
Neuroscientist. We aim to understd brain networks and brain wiring, using lasers & neuro AI. Prev: policy for @democracypolicy. Personal views. Not a lab acct.
Washington, DC
Joined May 2013
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Mark Histed retweeted
See also @HistedLab's wonderful thread for more details on the (hard) lessons in interpretability we learned in systems neuroscience: xitter.cf/HistedLab/status/21114…
I have a lot of respect for @nickcammarata and Goodfire, but I will add some thoughts from brains/neuroscience.
First, polysemanticity and distributed representations are ~widely~ seen in biological brains. (In some ways this is what I have spent my career on.) 1/
Mark Histed retweeted
Yes to all of this thread
I have a lot of respect for @nickcammarata and Goodfire, but I will add some thoughts from brains/neuroscience.
First, polysemanticity and distributed representations are ~widely~ seen in biological brains. (In some ways this is what I have spent my career on.) 1/
Mark Histed retweeted
The difference between industry PR and rigorous academic discussion. Worth a read.
This is outrageous framing. Quite frankly, given the current tensions around AI and mathematics, this kind of announcement does not help.
After the recent Buckmaster/OpenAI dispute over scientific credit and provenance, the last thing we need is more promotional PR language that blurs the history of a research problem.
Meta presents its work by asking: “Can AI contribute when a problem is genuinely open and without an existing solution path?”
Seriously?! For the ellipsoid-fitting example, this is misleading and insulting. There was an established research programme, substantial rigorous progress, and by the time of their announcement, publicly available proofs of the exact threshold.
Let us be specific:
- In 2023, Antoine Maillard and Dmitriy Kunisky gave a statistical-physics derivation of the conjectured transition at n/d² = 1/4, using the replica method. Their analysis also predicted the geometry of the solutions and suggested directions for rigorous proofs. This was not a proof, but it was a detailed and successful theoretical picture, not an absence of a path.
arxiv.org/abs/2310.01169
- Afonso Bandeira and Antoine Maillard then rigorously established the sharp threshold for approximate fitting, using methods inspired by the statistical physics of disordered systems, using actually spin glass mathematical technics. Their preprint appeared in 2023 and was published in the Electronic Journal of Probability in 2025. Their Gaussian-equivalence framework provided a foundation for further work (including many of mine!). At this point, the "exact" fitting and removing the spectral restriction were the outstanding gaps, but these are technical problems, it was not about not discovering the threshold from scratch. arxiv.org/abs/2310.05787
- On 10 August 2026, Theodor Misiakiewicz and Garrett Wen posted a proof of the exact Gaussian threshold, explicitly closing those two gaps.
arxiv.org/abs/2608.10184
- On 12 August, Sofia de la Cerda, Aaron Potechin, Madhur Tulsiani and Jeff Xu posted another proof, establishing both sides of the transition up to a vanishing multiplicative factor. arxiv.org/abs/2608.12415
- On 27 August, Frederic Koehler and Youngtak Sohn posted a broader universality theorem that includes the Gaussian threshold. arxiv.org/abs/2608.27372
These were not researchers merely “on the verge” of solving the problem. THE PROOFS WERE ALREADY PUBLIC. Meta's announcement comes in October, and Section 3 of their paper begins:
“We use the groundbreaking approximate-fitting theorem of Bandeira and Maillard…”
Dear META: Those are your words. This is not simply a reference in the bibliography: your feasibility proof explicitly starts from their theorem.
How is that consistent with advertising this example through the suggestion that there was “no existing solution path”?
Yes, your social post mentions independent solutions, and your paper and blog identify the August results and describe your work as independently developed. That does not answer the objection to the framing. A generic acknowledgement of parallel work does not make clear that the exact threshold already had publicly available proofs before this announcement.
An independently developed AI-assisted proof, released after other proofs, should be presented as exactly that. Readers should not have to reconstruct the chronology to understand what is, and is not, new.
A new proof can contain valuable ideas. But a new proof and a newly solved problem are not the same claim. Nor does a problem being open when a project begins mean it is still open when the marketing campaign launches.
You say the aim is to “empower researchers”? Nothing more “empowering” than seeing years of collective research turned into the backdrop for a cheap marketing stunt.
Correct the announcement! Give the scientific history the same prominence as the product. Give Antoine, Afonso, Theo and all the other researchers involved the public credit they deserve.
Mark Histed retweeted
What happened to LANL and LLL around the turn of the century that could have changed the culture dramatically?
Mark Histed retweeted
It's great to do math olympiads if that's ur thing. But there r many other ways to learn to work hard, push limits without burning out, keep cool under pressure, lose gracefully, team work, leadership etc. Kids shud pursue whatever avenues help unleash the best in them.
Mark Histed retweeted
If Scott Atlas thinks private entities are going to take on projects with basic science timelines and return schedules, I’ve got beachfront property to sell him in Phoenix.
Mark Histed retweeted
It's deeply depressing when big ARPA-style calls in your area look like they're going to be interesting but are so framed by a misunderstanding or oversimplification of the science that it's pretty clear they're going to waste money on bullshit vaportech and not actually help
Mark Histed retweeted
Thanks @beenwrekt for a beautiful tribute to Dmitri Bertsekas. I TA'ed for Bertsekas and Tsitsiklis's probabilistic systems course as an undergrad. I was 20 years old and younger than many of the grad students I was teaching so I was quite nervous on the inside. Bertsekas was so kind and he even told me I was one of his favorite TA's (I am sure he said that to many TAs). But that kindness I experienced from him at such a young age, when I was still unsure and forming my scientific self, stuck with me through so many years. Was very sad to hear of his passing.
My teacher and friend Dimitri Bertsekas passed away earlier this month. I wrote about his broad contributions to the field of numerical optimization and his deep impact on my writing and research. argmin.net/p/a-tribute-to-di…
Mark Histed retweeted
Many of America’s enormous scientific achievements have been built on the principle “that scientific judgement should not be supplanted by political pressures,” @HistedLab writes. “But that principle is under attack”: theatlantic.com/ideas/2026/0…
Mark Histed retweeted
Many of America’s enormous scientific achievements have been built on the principle “that scientific judgement should not be supplanted by political pressures,” @HistedLab writes. “But that principle is under attack”: theatlantic.com/ideas/2026/0…
Mark Histed retweeted
Yep. Check out our 2014 paper on this: papers.nips.cc/paper_files/p…
Local minima are rare in high dimensions because a strict local minimum has to curve upward in every direction, so all Hessian eigenvalues must be positive.
In a D-dimensional toy model where eigenvalue signs are independent, that’s a 2^(-D) event. In GOE-like random matrix models, positive definiteness is even rarer, roughly exp(-cD^2).
So as dimension grows, random critical points are much more likely to be saddles than minima. This is one reason high-dimensional optimization is often a saddle-escape problem, not a bad-local-minimum problem.
Wrote up some of the math here: grantstenger.com/local-minim…
Mark Histed retweeted
On efficient orgs:
“The antidote to a corrupted metric is usually direct contact w/ reality— interviews, frontline observations, case reviews, unscripted convos. Leaders who do this well build it into their routines structurally…” @pahlkadot
Yes. Accords with my experience.
Mark Histed retweeted
Excited to share our latest in @CurrentBiology (they who publish the coolest papers!)
Memories are encoded by sparse neuronal ensembles (engrams). But most evidence comes from "simple" associative learning tasks. What about more integrative memories like spatial navigation?
Presidentialist Governance is Incompatible with the American Science Superpower papers.ssrn.com/sol3/papers.… via @HistedLab et al
Mark Histed retweeted
100% this
Mark Histed retweeted
So excited to finally share this!
Linear probes often outperform SAEs, especially out-of-distribution (OOD). @thesubhashk @JoshAEngels et al showed this convincingly (arxiv.org/abs/2502.16681). This prompted @NeelNanda5 and others to de-emphasize SAE research. Empirically, fair enough. But we think the theoretical case for dictionary learning was dismissed too quickly.
@oneill_c previously showed SAEs can't do proper sparse coding (arxiv.org/abs/2411.13117). @shruti_joshi @vpacela and @isacama_phys took this further and showed how this leads to problems particularly in OOD settings. So the issue may not be with dictionary learning itself, but with the current tools.
Here's the core argument: if neural representations are in superposition, i.e. more features than dimensions encoded linearly (arxiv.org/abs/2503.01824), then linear probes fundamentally cannot be the answer.
This is a compressed sensing problem. There's a linear measurement (the representation) and a nonlinear inference procedure (like an SAE encoder) that recovers the higher-dimensional sparse signal. Linear algebra tells us error-free recovery is impossible if decoding is restricted to be linear. (but see this cool work if errors are acceptable arxiv.org/abs/2602.11246)
Check out our video: We have some neat demonstrations here. A linear decision boundary in 3D becomes nonlinear in 2D, even though all sparse combinations of latents remain distinguishable. Compressed sensing works: we can, in principle, recover the high-dimensional latent space where linear probes work and generalize OOD.
Where does this leave us? With finite data and millions of concepts, simpler methods may perform better for a while. But if we want interpretability and safety methods that work OOD, especially compositional generalization covering all possible jailbreaks and real-world failures, we'll have to build bottom up from the right theory.
@kennylpeng @thebasepoint @tegmark @yash_j_sharma @woog09 @livgorton @EkdeepL @thomas_fel_ @nsaphra
Shruti Joshi@_shruti_joshi_Apr 1Canada
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SAEs fail at OOD tasks. Why?
Features in superposition are linearly representable but not linearly accessible. Instead of discarding sparse coding, we embrace the geometry of superposition and use methods equipped to handle the nonlinearity it induces.
Mark Histed retweeted
Today I attended an interesting important talk by Lauren Williams on the “First Proof” project at Harvard CMSA. Mathematicians listed problems they had solved but not posted online, and invited AI companies to solve them, testing AI beyond internet-available answers. (1/3)
Mark Histed retweeted
There is no evidence that AI will supercharge the allocation decisions — the expert decision making that is the grant peer review process.
The biggest problem with grant peer review is low funding rates.
And AI’s limitations are exactly this-in areas where humans are expert.
Mark Histed retweeted
This must sound so awesome if you don’t understand the difference between million and billion






























