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Intertrial unconditioned stimuli differentially impact trace conditioning
Douglas A Williams1, Travis P Todd2, Chrissy M Chubala2
1Department of Psychology, University of Winnipeg, Winnipeg, MB, R3B 2E9, Canada. d.williams@uwinnipeg.ca.
Learning & Behavior
|August 7, 2016
Summary
Appetitive conditioning in rats shows that introducing unconditioned stimuli (USs) during the intertrial interval can make the trace conditioned stimulus (CS) inhibitory. This occurs even when the CS offset elicits a conditioned response, suggesting complex temporal learning.
Area of Science:
- Behavioral Neuroscience
- Learning and Memory
- Animal Behavior
Background:
- Trace conditioning involves a temporal gap between the conditioned stimulus (CS) and unconditioned stimulus (US).
- The impact of unsignaled USs within the intertrial interval on trace conditioning is not fully understood.
- Appetitive conditioning paradigms are crucial for studying associative learning mechanisms.
Purpose of the Study:
- To investigate how unsignaled unconditioned stimuli (USs) presented during the intertrial interval affect appetitive trace conditioning in rats.
- To determine if the temporal dynamics of the conditioned stimulus (CS) duration are altered by intertrial USs.
- To explore the inhibitory or excitatory nature of the trace CS under these experimental conditions.
Main Methods:
- Rats were subjected to three experiments involving a 120-s trace conditioned stimulus (CS) with unsignaled unconditioned stimuli (USs) in the intertrial interval.
- US timing relative to CS offset was varied: embedded, trace, and delay conditions.
- Behavioral suppression during the CS and unreinforced probe trials were used to assess learning.
- Summation and retardation tests were employed to confirm the inhibitory properties of the CS.
Main Results:
- Intertrial USs most suppressed responding during the CS in the trace group, followed by the delay and embedded groups.
- Probe trials revealed temporally specific learning, forming a bell-shaped curve around the US arrival time.
- Summation and retardation tests indicated that the trace CS acquired inhibitory properties when intertrial USs were present.
- Despite CS inhibition, CS offset still elicited a temporally precise conditioned response.
Conclusions:
- Unsignaled USs in the intertrial interval can induce inhibitory properties in a trace conditioned stimulus (CS).
- The temporal specificity of learning persists, creating a complex interplay between inhibitory CS elements and excitatory stimuli linked to CS termination.
- A modified microstimulus temporal difference model is proposed to explain these findings in appetitive conditioning.
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