First research meeting of 2020!
@FFiebig will discuss A Hybrid Oscillatory Interference/Continuous Attractor Network Model of Grid Cell Firing by Daniel Bush and Neil Burgess
Wed Jan 1, 2020 - 10:15AM PST
I’m looking forward to this. In anticipation I just rewatched @FFiebig’s interview, and finally understood what an attractor is. For a quick reminder, watch this part for Florian’s excellent explanation and a bit further why attractors could be such an important link to explain short term memory and even the binding problem.
Absolutely fascinating talk. Thanks so much, guys.
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Live in about 30 minutes.
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I watched the meeting presentation today and quickly read the papers shown in the meeting. Thanks for the presentation and thoughtful questions and discussion. Thank you Florian. Great choice of topic.
The subject is a difficult grok. At least for me. Here is what I thought about it, from my place of ignorance.
Theta phase precession of grid and place cell firing in open environments - PubMed. Theta phase precession of grid and place cell firing in open environments
A. Jeewajee1, C. Barry1,3,4, V. Douchamps5, D. Manson1,2, C. Lever5 and N. Burgess3,4
Article in Philosophical Transactions of The Royal Society B Biological Sciences · February 2014.
The main point of the papers is not very easy to understand. Grid and Place cells have local oscillations in field potentials, or LFP. And a brain moving through a space (with intention or awareness) has observable signals that can be plotted on the Unit Circle of a phase/distance diagram that shows some interesting, if noisy, patterns that precede or precess the theta angle on the unit circle of the normal phase space of the LFP. Which is brilliant, truly.
Given the data shows a “phase precession relative to the normal oscillations of the local field potentials, in both place and grid cells when a rodent’s [awareness] moves through a known space,” and “the temporal dynamics of firing varies between slow runs and fast runs so that phase of firing codes for distance travelled”. Gives me a few ideas:
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Awareness or intentionality of movement might cause/create this precession of theta phase in the grid field unit circle of place cells.
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The Neocortex has a mechanism for awareness of (aka predicting) distance in movement. Could these papers show how? These papers show a strong correlation between movement and wave-like precession in firing rates of place cells and grid cells – which I’m thinking might be the physiological coding mechanism for awareness of position or distance in movement. I use the term awareness to mean “locked into where I am and will be very soon at the speed I’m moving.” Also, “Don’t trip.”
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Neural activations ripple in a manifold like a surface with pulsing waves in grid cells. Movement (with a brain) uses these waves, and we know that prediction is an essential part of sensor-motor feedback, as well as many other things. Since 2007 or 2014 the precession of the the firing rates of grid-neurons has been observed and highly correlated with movement. Which really seems to answer many questions at the same time. Certainly worth a deeper research.
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An experiment I would suggest is to distract/disrupt the attention of the rodents at various test places on their travel through their cage. If the phase precession is related to awareness or intention in the brain, then the distraction or unexpected disruption will disturb the data collected from the neurons and the precession will be systematically changed in angle or phase, differently from the relatively stable correlation of phase with distance travelled across fast and slow runs. My model is that when you are distracted completely you are momentarily “in a new place.”
Fanciful idea: Awareness is wave-riding your thetas. You are consciously aware of your movement only if your grid cells are firing with a phase theta precessed by just the right amount – like riding a wave of prediction where you are and will be next. Neural systems evolved for movement with grid cells. All awareness is wave-riding a theta precession movement through spaces of some kind, using grid cells of some kind. Since awareness of distance and location is fleeting, and disrupt-able, we should be able to measure that using the same methods in controlled ways with various stimuli. I’m also wondering if consciousness, and the disruption of consciousness is related to the same neural phase unit circle oscillations, and only when you’re “locked-in to your thetas” are you able to be aware. Maybe?
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Interesting thoughts.
What I’m looking forward to most is what exactly generates the dendritic pulse that combined with the somatic oscillation causes the precessing signal. @FFiebig suggested that it is highly reduced in amplitude when the agent stops moving.
So it could be muscle feedback, but it must be much more complicated than that since we use many muscles to move, and we can omit using certain muscles and still move. I think @subutai or @mrcslws in an earlier research meeting mentioned an experiment with monkeys immobilized in a wheel chair being carted around still showed grid cells.
Also I would be careful in using the word awareness. It would suggest that sleepwalkers do not generate grid cells, since they are not aware. Yet sleepwalkers can do impressive feats like walking up and down stairs and navigate well known rooms in darkness.
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Thanks for your response.
I’m just guessing, after watching today’s talk by Murray Sherman about Thalamal-Cortical System 1, given at the Simons Institute, and streamed today on Twitch by Rhyolight that the Thalamus is actively involved in processing sensory signals and is intimately involved in excitatory and inhibitory “tuning” as I would call it. Since this system is such a core structure and the functions we are wondering about are also core in an evolutionary sense, then maybe the Thalamus is what generates/listens to the dendritic pulses of the precessing grid cell signals.
That is a good point. I will think more about the question, ignoring the warning 
. Are sleep walkers really aware? I would suggest we develop an experiment to test if sleep walkers show the “awareness” pattern: locked-in precession of the the firing rates of grid-neurons. My hunch is that the pattern will not be highly correlated with movement because the activity is done with less or no “awareness”. Memory, yes. Thalamus must be involved, yes. It would be interesting to see if different states of consciousness affects grid cells firing with a phase theta precessed by just the right amount. Yee Haw!
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By the way, I’m trying to come up with a term for: locked-in precession of the the firing rates of grid-neurons. It would be good to have a shorter, better phrase for that.
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What do you mean with locked-in?