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Time-specific extinction and recovery of the rabbit's (Oryctolagus cuniculus) conditioned nictitating membrane
Joanne E Dudeney1, Kirk N Olsen, E James Kehoe
1School of Psychology, University of New South Wales, Sydney, NSW 2052, Australia.
Insights
Extinction of conditioned responses (CRs) can occur even with continuous conditioned stimulus (CS) and unconditioned stimulus (US) pairings. This study demonstrates extinction hallmarks like spontaneous recovery and peak recovery in rabbit nictitating membrane responses.
Area of Science:
- Neuroscience
- Behavioral Psychology
- Learning and Memory
Background:
- Traditional extinction protocols involve separating conditioned stimuli (CS) from unconditioned stimuli (US).
- Understanding the mechanisms of extinction is crucial for developing effective behavioral therapies.
- Previous models suggest extinction involves changes in CS processing or US representation.
Purpose of the Study:
- To investigate the phenomenon of conditioned response (CR) extinction under continuous CS-US pairings.
- To examine the role of interstimulus intervals (ISIs) in CR extinction.
- To challenge existing theories of extinction by providing evidence for alternative mechanisms.
Main Methods:
- Rabbits were trained with a conditioned stimulus (CS) paired with an unconditioned stimulus (US) using two interstimulus intervals (ISIs): 150 ms and 500 ms.
- The 150-ms ISI was selectively removed during training, and the resulting CRs were analyzed.
- Subsequent training with a new CS at the 150-ms ISI was introduced, followed by tests of the original CS.
Main Results:
- Conditioned responses (CRs) initially exhibited double peaks corresponding to the two ISIs.
- Removal of the 150-ms ISI led to a decline in its corresponding CR peak and spontaneous recovery between sessions.
- Reintroduction of the 150-ms ISI with a new CS resulted in strong recovery of the original, extinguished CS's 150-ms peak.
Conclusions:
- Extinction can occur without separating CS and US, challenging traditional views.
- Results support models where the CS is encoded as a cascade of microstimuli.
- Findings necessitate a re-evaluation of extinction theories focusing on CS processing, US representations, and context.
Abstract:
Extinguishing a conditioned response (CR) has entailed separating the conditioned stimulus (CS) from the unconditioned stimulus (US). This research reveals that elimination of the rabbit nictitating membrane response occurred during continuous CS-US pairings. Initial training contained a mixture of 2 CS-US interstimulus intervals (ISIs), 150 ms and 500 ms. The CRs showed double peaks, one for each ISI. When the 150-ms ISI was removed, its CR peak showed 2 hallmarks of extinction: a decline across sessions and spontaneous recovery between sessions. When a further stage of training was introduced with a distinctive CS using the 150-ms ISI, occasional tests of the original, extinguished CS revealed another hallmark of extinction, specifically, strong recovery of the 150-ms peak. These results support both abstract and cerebellar models of conditioning that encode the CS into a cascade of microstimuli, while challenging theories of extinction that rely on changes in CS processing, US representations, and contextual control.
