Jason Shepherd

🇿🇦🇳🇿🇺🇸Professor of Neurobiology @UUtah. Molecular mechanisms of memory, repurposed transposons, and virus-like intercellular signaling. Personal opinions.

[Jason Shepherd @JasonSynaptic]

Very excited for our new paper, now out in @CellCellPress! /🧵The protein Tau forms intracellular toxic tangles in neurons in Alzheimer’s disease and Tauopathies. Tau pathology slowly spreads from cell-to-cell but the mechanisms of Tau transmission are not clear. /1

[Jason Shepherd @JasonSynaptic]

Worth the watch, even if you don’t live in Texas!

[Team Talarico @TeamTalaricoHQ]

Texas was built by hope. By people who had no business believing — but believed anyway.

To every Texan who’s ever wondered if anyone in power is paying attention: We are taking our state back.

Because a little bit of hope is a dangerous thing.

[Jason Shepherd @JasonSynaptic]

@NutritionNerd She didn’t make the cut! Kidding. Here you go.

[Jason Shepherd @JasonSynaptic]

Beautiful Fall hiking weather in the ‘hood this afternoon in between grant reviews 😍

[Jason Shepherd @JasonSynaptic]

🤣

[Ulugbek S. Kamilov @prof_kamilov]

I always considered myself a well-rounded person. Then I got a PhD and became an expert on a topic that only 7 people understand. Four of them think I’m an idiot.

[Jason Shepherd @JasonSynaptic]

@steven_nikolic I'm not sure what you mean. AI has leapt heaps and bounds, but it's arguable that AI will never be conscious or even approximate it (despite many claiming otherwise).

[Jason Shepherd @JasonSynaptic]

When I was an undergrad, I asked a famous neuroscientist about consciousness and he said "that's for chats at the bar". Seeing the progress here is awesome and I'm excited to see where Doris takes these findings! IMO, we won't understand consciousness without knowing how...

[Doris Tsao @doristsao]

The outpouring of interest in our paper has been … a bit insane.

May I make four points?

1. We have not shown that “consciousness has a frame rate.”

I can see why people draw this conclusion: we report that inferotemporal and prefrontal cortex alternate between conscious and suppressed states roughly every 60 ms during binocular rivalry.

Consciousness depends on many brain areas, and our paper reports results from only a few select nodes.

We still don’t know how conscious access works--the actual recipe for generating conscious experience. What we have shown is that deep in the brain there is an extremely strong signal, rich enough to reconstruct a high-dimensional face in detail, that is inaccessible to consciousness. As I argued in the original tweet, this makes the problem of conscious access a lot more experimentally tractable. But to claim “consciousness has a frame rate,” one would need to have actually solved the mechanism for conscious access and shown that this mechanism operates at a frame rate.

While we currently don’t know conclusively one way or the other (see VanRullen & Koch, 2003 for a review of positive evidence), I personally am skeptical that consciousness has a frame rate. I believe the brain, within posterior parietal cortex, has continuous tracking mechanisms that actively represent the persistence of matter, including ourselves as physical bodies. The coupling between these persistent tracking processes and feature representations across the brain (like those in face patches) is, I think, the essential mechanism of conscious access.

This coupling need not happen at the rate of inferotemporal alternations (and inferotemporal cortex itself may not even alternate outside of the artificial situation of binocular rivalry). As an analogy: imagine the area crucial for conscious access holding a steady drone note, while inferotemporal cortex alternates between two notes, one in harmony and one dissonant. Inferotemporal content might couple to the drone only at moments of harmony, yet experience would still be continuous, because the drone itself (the tracking process that I believe is at the core of conscious perception) never stops. And areas without conflicting content, like auditory cortex during visual rivalry, could stay in continuous harmony with the drone.

In sum, there is no reason to conclude from our study that consciousness is discrete, with a "frame rate."

2. Our results resemble Jezek et al. 2011 (as @jjsakon notes).

Jezek et al. trained rats in two boxes that were identical except for their lighting cues, so that hippocampal place cells formed two distinct maps, one per box. They then “teleported” the rat by abruptly switching the lights. For a few seconds afterwards, CA3 place-cell activity flickered between the two maps, synced to the theta cycle (~125 ms).

@StanDehaene first pointed this paper out to me, and reading it blew me away. To my mind it is the strongest evidence for a bistable attractor in the brain, because the competing maps are stored within the hippocampus itself.

I think the phenomenon we see may be very similar at the circuit level: a bistable attractor network within inferotemporal cortex that alternately converges to one of two patterns, as cells in face patches work together to build a coherent representation of the input. In our case, both images are present in the input, so the competition could arise within IT or be inherited from earlier areas such as V1--recording there is an important next step. (It also still puzzles me that we didn’t see strong coherence between face patches ML and AM.)

More broadly, what’s different about our paper is the brain area (inferotemporal cortex, often modeled as a feedforward DNN) and the ability to relate the two competing patterns to consciousness, with one granted conscious access and the other not.

3. Please comment on bioRxiv!

The Twitter attention has been cool, but I really hope colleagues will be generous enough to post detailed commentary on bioRxiv, where there are currently 0 comments. As @seemaychou points out, peer review doesn’t have to come from just three anonymous reviewers. We would be truly grateful for your critical feedback.

4. Stay tuned

This work was done at Caltech, Berkeley, in collaboration with @EngelTatiana at Princeton, funded by NIH and HHMI.

I hope to share our vision soon for how we can solve consciousness @AsteraInstitute

[Jason Shepherd @JasonSynaptic]

info from the peripheral nervous system is integrated into subjective experience and built during development. But even having some sort of neural correlate of consciousness is huge and hypothesis generating at the least.

[Jason Shepherd @JasonSynaptic]

@may_khanna I thought he was a bit condescending at first but Tommy’s question was clearly asked in bad faith…and that was clear when he admitted his Christian nationalist agenda at the end.

[Jason Shepherd @JasonSynaptic]

This is the way.

[Dr. Abdul El-Sayed @AbdulElSayed]

This is Tommy. Tommy had a question about my allegiances. Listen to the end to hear about his.

[Jason Shepherd @JasonSynaptic]

@YSPTSPS @lpachter @OdedRechavi Here’s a great high level summary! But as @lpachter says, if the data isn’t available…then it all comes down to being able to evaluate their analysis. The temporal switching is unexpected and at the least is hypothesis generating!

[Azad Balabanian @Azadux]

I had trouble fully unpacking what this paper actually was measuring, what its findings were, and what the implications are for human/primate consiousness

so i had Claude read through the paper and this thread, compose a script, and create an explainer video

[Jason Shepherd @JasonSynaptic]

Utes made that waaayy too close 😮‍💨😮‍💨

[Jason Shepherd @JasonSynaptic]

BYU wins the religious war! Now the holy war (Utah vs BYU) gonna be huuuge.

[Jason Shepherd @JasonSynaptic]

@arjunrajlab Transcends science to...society. Look around...we are doomed 🤪

[Jason Shepherd @JasonSynaptic]

@zandawala @NutritionNerd I thought that was part of the citizenship test 😆

[Jason Shepherd @JasonSynaptic]

Me: have you seen Bladerunner?

@NutritionNerd: no, I couldn’t tell you what it’s about.

Me: well, the newer one has Ryan Gosling who you like!

@NutritionNerd: oh cool. Is it about hockey?

Me: ….

[Jason Shepherd @JasonSynaptic]

@NutritionNerd https://t.co/iudKxKxyuB

[Jason Shepherd @JasonSynaptic]

@NutritionNerd It was a good guess but the opposite of the movie’s vibes 😘

[Jason Shepherd @JasonSynaptic]

@RandyStout18 @jdpereira @NutritionNerd @grok @imagine lol

[Jason Shepherd @JasonSynaptic]

@grok @jdpereira @NutritionNerd 😂

[Jason Shepherd @JasonSynaptic]

@ScottRussoPhD @paulkenny @ericnestler Congrats Scott!