Inter-pellet interval extension to reduce hoarding?

[Cayla Murphy]

Hi everyone,

I am considering extending the delay between when a pellet is taken and the next one is dispensed from 2 seconds to 10 seconds to try and reduce hoarding behavior in food restricted mice on free feeding. I have observed that mice take around 13-15 seconds to consume a pellet, so I do not think this delay will be too long, but what does everyone else think? Will this significantly impact their feeding behavior? And will this help reduce the hoarding problem I have seen? I saw in the forum that people have been switching to FR1 over free feeding to reduce hoarding but I do not want to add an element of a work requirement to my experiment at risk of changing their behavior too much. I think I will try this anyway but I am curious to know everyone's thoughts!

Best,

Cayla

[Lex]

Hi Cayla,

We actually ran this exact experiment, extending the timeout after each pellet taken to 30s (this experiment is a bit buried in a bioRxiv preprint, I'm pasting the relevant figure below).  We were trying to figure out why mice take fewer pellets in FR1, and test if slowing down their Free-feeding behavior would cause them to reduce pellets taken to the level of FR1.  Surprisingly, adding a 30s timeout did not reduce the number of pellets taken at all! I think on a Free feeding paradigm they do a combination of hoarding (taking and dropping full pellets) and just plain messiness that grinds up pellets and results in extra pellets taken when compared to FR1.  There is a paper from the Speakman group supporting this with ad lib feeding in home-cages. My hunch is that on FR1 they only take pellets when they are hungry, and in this state they eat most of the pellets they take.  But on Free feeding (or in home-cages with ad lib food provided) they interact with food at times when they are not hungry, and in these cases are more likely to drop pellets or grind up food without eating it, resulting in a higher total amount of pellets taken. 

That said, I'd be really curious what you find if you repeat this experiment as well! Best, -Lex

We also considered how mice consumed pellets more slowly within meals in the FR1 vs. Free task (Fig 1D), which would allow more time for satiety signals to reach the brain (23). To test if this accounted for the difference in total pellets taken, a new group of mice (n = 9, 4M/5F) completed a modified version of the Free task, where a 30s timeout (similar to the average time between pellets on the FR1 task, Fig 1D) was imposed before each new pellet was dispensed. This did slow down their rate of eating (Fig S2A significant effect of Task F(2,24) = 223.6, p < 0.001) but did not decrease the overall number of pellets taken per day. These same mice also completed the FR1 task, which confirmed that requiring these mice to nose-poke decreased pellets taken (Fig 2C-D significant effect of Task F(2,24) = 67.7 p < 0.001, post-hoc t-tests Free vs. Free with Timeout: p=0.52 Free vs FR1 and Free-Timeout vs FR1, p<0.001 for both).

 

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[Cayla Murphy]

Hi Lex,

Thank you so much for this information! I will read your paper and report back once I try extending the timeout.

Best,

Cayla

[Victor Cazares]

Hi Cayla,

From a learning theory perspective, adding a delay between the behavior and the reinforcer may “impair” acquisition. You may consider doing training with the short delay and then extending after they reliably nose poke. The other thing I can think of is that you may observe an increase in nose poking behavior between trials. If the goal is just to measure feeding, then it may not matter. But if there is a learning component to your study, you will want to account for all these differences in behavior.

Hope this helps,

Victor