iiinova — where your digital self keeps evolving

Guido Meijer @guidomeijer.com · 05/08/2026

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!

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Guido Meijer @guidomeijer.com · 21/07/2026

Computational modelling revealed that the cortical DOWN state is global. The visual cortex does not receive direct dorsal raphe input, but is still transitioned into a DOWN state. The 5-HT induced DOWN state is widespead enough that the visual cortex is pulled into it by the rest of the brain.

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Guido Meijer @guidomeijer.com · 21/07/2026

Looking at the spike rasters across the entire probe we saw that 5-HT stimulation resulted in a DOWN state. To quantify this effect we fit a two-state HMM and found 5-HT induced DOWN states everywhere except the midbrain.

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Guido Meijer @guidomeijer.com · 21/07/2026

To answer these questions we did large-scale Neuropixel recordings across the anesthetized mouse forebrain while optogenetically stimulating dorsal raphe serotonergic neurons. We found that spiking activity across the brain was suppressed by serotonin stimulation.

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Guido Meijer @guidomeijer.com · 07/07/2026

Thanks to all who visited my poster for your interest and lively discussions 😃

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Guido Meijer @guidomeijer.com · 15/05/2026

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

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Guido Meijer @guidomeijer.com · 07/05/2026

Select a receptor subtype in the dropdown menu on the left ("Select a feature"). You can scroll through the views with the sliders underneath. You can also scale the colormap by going to "Control Panel" on the top right and changing the sliders sliders underneath "colormap range".

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Guido Meijer @guidomeijer.com · 05/05/2026

Then there is the issue of mass surveillance around the town. When something goes wrong, an AI system knows exactly what is happening and where. Even when nobody calls them. This is only possible through ubiquitous camera coverage with facial recognition software, these people have no privacy!

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Guido Meijer @guidomeijer.com · 05/05/2026

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 🧵

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Guido Meijer @guidomeijer.com · 11/11/2025

The Power Pixels pipeline just keeps getting better! The latest update comes with: - OpenEphys support - AP_Histology support - automatic high-frequency noise reduction - NWB format export option - zarr compression of raw data And, most importantly: a cool new logo! github.com/NeuroNetMem/...

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Guido Meijer @guidomeijer.com · 16/10/2025

A note about colors 🌈 Imagine you made eight figures and your PI asks you to change the color of an element you've consistently plotted green into orange. If you define your colors in the plotting function you only have to change it there and rerun the plotting scripts, this save a lot of time!

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Guido Meijer @guidomeijer.com · 16/10/2025

The font size of each plot element can be easily set with seaborn. Write a function like this that sets the font size and any other style element you like to have in all your plots and the function each time before plotting (link to the code in the last post).

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Guido Meijer @guidomeijer.com · 16/10/2025

Want to make publication-ready figures come straight from Python without having to do any manual editing? Are you fed up with axes labels being unreadable during your presentations? Follow this short tutorial including code examples! 👇🧵

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Guido Meijer @guidomeijer.com · 05/10/2025

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"

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Guido Meijer @guidomeijer.com · 12/09/2025

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

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Guido Meijer @guidomeijer.com · 05/08/2025

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)

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Guido Meijer @guidomeijer.com · 05/08/2025

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)

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Guido Meijer @guidomeijer.com · 05/08/2025

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)

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Guido Meijer @guidomeijer.com · 05/08/2025

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)

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Guido Meijer @guidomeijer.com · 05/08/2025

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)

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Guido Meijer @guidomeijer.com · 05/08/2025

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)

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Guido Meijer @guidomeijer.com · 09/04/2025

The PhD students started writing motivational quotes on the whiteboard

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Guido Meijer @guidomeijer.com · 11/01/2025

In my spare time I'm a singer-songwriter and just recorded my first couple of songs!

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Guido Meijer @guidomeijer.com · 07/01/2025

People who are still posting science content on X:

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Guido Meijer @guidomeijer.com · 15/11/2024

Yesterday I made a screenshot of my recording because it looked so nice, forgot about it, and then freaked out because I thought SpikeGLX had frozen 🫠

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Guido Meijer @guidomeijer.com · 13/11/2024

It includes pre-processing, spike sorting, neuron-level quality control metrics (IBL & BombCell), synchronization between multiple probes, compression of raw data, probe tracing (Universal Probe Finder) and ephys-to-histology alignment.

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Guido Meijer @guidomeijer.com · 12/11/2024

Starter packs are great and all but don't miss out on the Spotify playlist I made for all my fellow postdocs! Link 👉 open.spotify.com/playlist/2M2...

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Guido Meijer @guidomeijer.com · 07/11/2024

Absolutely love this paper! The subdivision of higher visual cortex in mice into a bunch of distinct areas (LM, AL, PM, etc.) is wrong, it's all just V2. Makes much more sense to me! www.biorxiv.org/content/10.1...

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Guido Meijer @guidomeijer.com · 03/11/2023

We're happy to share the extension of the ZETA-test into a full-fledged statistical family. 📈👨‍👩‍👧‍👦 Now you can also include more cells in your GCaMP data, and perform two-sample comparisons, all binning-free! With Jorrit Montijn and Alexander Heimel. www.biorxiv.org/content/10.1... #neuroscience

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Guido Meijer @guidomeijer.com · 11/07/2023

Are you on a budget? The repurposed hard drive method only has to cost 15 bucks! If you have an old hard drive laying around and your rig already has a stereoscope and micromanipulator you just need this: www.thorlabs.com/thorproduct.cfm?pa…

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