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#ripples

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El Duvelle Neuro

I keep seeing studies (especially computational ones) citing the Ambrose et al. 2016 paper as proof that #HippocampalReplay is modulated by reward.

I don't think this result can be trusted...

  1. The time spent at low-speed at reward sites wasn't controlled. Rats probably left the unrewarded sites much faster, or would move a lot more there than when reward was present.
  2. The amount of ripples or replay is analysed in count per second. I believe this means seconds of any kind of behaviour, not just rest or low speed. But #Ripples and the related #Replay only happens when the rat is quasi-immobile. At low speed you might have 1 replay per second, while when moving it will be 0/s.
  3. A recent preprint (Mallory et al., 2024) suggests that after a few seconds at a reward location, reverse replay dominates. Ambrose et al. specifically show an increase of reverse replay for those more rewarded locations. If rats indeed spent more time at the most rewarded location, they would be in reverse replay mode, fully explaining the results without the need to invoke any kind of value processing.

I might have missed something (if so let me know) but I am now completely unconvinced by the 2016 paper. What do you all think?

linkinghub.elsevier.comReverse Replay of Hippocampal Place Cells Is Uniquely Modulated by Changing RewardHippocampal replays are episodes of sequential place cell activity during sharp-wave ripple oscillations (SWRs). Conflicting hypotheses implicate awak…
#Hippocampus#ValueCoding
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💧🌏 Greg Cocks

Vortex Trapping Of Suspended Sand Grains Over Ripples
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doi.org/10.1029/2023JF007620 <-- shared paper
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“KEY POINTS
• Observations of vortex-trapped grains suggest delayed settling of advected grains, as well as delayed advection of grains mobilized from the bed
• Quantitative comparisons of vortex-trapped sand grains compared well with theoretical formulations by Nielsen (1992, doi.org/10.1142/1269) for a forced vortex
• Improved understanding of vortex trapping effects on sediment dynamics may decrease uncertainty in large-scale coastal model predictions..."
#spatial #model #modeling #water #hydrology #hydrodynamics #vortex #sand #sediment #transport #sedimentation #sedimentology #morphodynamics #fluiddynamics #ripples #coast #coastal #research #velocimetry #suspension #experimentation #dynamics #geology #processes #geomorphology #geomorphometry #vortextrapping #sand #grains #flow #ripple #sandwaves #ripples

Illustration of the vortex core (blue arrows) distinct from the boundary shear and background turbulence (gray arrows) along the sand ripple. The black streamline indicates the freestream flow direction at this time step while the vortex is developing along the ripple slope. The double-headed arrow indicates that the free-stream velocity is oscillatory.
photo - experimental setup of particle image and tracking velocimetry system in the Small-Oscillatory Flow Tunnel at the United States Naval Research Laboratory at Stennis Space Center, Mississippi, United States of America. Three high-speed cameras and a downward-looking Neodymium-doped yttrium aluminum garnet (Nd:YAG) laser were aimed at the test section of the rippled sand bed.
charts / figures - Vorticity and grain trajectories. (a) Freestream horizontal velocity with time steps of snapshots indicated. Instantaneous velocities are overlaid on vorticity ((b)–(g)), shown at every fourth vector, with scale vector and the brown line delineating the ripple shown. Trajectories of some vortex-trapped sediment grains are highlighted with start and end times indicated by matching triangle and square symbols in (a). Times for the semi-circular paths are indicated with circle markers. Gray circles estimate regions of highest fluid vorticity, with direction of the fluid parcels indicated by gray arrows, and quadrants of the vortex outlined.
photo - sand waves / ripples formed on the shores of Broad Bay at First Landing State Park, Virginia, USA
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