Source Paper
Information, certainty, and learning
Harris JA, Gallistel CR
eLife • 2026
Classical Conditioning with Variable CS-US Intervals
Objective: To measure classical conditioning acquisition using variable CS-US intervals with different temporal relationships between conditioned stimulus and food reinforcement
This is a Classical Conditioning with Variable CS-US Intervals protocol using Rat as the model organism. The procedure involves 10 procedural steps, 4 equipment items, 2 materials. Extracted from a 2026 paper published in eLife.
Model and subjects
Rat • Sprague Dawley • Female • 8-10 weeks • 176
Study window
~3 day study window
Core workflow
Housing and food restriction • Daily feeding schedule • Group assignment
Primary readouts
- Trial to acquisition using cumulative response rate analysis
- nDKL statistic for identifying learning onset
- Response rate during CS vs ITI periods
- Terminal response rate over final 5 sessions
Key equipment and reagents
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Protocol Steps
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Housing and food restriction
House rats in groups of 4 and implement food restriction 3 days before experiment
View evidence from paper
“Three days before commencing the experiment, they were placed on a restricted food schedule”
Daily feeding schedule
Feed rats daily ration 30 minutes after training session
View evidence from paper
“half an hour after the end of the daily training session, each tub received a ration”
Group assignment
Randomly allocate each tub of four rats to one of 14 experimental groups
View evidence from paper
“Each tub of four rats was randomly allocated to one of the 14 groups”
Skip magazine training
Begin experiment without preliminary magazine training
View evidence from paper
“The rats were not given magazine training. The experiment commenced with the first conditioning session”
Implement variable CS-US intervals
Use uniform distribution for CS-US intervals centered on group-specific T value
View evidence from paper
“the CS-US interval varied from trial-to-trial according to a uniform distribution centred on the value of T”
Set interval parameters
CS-US intervals range from 2s minimum to 2 × T-2s maximum
View evidence from paper
“the interval varied from a minimum of 2 s to a maximum of 2x T –2 s”
Configure inter-trial intervals
Use variable ITIs with uniform distribution and 15s minimum
View evidence from paper
“The ITI in each group also varied from trial-to-trial as a uniform distribution with a minimum of 15 s”
Set trial numbers per session
Use 10 trials per session for groups with C/T ratios 1.5-72, and 3 trials for higher ratios
View evidence from paper
“For the first 11 groups, there were 10 trials per session; for the remaining three groups, each session contained only three trials”
Conduct training sessions
Train all groups daily for 42 consecutive sessions
View evidence from paper
“continued for 42 sessions over 42 consecutive days”
Record magazine entries
Monitor photo-beam interruptions during CS and ITI periods
View evidence from paper
“Photo-beam interruptions by entry into the magazine were recorded during each CS and each ITI”