Clinical and preclinical studies that have examined the neurobiology of persistent fear memory in posttraumatic stress disorder (PTSD) have focused on the medial prefrontal cortex, hippocampus, and amygdala. Sensory systems, the periaqueductal gray (PAG), and midline thalamic nuclei have been implicated in fear and extinction memory, but whether…

Studies on the behavioral mechanisms underlying contextual fear conditioning (CFC) have demonstrated the importance of preshock context exposure in the formation of aversive context memories. However, there has been comparatively little investigation of the effects of context exposure immediately after the shock. Some models predict that…

Pairs of rats foraged in trials either together or separately in an open field apparatus for pellets hidden in discreet locations in a 5 x 5 matrix. Trial duration was either 1 or 4 min. The tendency to choose locations that had earlier been visited by another rat was examined by comparing the choices made in the presence and absence of the other…

Estrogen has been shown to have a strong modulatory influence on several types of cognition in both women and female rodents. Latent inhibition is a task in which pre-exposure to a neutral stimulus, such as a tone, later impedes the association of that stimulus with a particular consequence, such as a shock. Previous work from our lab demonstrates…

Two experiments examined temporally based changes in the conditioned magazine-entries of rats when a target food pellet arrived at a fixed time before the termination of a conditioned stimulus. Both experiments found that increasing the rate of intertrial pellets systematically interfered with the rate of acquisition. When intertrial pellets were…

Grace and McLean (2006) proposed a decision model for acquisition of choice in concurrent chains which assumes that after reinforcement in a terminal link, subjects make a discrimination whether the preceding reinforcer delay was short or long relative to a criterion. Their model was subsequently extended by Christensen and Grace (2008, 2009a,…

This paper presents evidence of extinction, spontaneous recovery and renewal in a conditioned preferences paradigm based on taste-taste associations. More specifically, in three experiments rats exposed to a simultaneous compound of citric acid-saccharin solution showed a preference for the citric solution when the preference was measured with a…

It is well known that emotions participate in the regulation of social behaviors and that the emotion displayed by a conspecific influences the behavior of other animals. In its simplest form, empathy can be characterized as the capacity to be affected by and/or share the emotional state of another. However, to date, relatively little is known…

Increased emotionality is a characteristic of human adolescence, but its animal models are limited. Here we report that generalization of auditory conditioned fear between a conditional stimulus (CS+) and a novel auditory stimulus is stronger in 4-5-wk-old mice (juveniles) than in their 9-10-wk-old counterparts (adults), whereas nonassociative…

Two groups of 10 male rats were trained to nose poke for food pellets at four alternatives that provided differing rates of pellet delivery on aperiodic schedules. After a fixed number of pellets had been delivered, 5, 10 or 20 in different conditions of the experiment, a 10-s blackout occurred, and the locations of the differing rates of pellet…

A. Redish et al. (2007) proposed a reinforcement learning model of context-dependent learning and extinction in conditioning experiments, using the idea of "state classification" to categorize new observations into states. In the current article, the authors propose an interpretation of this idea in terms of normative statistical inference. They…

Research has shown that animals and humans habituate on a variety of behavioral and physiological responses to repeated presentations of food cues, and habituation is related to amount of food consumed and cessation of eating. The purpose of this article is to provide an overview of experimental paradigms used to study habituation, integrate a…

Long-term memory formation is regulated by many distinct molecular mechanisms that control gene expression. An emerging model for effecting a stable, coordinated pattern of gene transcription involves epigenetic tagging through modifications of histones or DNA. In this study, we investigated the regulation of histone phosphorylation in the…

Three mechanisms can explain second-order conditioning: (1) The second-order conditioned stimulus (CS2) could activate a representation of the first-order conditioned stimulus (CS1), thereby provoking the conditioned response (CR); The CS2 could enter into an excitatory association with either (2) the representation governing the CR, or (3) with a…

The present study explored whether a similar phenomenon to stimulus over-selectivity occurred in rats, in the hope of establishing a non-human model for the autism. Rats were serially presented with two-15 seconds, two-element compound stimuli prior to the delivery of food, in an appetitive classical conditioning procedure. Each compound stimulus…