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Trace conditioning: insights from invertebrate models on bridging the temporal gap
Veronica Rivi1, Aditya Ponkshe2, Ken Lukowiak3
1Department of Biomedical, Metabolic and Neural Sciences, University of Modena and Reggio Emilia, Modena, Italy.
Biology Letters
|March 24, 2026
Summary
Trace conditioning, forming associations over time, is not exclusive to vertebrates. Invertebrates like snails demonstrate this learning, challenging previous assumptions about its neural basis.
Area of Science:
- Neuroscience
- Comparative Psychology
- Animal Behavior
Background:
- Trace conditioning, forming associations between temporally separated stimuli, was historically believed to require complex vertebrate neural structures like the hippocampus.
- Emerging evidence suggests invertebrates possess the capacity for trace conditioning, challenging its vertebrate exclusivity.
Purpose of the Study:
- To review current findings on trace conditioning in invertebrates.
- To propose a novel two-tier mechanistic model for trace learning integrating stimulus salience and attention.
- To highlight the great pond snail (*Lymnaea stagnalis*) as a model organism for studying trace conditioning.
Main Methods:
- Review of existing research on invertebrate trace conditioning.
- Proposal of a theoretical framework for trace learning.
- Suggesting experimental paradigms involving manipulation of conditioned stimulus-unconditioned stimulus intervals, stimulus salience, and distractor presence.
Main Results:
- Trace conditioning is demonstrably present in invertebrates with simpler nervous systems.
- A proposed model emphasizes rapid, stimulus-specific encoding and attention-based memory in trace learning.
- The great pond snail (*Lymnaea stagnalis*) is identified as a suitable model for testing this framework.
Conclusions:
- Trace conditioning is a more widespread cognitive ability across the animal kingdom than previously thought.
- The proposed mechanistic model offers a framework for understanding trace learning in diverse species.
- Future research can utilize this framework to investigate the neural and behavioral mechanisms of attention-based memory in trace conditioning.
