Timed excitatory conditioning under zero and negative contingencies

Area of Science:

• Behavioral neuroscience
• Animal learning and behavior

Background:

• Classical conditioning research traditionally emphasizes the importance of contingency (whether a conditioned stimulus signals a change in unconditioned stimulus occurrence).
• The role of temporal factors (when the unconditioned stimulus is expected) in conditioning is also recognized but often considered secondary to contingency.

Purpose of the Study:

• To investigate whether rats can form anticipatory responses to a conditioned stimulus (CS) even when it does not predict an increase in unconditioned stimulus (US) probability.
• To challenge the traditional view that a positive CS-US contingency is essential for successful conditioning.

Main Methods:

• Rats (Rattus norvegicus) were exposed to a conditioned stimulus (CS) paired with a food pellet unconditioned stimulus (US).
• The US was delivered at a fixed time during the CS, while USs also occurred probabilistically during the intertrial interval at rates equal to or higher than the CS rate.
• Experiments manipulated the rate of US occurrence during the intertrial interval relative to the CS.

Main Results:

• Rats demonstrated anticipatory behavior towards the CS, even when the CS signaled no overall increase or even a decrease in the probability of receiving a US.
• The temporal predictability of the US within the CS (when) appeared to be a stronger factor in driving anticipatory responses than the overall contingency (whether) between the CS and US.

Conclusions:

• The findings suggest that temporal factors ('when') in conditioning can be more critical than contingency ('whether') in establishing anticipatory responses.
• This challenges the established principle that a positive conditioned stimulus-unconditioned stimulus contingency is a prerequisite for successful conditioning.