Timing of omitted events: an analysis of temporal control of inhibitory behavior

The sometimes competing retrieval and Van Hamme & Wasserman models predict the selective role of within-compound associations in retrospective revaluation

The correlation between blocking and within-compound memory is stronger when compound training occurs before elemental training (i.e., backward blocking) than when the phases are reversed (i.e., forward blocking; Melchers et al., 2004, 2006). This trial order effect is often interpreted as problematic for performance-focused models that assume a critical role for within-compound associations in both retrospective revaluation and traditional cue competition. The present manuscript revisits this issue using a computational modeling approach. The fit of sometimes competing retrieval (SOCR; Stout & Miller, 2007) was compared to the fit of an acquisition-focused model of retrospective revaluation and cue competition. These simulations reveal that SOCR explains this trial order effect in some situations based on its use of local error reduction.

A Rescorla-Wagner drift-diffusion model of conditioning and timing

Computational models of classical conditioning have made significant contributions to the theoretic understanding of associative learning, yet they still struggle when the temporal aspects of conditioning are taken into account. Interval timing models have contributed a rich variety of time representations and provided accurate predictions for the timing of responses, but they usually have little to say about associative learning. In this article we present a unified model of conditioning and timing that is based on the influential Rescorla-Wagner conditioning model and the more recently developed Timing Drift-Diffusion model. We test the model by simulating 10 experimental phenomena and show that it can provide an adequate account for 8, and a partial account for the other 2. We argue that the model can account for more phenomena in the chosen set than these other similar in scope models: CSC-TD, MS-TD, Learning to Time and Modular Theory. A comparison and analysis of the mechanisms in these models is provided, with a focus on the types of time representation and associative learning rule used.

Molecular mechanisms underlying formation of long-term reward memories and extinction memories in the honeybee (Apis mellifera)

The honeybee (Apis mellifera) has long served as an invertebrate model organism for reward learning and memory research. Its capacity for learning and memory formation is rooted in the ecological need to efficiently collect nectar and pollen during summer to ensure survival of the hive during winter. Foraging bees learn to associate a flower's characteristic features with a reward in a way that resembles olfactory appetitive classical conditioning, a learning paradigm that is used to study mechanisms underlying learning and memory formation in the honeybee. Due to a plethora of studies on appetitive classical conditioning and phenomena related to it, the honeybee is one of the best characterized invertebrate model organisms from a learning psychological point of view. Moreover, classical conditioning and associated behavioral phenomena are surprisingly similar in honeybees and vertebrates, suggesting a convergence of underlying neuronal processes, including the molecular mechanisms that contribute to them. Here I review current thinking on the molecular mechanisms underlying long-term memory (LTM) formation in honeybees following classical conditioning and extinction, demonstrating that an in-depth analysis of the molecular mechanisms of classical conditioning in honeybees might add to our understanding of associative learning in honeybees and vertebrates.

Temporal maps in appetitive Pavlovian conditioning

Previous research suggests animals may integrate temporal information into mental representations, or temporal maps. We examined the parameters under which animals integrate temporal information in three appetitive conditioning experiments. In Experiment 1 the temporal relationship between 2 auditory cues was established during sensory preconditioning (SPC). Subsequently, rats were given first order conditioning (FOC) with one of the cues. Results showed integration of the order of cues between the SPC and FOC training phases. In subsequent experiments we tested the hypothesis that quantitative temporal information can be integrated across phases. In Experiment 2, SPC of two short auditory cues superimposed on a longer auditory cue was followed by FOC of either one of the short cues, or of the long cue at different times in the cue. Contrary to our predictions we did not find evidence of integration of temporal information across the phases of the experiment and instead responding to the SPC cues in Experiment 2 appeared to be dominated by generalization from the FOC cues. In Experiment 3 shorter auditory cues were superimposed on a longer duration light cue but with asynchronous onset and offset of the superimposed cues. There is some evidence consistent with the hypothesis that quantitative discrimination of whether reward should be expected during the early or later parts of a cue could be integrated across experiences. However, the pattern of responding within cues was not indicative of integration of quantitative temporal information. Generalization of expected times of reward during FOC seems to be the dominant determinant of within-cue response patterns in these experiments. Consequently, while we clearly demonstrated the integration of temporal order in the modulation of this dominant pattern we did not find strong evidence of integration of precise quantitative temporal information. This article is part of a Special Issue entitled: Associative and Temporal Learning.

Generalization of Conditioned Fear and Obsessive-Compulsive Traits

Generalization of conditioned fear refers to the transfer of the conditioned fear response to stimuli that resemble the original conditioned stimulus. Overgeneralization of conditioned fear has been associated with panic disorder and generalized anxiety disorder and may be relevant to obsessive-compulsive (OC) symptoms as well. This study represents the first attempt to determine the degree to which individuals with high versus low OC traits over generalize conditioned fear. We hypothesized that the high OC individuals, particularly those characterized by overestimation of threat, would show overgeneralization of conditioned fear compared to controls as measured by behavioral and psychophysiological (fear-potentiated startle) measures. The results of this study show an interaction between the high and low Threat Estimation groups as measured by the Obsessive Beliefs Questionnaire, which suggests that those who have a tendency to overestimate threat show overgeneralization of conditioned fear. This finding suggests that the relation between OC symptoms and overgeneralization of conditioned fear may be specific to the high threat estimation component of OC symptoms.

Olfactory interference during inhibitory backward pairing in honey bees

BACKGROUND

Restrained worker honey bees are a valuable model for studying the behavioral and neural bases of olfactory plasticity. The proboscis extension response (PER; the proboscis is the mouthpart of honey bees) is released in response to sucrose stimulation. If sucrose stimulation is preceded one or a few times by an odor (forward pairing), the bee will form a memory for this association, and subsequent presentations of the odor alone are sufficient to elicit the PER. However, backward pairing between the two stimuli (sucrose, then odor) has not been studied to any great extent in bees, although the vertebrate literature indicates that it elicits a form of inhibitory plasticity.

METHODOLOGY/PRINCIPAL FINDINGS

If hungry bees are fed with sucrose, they will release a long lasting PER; however, this PER can be interrupted if an odor is presented 15 seconds (but not 7 or 30 seconds) after the sucrose (backward pairing). We refer to this previously unreported process as olfactory interference. Bees receiving this 15 second backward pairing show reduced performance after a subsequent single forward pairing (excitatory conditioning) trial. Analysis of the results supported a relationship between olfactory interference and a form of backward pairing-induced inhibitory learning/memory. Injecting the drug cimetidine into the deutocerebrum impaired olfactory interference.

CONCLUSIONS/SIGNIFICANCE

Olfactory interference depends on the associative link between odor and PER, rather than between odor and sucrose. Furthermore, pairing an odor with sucrose can lead either to association of this odor to PER or to the inhibition of PER by this odor. Olfactory interference may provide insight into processes that gate how excitatory and inhibitory memories for odor-PER associations are formed.

Determinants of cue interactions

In a Pavlovian conditioning situation, there are many training variables that may affect responding to a conditioned stimulus (CS), such as contiguity, contingency, and the presence of other CSs. This review describes recent experiments that show that some manipulations that usually decrease responding to a CS may have the opposite effect when they are combined with other normally pernicious manipulations. A theoretical framework that explains these so-called counteraction effects is provided. The apparent boundary conditions on the effects and limitations of the theory are discussed.