Abstract
Time perception is crucial to goal attainment in humans and other animals, and interval timing also guides fundamental animal behaviors. Accumulating evidence has made it clear that in associative learning, temporal relations between events are encoded, and a few studies suggest this temporal learning occurs very rapidly. Most of these studies, however, have used methodologies that do not permit investigating the emergence of this temporal learning. In the present study we monitored respiration, ultrasonic vocalization (USV) and freezing behavior in rats in order to perform fine-grain analysis of fear responses during odor fear conditioning. In this paradigm an initially neutral odor (the conditioned stimulus, CS) predicted the arrival of an aversive unconditioned stimulus (US, footshock) at a fixed 20-s time interval. We first investigated the development of a temporal pattern of responding related to CS-US interval duration. The data showed that during acquisition with odor-shock pairings, a temporal response pattern of respiration rate was observed. Changing the CS-US interval duration from 20-s to 30-s resulted in a shift of the temporal response pattern appropriate to the new duration thus demonstrating that the pattern reflected the learning of the CS-US interval. A temporal pattern was also observed during a retention test 24 h later for both respiration and freezing measures, suggesting that the animals had stored the interval duration in long-term memory. We then investigated the role of intra-amygdalar dopaminergic transmission in interval timing. For this purpose, the D1 dopaminergic receptors antagonist SCH23390 was infused in the basolateral amygdala before conditioning. This resulted in an alteration of timing behavior, as reflected in differential temporal patterns between groups observed in a 24 h retention test off drug. The present data suggest that D1 receptor dopaminergic transmission within the amygdala is involved in temporal processing.
Highlights
Time perception is crucial to survival and goal reaching in humans and other animals and interval timing which refers to the ability to time intervals between arbitrary events ranging from seconds to minutes, guides fundamental animal behaviors
EXPERIMENT 1: BEHAVIORAL ASSESSMENT OF INTERVAL TIMING IN ODOR FEAR CONDITIONING In this experiment, we analyzed the effects of conditioning on (1) the average global value of the recorded parameters when comparing pre-Cs vs. CS period and (2) their fine-grain temporal pattern during the CS odor
We demonstrated for one of the measures that this temporal pattern was linked to interval timing since changing the CS-US interval duration resulted in a proportional shift of the temporal response toward the new duration value
Summary
Time perception is crucial to survival and goal reaching in humans and other animals and interval timing which refers to the ability to time intervals between arbitrary events ranging from seconds to minutes, guides fundamental animal behaviors. Balsam and Gallistel (2009), Balsam et al (2010) proposed that these temporal relations are constantly and automatically encoded and are the foundation of associative learning They further suggested that this temporal learning occurs very rapidly and prior to the appearance of the anticipatory response Balsam et al (2010). Most studies investigating interval timing in animals use peak interval procedures (Bitterman, 1964) or temporal discrimination tasks (Stubbs, 1968) which both necessitate numerous conditioning sessions, precluding the observation of timing behavior at the beginning of learning
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