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neurosock

@neurosock.bsky.social
264 followers 19 following 696 posts

I make #neuro papers easy to understand. To make #Neuralink possible. #BrainChips recaps. Neuro PhD. AI🤖ML👾Data Sci 📊 Monkeys🐵Future🚀Cyberpunk⚡🦾🌌

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neurosock @neurosock.bsky.social · 13/10/2026
Thanks to you for reading Janel! It was very fun to make it. I am preparing a new one on thalamus. That paper is blowing my mind 🤯
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neurosock @neurosock.bsky.social · 11/10/2026
Correction: Christopher **Summerfield**
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neurosock @neurosock.bsky.social · 10/10/2026
By Christopher Summer and Kimberly Stachenfeld in Oxford, Columbia and DeepMind October 07, 2026 www.cell.com/neuron/full...
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neurosock @neurosock.bsky.social · 10/10/2026
To pursue extended goals, the PFC monitors performance and the value of cognitive control, thus preventing goal abandonment. #AI models struggle with #hallucinations because they lack this monitoring circuit--forcing #engineers to reinvent it as an agent "harness". #Neuroscience
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neurosock @neurosock.bsky.social · 05/10/2026
I guess I have a couple more neurons left from watching so much TV as a kid ... But not so many more 😬 ... I take that as a compliment ?? or do you mean something more profound ?
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neurosock @neurosock.bsky.social · 05/10/2026
Was thinking exactly the same ...
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neurosock @neurosock.bsky.social · 05/10/2026
If you like this, and think I should keep doing these posts, hit a like on the first post. It motivates me to spend 10-20 hours preparing each summary.
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neurosock @neurosock.bsky.social · 05/10/2026
Look at the architecture visualization yourself: neurocore.bio/explainers/...
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neurosock @neurosock.bsky.social · 05/10/2026
POYO: doi.org/10.48550/ar... NDT2: doi.org/10.1101/202...
biorxiv.org
Neural Data Transformer 2: Multi-context Pretraining for Neural Spiking Activity
The neural population spiking activity recorded by intracortical brain-computer interfaces (iBCIs) contain rich structure. Current models of such spiking activity are largely prepared for individual experimental contexts, restricting data volume to that collectable within a single session and limiting the effectiveness of deep neural networks (DNNs). The purported challenge in aggregating neural spiking data is the pervasiveness of context-dependent shifts in the neural data distributions. However, large scale unsupervised pretraining by nature spans heterogeneous data, and has proven to be a fundamental recipe for successful representation learning across deep learning. We thus develop Neural Data Transformer 2 (NDT2), a spatiotemporal Transformer for neural spiking activity, and demonstrate that pretraining can leverage motor BCI datasets that span sessions, subjects, and experimental tasks. NDT2 enables rapid adaptation to novel contexts in downstream decoding tasks and opens the pa
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neurosock @neurosock.bsky.social · 05/10/2026
Original post: neuralink.com/updates/pre...
neuralink.com
Pretraining on 50,000 Hours of Unlabeled Brain Data
How self-supervised encoders kept neural decoders working for weeks without recalibration and set an 11.32 BPS record.
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neurosock @neurosock.bsky.social · 05/10/2026
Disclaimers: 1) A simplification of a blog post and two papers. Many details are missing. 2) The diagrams are my reconstruction, with inferred parts marked. 3) I used AI to help understand the papers and build the diagram.
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neurosock @neurosock.bsky.social · 05/10/2026
A twist: POYO and NDT2 pitch pooling data across participants (offline wins). Neuralink says pooled models don't beat single-participant ones online yet, though transfer works. So pretraining on your own data is what seems to pay off first.
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neurosock @neurosock.bsky.social · 05/10/2026
Third, evidence from daily use: Six participants set personal bests, one hit a BCI record of 11.32 bits/s, smoothing and click post-processing became unnecessary, and some users went from 10 min of calibration a day to 10 a week. All reported in a blog post, so grain of salt.
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neurosock @neurosock.bsky.social · 05/10/2026
Second, deployment: POYO averages overlapping 1 sec windows, so it isn't a real-time loop. NDT2 was causal and had a closed-loop pilot, but as a transformer over a 2.5 sec window. which might explain Mamba, constant cost per step, state carried along.
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neurosock @neurosock.bsky.social · 05/10/2026
First, scale and setting: POYO used ~100 hours of monkey data. NDT2's authors call their pretraining "modestly scaled". This is 50,000 hours from chronic human implants during freeform daily use. The first participant alone has 9,000+ hours.
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neurosock @neurosock.bsky.social · 05/10/2026
Is the idea novel? Not at the level of ingredients. Unlabeled pretraining of spiking models was NDT2. Spike tokens and the Perceiver were POYO. If you only count the recipe, it's a recombination. The interesting parts are elsewhere.
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neurosock @neurosock.bsky.social · 05/10/2026
What does Neuralink "borrows" from these? POYO: spike tokens, channel embeddings, the Perceiver. NDT2: masked reconstruction with Poisson loss, small heads on a frozen encoder. The P9 to P2 transfer (99% of weights frozen) smells like POYO's unit identification.
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neurosock @neurosock.bsky.social · 05/10/2026
What is NDT2? A masked-autoencoder transformer on binned spikes (20 ms bins). Hide ~50% of the tokens, reconstruct their firing rates with a Poisson loss, then train small decoders on top. They tested this in closed-loop cursor pilot in one human participant.
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neurosock @neurosock.bsky.social · 05/10/2026
What is POYO? Each spike is a token (which unit + when). A Perceiver compresses them into latents, and a query asks "hand velocity at time t?". Trained with behavior labels. To reuse it on a new session: freeze everything, learn only new unit embeddings.
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neurosock @neurosock.bsky.social · 05/10/2026
Why using Mamba? The deployed decoder has to be fully causal with constant cost per step, which suits a state-space model. For training: show half the channels, predict the other half. The model has to learn the population state, not just autocorrelation.
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neurosock @neurosock.bsky.social · 05/10/2026
The other things are details. Why using a Perceiver? Spikes are sparse: a different number of events every moment. Each channel gets an embedding that only enters the model when it fires (POYO-style), and the Perceiver squeezes however many events into a fixed-size summary.
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neurosock @neurosock.bsky.social · 05/10/2026
These embeddings are rather stable. Which is unusual for neural signals. Here is an image from the blog:
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neurosock @neurosock.bsky.social · 05/10/2026
The encoder outputs a low dimensional representation of what the user wants (256-512 dims ???) and small decoders are trained on top for each modality: cursors, click, robot.
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neurosock @neurosock.bsky.social · 05/10/2026
The channel embeddings are the first step of the "Encoder" that can be pre-trained and also (likely) remains fixed. Instead of decoding raw spikes, a pretrained Encoder turns them into a stable embedding. To pre-train the Encoder, it is forced to predict masked spike channels.
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neurosock @neurosock.bsky.social · 05/10/2026
Every time a spike is detected, the word cat is added to a bag of words corresponding to the current time step. Of course "cat" is a bad example, but it is some kind of unique n-dim vector that, importantly, remains fixed, but is unique to each participant.
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neurosock @neurosock.bsky.social · 05/10/2026
Meanwhile 50,000 hours of freeform use just sat there ... My guess is that they use two types of embeddings: - Channel embeddings - Output embeddings The channel embeddings are fun: neural channels are treated like a specific word. E.g. ch17 is assigned the word "cat" and ...
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neurosock @neurosock.bsky.social · 05/10/2026
so, why do they need this? BCI decoders are trained per user and per feature, and neural signals drift. So users have to re-calibrate all the time, and that's super annoying: ~55 min a week on average, and the old labeled data gets thrown away.
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neurosock @neurosock.bsky.social · 05/10/2026
Interesting aspects appear, but first some caveats: This comes out of a long conversation between me and Opus, so take this as a grain of salt This architecture is one possible way the decoder works, built from the post, POYO, NDT2, and a lot of guessing.
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neurosock @neurosock.bsky.social · 05/10/2026
I reverse engineered Neuralink's new decoder arch. out of their blog post. As usual, they used the HARD work of other labs, and share nothing about the internals. Cortical activity is converted to bags of "words", producing a low-dimensional representation ... 🧵 #neuroskyence #compneuro #NeuroAI
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Reposted by neurosock
neurosock @neurosock.bsky.social · 01/10/2026
Mix. selectivity is everywhere in cortex: from vis. to PFC This paper relates to Cover's theorem but the typical explainer kind of sucks I'll try to explain how the theory relates to the paper, and the importance of "weird" neurons A🧵with my toy model and notes: #neuroskyence #compneuro #NeuroAI
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neurosock @neurosock.bsky.social · 01/10/2026
If you like this, and think I should keep doing these posts, hit a like on the first post. It motivates me to spend 10-20 hours preparing each summary.
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neurosock @neurosock.bsky.social · 01/10/2026
Disclaimers: 1) This is a simplification from a very complex paper. Many details likely omitted. 2) As any research, this study has to be further replicated. 3) I am not an author on this paper. I do this for fun and learning. 4) I used AI for the images. I wrote the text myself.
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neurosock @neurosock.bsky.social · 01/10/2026
I was just trying to understand better the theory. Link to the paper: doi.org/10.1038/s41...
nature.com
Rarely categorical, highly separable representations along the cortical hierarchy
Nature - Cortical circuits prioritize diversity over categorical structure, supporting a computational regime geared towards high-dimensional, highly separable neural representations.
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neurosock @neurosock.bsky.social · 01/10/2026
I am not saying this is how the brain exactly does it. This example is still quite artificial, and linearity of neurons can be discussed, and adjustment of bias can be debated too, and ... However it is a bit closer to reality than making a single neuron do math functions.
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neurosock @neurosock.bsky.social · 01/10/2026
In the case of NN: you can add more neurons. Also, in the case of neurons, having a single layer with lots of random neurons, and the ability to adjust the slope and bias helps carving the space.
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neurosock @neurosock.bsky.social · 01/10/2026
However, the more dimensions you have, the easier it would be to find the right cut planes (in the case of neurons, random neurons). The implementation makes the difference: on math you can add some helpful features.
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neurosock @neurosock.bsky.social · 01/10/2026
Cover's theorem is not directly about neurons but more about dimensions and geometry. What Cover's theorem says (at least how I understand it now), is that the more red dots you have, and the more complex that shape gets, the more extra dimensions you'll need.
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neurosock @neurosock.bsky.social · 01/10/2026
This problem can be of course be extended to more complicated geometries.
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neurosock @neurosock.bsky.social · 01/10/2026
In this hyper-cube it is easy to see how a linear surface can be formed. In 4D this corresponds to a 4D hyper-plane: a 3D cube that can be formed around the red circle. This can be done by a single readout neuron.
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neurosock @neurosock.bsky.social · 01/10/2026
Note that at this point its is still not possible to separate blue stars from red circles. It gets very interesting beyond 3 dimensions. A new dimension can be visualized as a tesseract. That one segregates only the stars.
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neurosock @neurosock.bsky.social · 01/10/2026
And another the diamonds. You'll notice the neural space gets higher dimensional: one dimension per new neuron. Each new dimension corresponds to a cut in input space.
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neurosock @neurosock.bsky.social · 01/10/2026
Another neuron can specialize on separating the squares:
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neurosock @neurosock.bsky.social · 01/10/2026
Having a neuron that can adjust its weight and bias you can find a threshold that separates the triangles. In neural space that segregates the triangles:
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neurosock @neurosock.bsky.social · 01/10/2026
The brain needs to use more neurons. And those neurons can only do simple things. Here is how you solve that with **artificial** yet simpler neurons.
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neurosock @neurosock.bsky.social · 01/10/2026
The typical explainer uses a feature that transforms the points with some math function (e.g. some convex curve) and then a plane can be easily found. But NNs cannot just create a magical neuron that applies x^2 + y^2 to its input. Here is the example from Wikipedia:
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neurosock @neurosock.bsky.social · 01/10/2026
We'll use a slightly harder problem to explain the way I see it. The problem of separating a set of red dots surrounded by blue dots. This requires at least three intermediate neurons depending on the shape of the cluster. We'll use 4.
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neurosock @neurosock.bsky.social · 01/10/2026
Cover's theorem is related to the above example in that the addition of more neurons to those intermediate layers makes it easier to solve complex problems in NN. Problems like the day and night issue.
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neurosock @neurosock.bsky.social · 01/10/2026
There is a parallel universe where brains can be high-dimensional and categorical but seems to be mathematically hard. I leave that to you to explore. That's the gist of the paper and you can stop reading here. But thinking about it got me into a Cover's theorem rabbit hole.
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neurosock @neurosock.bsky.social · 01/10/2026
There are some caveats: 1) Not all areas of the brain fit in there. Some sensory areas tend to be in the two low quadrants. Maybe in these areas, boring neurons are more useful. 2) As the picture shows, lots of weird neurons do not immediately imply no categories.
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neurosock @neurosock.bsky.social · 01/10/2026
The paper from Posani and co is very deep, and has many messages, but the simplest way to put it is this one: Most of the cortex is filled with non-categorical "weird neurons". If you look at Fig. 1b, most of the brain would fit on the top left quadrant of this picture:
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