Relative temporal representations in Pavlovian conditioning

Temporal encoding: Relative and absolute representations of time guide behavior

Temporal information-processing is critical for adaptive behavior and goal-directed action. It is thus crucial to understand how the temporal distance between behaviorally relevant events is encoded to guide behavior. However, research on temporal representations has yielded mixed findings as to whether organisms utilize relative versus absolute judgments of time intervals. To address this fundamental question about the timing mechanism, we tested mice in a duration discrimination procedure in which they learned to correctly categorize tones of different durations as short or long. After being trained on a pair of target intervals, the mice were transferred to conditions in which cue durations and corresponding response locations were systematically manipulated so that either the relative or absolute mapping remained constant. The findings indicate that transfer occurred most readily when relative relationships of durations and response locations were preserved. In contrast, when subjects had to re-map these relative relations, even when positive transfer initially occurred based on absolute mappings, their temporal discrimination performance was impaired, and they required extensive training to re-establish temporal control. These results demonstrate that mice can represent experienced durations both as having a certain magnitude (absolute representation) and as being shorter or longer of the two durations (an ordinal relation to other cue durations), with relational control having a more enduring influence in temporal discriminations. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Rescaling of temporal expectations during extinction

Previous research suggests that extinction learning is temporally specific. Changing the conditioned stimulus (CS) duration between training and extinction can facilitate the loss of the conditioned response (CR) within the extinction session but impairs long-term retention of extinction. In 2 experiments using conditioned magazine approach with rats, we examined the relation between temporal specificity of extinction and CR timing. In Experiment 1, rats were trained on a 12-s, fixed CS-unconditional stimulus interval and then extinguished with CS presentations that were 6, 12, or 24 s in duration. The design of Experiment 2 was the same except rats were trained using partial rather than continuous reinforcement. In both experiments, extending the CS duration in extinction facilitated the diminution of CRs during the extinction session, but shortening the CS duration failed to slow extinction. In addition, extending (but not shortening) the CS duration caused temporal rescaling of the CR, in that the peak CR rate migrated later into the trial over the course of extinction training. This migration partially accounted for the faster loss of the CR when the CS duration was extended. Results are incompatible with the hypothesis that extinction is driven by cumulative CS exposure and suggest that temporally extended nonreinforced CS exposure reduces conditioned responding via temporal displacement rather than through extinction per se. (PsycINFO Database Record

Associative learning and timing

Associative learning and timing are clearly inter-related, but are they separate processes or is timing a core part of the associative structure? Emerging research suggests that temporal information is acquired rapidly and that CR's are timed correctly from the start of associative learning. Moreover, specific temporal knowledge can be disclosed even in cases where CR's were not emitted. Timing is not only critical for CR timing, but also contributes to CR expression through the comparison of reinforcer rates, and through the formation of temporal maps. A conceptual framework is proposed in which timing is a core part of the content of associative learning.

Temporal regularity determines the impact of electrical stimulation on tactile reactivity and response to capsaicin in spinally transected rats

Nociceptive plasticity and central sensitization within the spinal cord depend on neurobiological mechanisms implicated in learning and memory in higher neural systems, suggesting that the factors that impact brain-mediated learning and memory could modulate how stimulation affects spinal systems. One such factor is temporal regularity (predictability). The present paper shows that intermittent hindleg shock has opposing effects in spinally transected rats depending upon whether shock is presented in a regular or irregular (variable) manner. Variable intermittent legshock (900 shocks) enhanced mechanical reactivity to von Frey stimuli (hyperreactivity), whereas 900 fixed-spaced legshocks produced hyporeactivity. The impact of fixed-spaced shock depended upon the duration of exposure; a brief exposure (36 shocks) induced hyperreactivity whereas an extended exposure (900 shocks) produced hyporeactivity. The enhanced reactivity observed after variable shock was most evident 60-180 min after treatment. Fixed and variable intermittent stimulation applied to the sciatic nerve, or the tail, yielded a similar pattern of results. Stimulation had no effect on thermal reactivity. Exposure to fixed-spaced shock, but not variable shock, attenuated the enhanced mechanical reactivity (EMR) produced by treatment with hindpaw capsaicin. The effect of fixed-spaced stimulation lasted 24h. Treatment with fixed-spaced shock also attenuated the maintenance of capsaicin-induced EMR. The results show that variable intermittent shock enhances mechanical reactivity, while an extended exposure to fixed-spaced shock has the opposite effect on mechanical reactivity and attenuates capsaicin-induced EMR.

Time and Associative Learning

In a basic associative learning paradigm, learning is said to have occurred when the conditioned stimulus evokes an anticipatory response. This learning is widely believed to depend on the contiguous presentation of conditioned and unconditioned stimulus. However, what it means to be contiguous has not been rigorously defined. Here we examine the empirical bases for these beliefs and suggest an alternative view based on the hypothesis that learning about the temporal relationships between events determines the speed of emergence, vigor and form of conditioned behavior. This temporal learning occurs very rapidly and prior to the appearance of the anticipatory response. The temporal relations are learned even when no anticipatory response is evoked. The speed with which an anticipatory response emerges is proportional to the informativeness of the predictive cue (CS) regarding the rate of occurrence of the predicted event (US). This analysis gives an account of what we mean by "temporal pairing" and is in accord with the data on speed of acquisition and basic findings in the cue competition literature. In this account, learning depends on perceiving and encoding temporal regularities rather than stimulus contiguities.