairness and reason has prevailed and the ERC has backtracked on this. Thanks to everyone who signed the open letter to the ERC for making this happen 🙏🏻
www.thetransmitter.org/policy/europ...
www.thetransmitter.org/policy/europ...
May 5, 2026 at 10:25 AM
I'm very happy that fairness and reason has prevailed and the ERC has backtracked on this. Thanks to everyone who signed the open letter to the ERC for making this happen 🙏🏻
www.thetransmitter.org/policy/europ...
www.thetransmitter.org/policy/europ...
Reposted by Guido Meijer
So I (well Claude mostly) made a @julialang.org port of the ZETA test originally developped by Jorrit Montijn (published here: elifesciences.org/articles/71969). The port is faithful to zetapy (Python version by @guidomeijer.com and @alexanderheimel.bsky.social).
Enjoy
github.com/PierreLeMerr...
Enjoy
github.com/PierreLeMerr...
GitHub - PierreLeMerre/ZetaJu
Contribute to PierreLeMerre/ZetaJu development by creating an account on GitHub.
github.com
May 1, 2026 at 10:01 AM
So I (well Claude mostly) made a @julialang.org port of the ZETA test originally developped by Jorrit Montijn (published here: elifesciences.org/articles/71969). The port is faithful to zetapy (Python version by @guidomeijer.com and @alexanderheimel.bsky.social).
Enjoy
github.com/PierreLeMerr...
Enjoy
github.com/PierreLeMerr...
Reposted by Guido Meijer
🧠Introducing OmniMouse: One of the largest datasets in neuroscience along with a systematic study of scaling properties of brain models
Co-led by 🤩 K. Willeke, @pollytur.bsky.social and @alexrgil14.bsky.social
Models trained on up to 3M neurons, >150B tokens
Co-led by 🤩 K. Willeke, @pollytur.bsky.social and @alexrgil14.bsky.social
Models trained on up to 3M neurons, >150B tokens
April 24, 2026 at 7:41 PM
🧠Introducing OmniMouse: One of the largest datasets in neuroscience along with a systematic study of scaling properties of brain models
Co-led by 🤩 K. Willeke, @pollytur.bsky.social and @alexrgil14.bsky.social
Models trained on up to 3M neurons, >150B tokens
Co-led by 🤩 K. Willeke, @pollytur.bsky.social and @alexrgil14.bsky.social
Models trained on up to 3M neurons, >150B tokens
Reposted by Guido Meijer
Job alert! We are seeking a rodent in vivo electrophysiologist to work on coordination between anterior thalamus and hippocampus in rats using Neuropixels. Beautiful Scotland, leading university (Glasgow) and vibrant intellectual setting. Post is 23 months but hopefully extensible. Details here 👇
April 21, 2026 at 9:49 AM
Job alert! We are seeking a rodent in vivo electrophysiologist to work on coordination between anterior thalamus and hippocampus in rats using Neuropixels. Beautiful Scotland, leading university (Glasgow) and vibrant intellectual setting. Post is 23 months but hopefully extensible. Details here 👇
Reposted by Guido Meijer
Do you record spikes in vivo? Here are two recently recommended preprints on toolboxes for extracellular electrophysiology:
-MLIB doi.org/10.1101/2025... by Maik Stüttgen.
-Power Pixels doi.org/10.1101/2025... by @guidomeijer.com and @battaglialab.bsky.social.
-MLIB doi.org/10.1101/2025... by Maik Stüttgen.
-Power Pixels doi.org/10.1101/2025... by @guidomeijer.com and @battaglialab.bsky.social.
doi.org
April 18, 2026 at 8:03 AM
Do you record spikes in vivo? Here are two recently recommended preprints on toolboxes for extracellular electrophysiology:
-MLIB doi.org/10.1101/2025... by Maik Stüttgen.
-Power Pixels doi.org/10.1101/2025... by @guidomeijer.com and @battaglialab.bsky.social.
-MLIB doi.org/10.1101/2025... by Maik Stüttgen.
-Power Pixels doi.org/10.1101/2025... by @guidomeijer.com and @battaglialab.bsky.social.
The ERC is changing the rules retroactively!
A "B" grade now carries a 2-year timeout instead of 1, even for those who submitted under the old rules. Researchers (incl me) make massive career decisions based on these timelines, you can't change them after the fact 😵💫
erc.europa.eu/news-events/...
A "B" grade now carries a 2-year timeout instead of 1, even for those who submitted under the old rules. Researchers (incl me) make massive career decisions based on these timelines, you can't change them after the fact 😵💫
erc.europa.eu/news-events/...
ERC President explains stricter application measures amid rising demand for funding
The text of an open letter sent by ERC President Maria Leptin to ERC panel members, grantees and other stakeholders on 16 April 2026.
erc.europa.eu
April 17, 2026 at 12:20 PM
The ERC is changing the rules retroactively!
A "B" grade now carries a 2-year timeout instead of 1, even for those who submitted under the old rules. Researchers (incl me) make massive career decisions based on these timelines, you can't change them after the fact 😵💫
erc.europa.eu/news-events/...
A "B" grade now carries a 2-year timeout instead of 1, even for those who submitted under the old rules. Researchers (incl me) make massive career decisions based on these timelines, you can't change them after the fact 😵💫
erc.europa.eu/news-events/...
The Power Pixels ⚡ pipeline is out now in Peer Community Journal!
Are you doing Neuropixel recordings but don't have a pre-processing pipeline yet? Check out this end-to-end pipeline designed to simplify preprocessing of Neuropixel recordings 🧠
peercommunityjournal.org/articles/10....
Are you doing Neuropixel recordings but don't have a pre-processing pipeline yet? Check out this end-to-end pipeline designed to simplify preprocessing of Neuropixel recordings 🧠
peercommunityjournal.org/articles/10....
Power Pixels: a turnkey pipeline for processing of Neuropixel recordings
peercommunityjournal.org
February 26, 2026 at 8:03 AM
The Power Pixels ⚡ pipeline is out now in Peer Community Journal!
Are you doing Neuropixel recordings but don't have a pre-processing pipeline yet? Check out this end-to-end pipeline designed to simplify preprocessing of Neuropixel recordings 🧠
peercommunityjournal.org/articles/10....
Are you doing Neuropixel recordings but don't have a pre-processing pipeline yet? Check out this end-to-end pipeline designed to simplify preprocessing of Neuropixel recordings 🧠
peercommunityjournal.org/articles/10....