Colin Bredenberg

Representational drift without synaptic plasticity Neural computations support stable behavior despite relying on many dynamically changing biological processes. One such process is representational drift (RD), in which neurons' responses change over ...

When neurons change, but behavior doesn’t: Excitability changes driving representational drift

New preprint of work with Christian Machens: www.biorxiv.org/content/10.1...

Great review! Section 4.2 in particular looks very consistent with our 'oneirogen hypothesis' model (elifesciences.org/reviewed-pre...). You've pointed us to lots of great references for our revisions :)

Top-down feedback is ubiquitous in the brain and computationally distinct, but rarely modeled in deep neural networks. What happens when a DNN has biologically-inspired top-down feedback? 🧠📈

Our new paper explores this: elifesciences.org/reviewed-pre...

Just a couple days until Cosyne - stop by [3-083] this Saturday and say hi! @nandahkrishna.bsky.social

Hi BlueSky fam, for my first post and to celebrate our recent paper being physically published I thought I’d do a summary thread!

This has been my most favourite (and toughest) work to date.

Please help share around!!

www.cell.com/cell/abstrac...
(Reach out if you can’t access)

How do interneurons reshape neural responses? I'm excited to present work with @eerosim.bsky.social at #NeurIPS2024 that proposes a nonlinear recurrent circuit model motivated by efficient coding theory.

Poster: 4:30p on Fri, Dec 13
Paper: openreview.net/forum?id=ojL...

Why does #compneuro need new learning methods? ANN models are usually trained with Gradient Descent (GD), which violates biological realities like Dale’s law and log-normal weights. Here we describe a superior learning algorithm for comp neuro: Exponentiated Gradients (EG)! 1/12 #neuroscience 🧪

11. We’re looking forward to your feedback, and we hope that some of you will be interested in testing aspects of our model!

10. To summarize: we’ve proposed a model of the hallucinatory effects of classical psychedelics, wherein hallucinations are caused by an increase in top-down inputs ordinarily reserved for offline generative replay underlying a form of representation learning in the brain.

9. We conclude our study by providing a variety of testable predictions that experimental neuroscientists could use to validate or invalidate our model.

8. Furthermore, consistent with the Entropic Brain Theory (Carhart-Harris et al. 2014), we show that simulated psychedelic administration in our model produces increases in stimulus-conditioned neural variability.

7. Next, we show that intermediate simulated psychedelic doses in our model cause large increases in synaptic plasticity at both apical and basal synapses, as seen in (Shao et al. 2021).

6. We next explored how our model could explain existing neural data. First, we show that Wake-Sleep learning induces strongly correlated tuning between apical and basal dendritic compartments, as has been observed experimentally (Beaulieu-Laroche et al. 2019; O’Hare et al. 2024).

5. Next, we point to experimental evidence that classical psychedelics may increase the influence of apical synapses on neural activity, while decreasing the influence of basal synapses. Simulating psychedelic doses this way in our models produces highly structured hallucinations.

We map the Wake-Sleep algorithm onto cortical architecture by proposing top-down, predictive synapses onto apical dendrites of pyramidal neurons dominate activity during the generative Sleep phase, while bottom-up synapses onto basal dendrites dominate during waking activity.

3. An ‘oneirogen’ is a compound that makes neural activity more dream-like. We propose that psychedelics shift neural activity towards a regime normally reserved for replay during sleep, used for learning. To model this form of learning, we use the classic Wake-Sleep algorithm (Hinton et al. 1995).

2. We put forward the ‘Oneirogen Hypothesis,’ arguing that psychedelics cause hallucinations because they hijack a system ordinarily used for learning in the brain.

The oneirogen hypothesis: modeling the hallucinatory effects of classical psychedelics in terms of replay-dependent plasticity mechanisms Classical psychedelics induce complex visual hallucinations in humans, generating percepts that are coherent at a low level, but which have surreal, dream-like qualities at a high level. While there a...

1. Hi all: I’m here to advertise our new preprint: www.biorxiv.org/content/10.1..., with Fabrice Normandin, @tyrellturing.bsky.social, and @glajoie.bsky.social!