Preparing some slides on my favourite topic of the moment - #HippocampalReplay - for some colleagues, starting from lecture slides I made about 8 years ago...
and I keep crossing stuff or adding "BUT see xx" or "actually not" or "Now controversial!" to about half of the results that I was taking from granted 8 years ago 👀
Is there any such thing as a scientific fact?!
Here's a very interesting paper from the #KeinathLab:
In the absence of task or reward, #PlaceCells appear to reflect the past history of behavioural biases, i.e. the accumulated past paths taken by each individual mouse. I am actually starting to think that #HippocampalReplay is doing a similar thing - just reflecting an average of the individual's past behaviour, and that all supposed "coding" of reward is purely driven by this (notice how reward "coding" always seems to happen in cases where reward biases the behavioural patterns..) 👀🧠🤔
If you want to study #HippocampalReplay... Use ephys, not #CalciumImaging!!
(Calcium imaging doesn't detect single spikes well, but replay mostly involves single spikes)
#Neuroscience #SpatialCognition #Hippocampus
Thinking of organizing a regular (every 2 months) full-online journal club on #HippocampalReplay (and more generally, internally-generated sequences phenomena).
Would anyone from here be interested? I had been organizing something similar (IGSJC) where the first author presents a recent paper, but it has only been every year or so, this would be more regular and not necessarily presented by the first author.
The goal would be to keep up with the replay literature with a critical (and fair) approach. If you are interested can you let me know your timezone? 🧠
Heading off to the #EBBS2025 conference in Bordeaux!
I will present a poster there on our latest #HippocampalReplay findings (replay does not do planning, but seems to support reward-learning instead, in a flexible spatial planning task), and co-lead a symposium with the great John Widloski, also on replay!
We have an amazing speaker list with John himself, Lisa Genzel, Jacob Bakermans and Elisa Massi!
Check the full programme here: https://ebbs2025.azuleon.org/programme_overview
Will you be there?!
I keep going back to this question about #TemporalCreditAssignment and #HippocampalReplay:
As an "agent" you want to learn the value of places and which places are likely to lead to reward;
-1) if a place leads to higher than expected reward, you'll want to propagate back the reward info from the reward throughout the places that led to the reward. If replay does that you should see an increase of replay at a new reward site and the replay sequences should start at the reward and reflect what you just did to reach it. Right?
-2) if a place leads to lower than expected reward, you'll also want to propagate that lowered value, pretty much in the same way, so if replay does that you should see a similar replay rate and content for increased OR decreased reward sites. Right?
-3) if a place has had unchanged reward for a while and you're just in exploitation mode (just going there again and again because you know that's the best place to go to in the environment) then you shouldn't need to update anything and replay rate should be quite low at that unchanged reward side. Right?
That's not at all what replay is doing IRL, so does that mean replay is not used for temporal credit assignment? Or did I (very likely) miss something?
#Neuroscience #ComputationalNeuroscience #DecisionMaking #Hippocampus
Recent opinion piece on awake #HippocampalReplay which takes together a lot of recent results and concludes that:
This paper ⬆️ from Caitlin Mallory is now out in Science! Great to see a #HippocampalReplay paper there, and very well deserved!
The time course and organization of hippocampal replay
From #FosterLab, maybe soon the #MalloryLab??
@johnwidloski and I are co-organizing a symposium on #HippocampalReplay at the #EBBS25 in Bordeaux!
Our goal: From the state of the art in awake replay models & existing data, determine the next big questions and most informative future experiments to finally figure out what is awake replay for!
Our speakers:
Meeting dates: 28 June to 1 July 2025 (our symposium is on the last day
Programme: https://ebbs2025.azuleon.org/programme
The abstract submission deadline for posters (and early bird registration) is on 31 March 2025 - I hope to see you there!
A short commentary by the great Anna Gillespie on awake replay:
Ruminating on replay during the awake state
#GillespieLab (https://www.gillespie-lab.com/)
Interesting bits:
"replay during sleep is generally thought to occur in the forward direction"
I believe this is true too, but has anyone actually analyzed it? It could be done on several existing datasets...
"The idea that awake replay might serve a planning role was broadly adopted by the field, even though direct experimental evidence [...] has been slow to emerge"
YES because replay is not related to immediate planning, however nice it would be if it was
"We, as a field, also need to be more precise with our terminology. For instance, what exactly should we consider evidence of ‘planning’ or ‘deliberation’ in an animal model? "
YES
Related: history of the 'genesis' of #ThetaSequences narrated in this retrospective by @adredish: Mental Time Travel: A Retrospective
(original post:
https://neuromatch.social/@adredish/113662497894186335) #RedishLab
I'd actually argue that replay, and not theta sequences, might be closer to mental time-travel... but we probably don't know enough about either to be sure yet!
El Duvelle Neuro