I'm more and more convinced that low-dimensional manifolds in the brain are just an artifact of the experimental designs and analyses we use...
🧠📈 🧪
Dimensionality reduction may be the wrong approach to understanding neural representations. Our new paper shows that across human visual cortex, dimensionality is unbounded and scales with dataset size—we show this across nearly four orders of magnitude.
journals.plos.org/ploscompbiol...
For this paper, it’s worth considering that structure in brain activity need not be linear…
Sure, that's fair. But, do you think it's really just a low-D manifold curled up many times?
Why would you actually want a low-D manifold for most real-world tasks?
Low-d dynamics are useful - they are noise robust and easier to control.
BUT you also get a major benefit from curling up a low-D state manifold in a high-D embedding space: you can then linearly read out arbitrary functions of state!
Interesting, but I'm not sure I'm convinced... My intuition is that low-D dynamics, even when curled up, are probably not useful for representing information for arbitrary high-D tasks, no?
Like, if you're not letting yourself assume 1 task, can I get arbitrary states for any task this way?
Dec 15, 2025 15:38Some personal speculation: orienting geometry w.r.t. readout buys flexibility and helps composition from lower-D representation, manifolds can be labile and change between tasks/contexts based on inputs etc, a low-D surface could store arbitrarily many representations (see SueYeon's capacity work)
But ultimately I don't have much of "horse in the race" here about what is low-D, what is high-D. The brain probably uses a range of dimensionalities and strategies and some tasks are going to take a lot more dimensions than, say, limb movements. It's all fun to think about :)
Agreed with the point that manifolds are probably different between contexts… I guess the question is whether the manifolds are constrained by physical circuits (a la Langdon & Engel) or simply defined by tasks. I also don’t really have a horse in the race!
