Fear Incubation Using an Extended Fear-Conditioning Protocol for Rats

César Acevedo-Triana; Javier L. Rico; Leonardo A. Ortega; Melissa  Andrea N. Cardenas; Fernando P. Cardenas; Manuel J. Rojas; Juan Carlos Forigua-Vargas; Julián Cifuentes; Camilo Hurtado-Parrado

doi:10.3791/60537

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Method Article

Fear Incubation Using an Extended Fear-Conditioning Protocol for Rats

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DOI:

10.3791/60537

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August 22nd, 2020

César Acevedo-Triana¹^,⁶ , Javier L. Rico² , Leonardo A. Ortega² , Melissa Andrea N. Cardenas³ , Fernando P. Cardenas³ , Manuel J. Rojas⁴ , Juan Carlos Forigua-Vargas² , Julián Cifuentes² , Camilo Hurtado-Parrado²^,⁵

¹School of Psychology, Universidad Pedagógica y Tecnológica de Colombia, ²Animal Behavior Laboratory, Fundación Universitaria Konrad Lorenz, ³Department of Psychology, Universidad de Los Andes, ⁴School of Veterinary Medicine, Animal Health Department, Universidad Nacional de Colombia, ⁵Department of Psychology, Troy University, ⁶Department of Neurobiology, University of Alabama at Birmingham

Summary

We describe an extended fear-conditioning protocol that produces overtraining and fear incubation in rats. This protocol entails a single training session with 25 tone-shock pairings (i.e., overtraining) and a comparison of conditioned freezing responses during context and cue tests 48 h (short-term) and 6 weeks (long-term) after training.

Abstract

Emotional memory has been primarily studied with fear-conditioning paradigms. Fear conditioning is a form of learning through which individuals learn the relationships between aversive events and otherwise neutral stimuli. The most-widely utilized procedures for studying emotional memories entail fear conditioning in rats. In these tasks, the unconditioned stimulus (US) is a footshock presented once or several times across single or several sessions, and the conditioned response (CR) is freezing. In a version of these procedures, called cued fear conditioning, a tone (conditioned stimulus, CS) is paired with footshocks (US) during the training phase. During the first test, animals are exposed to the same context in which training took place, and freezing responses are tested in the absence of footshocks and tones (i.e., a context test). During the second test, freezing is measured when the context is changed (e.g., by manipulating the smell and walls of the experimental chamber) and the tone is presented in the absence of footshocks (i.e., a cue test). Most cued fear conditioning procedures entail few tone-shock pairings (e.g., 1-3 trials in a single session). There is a growing interest in less common versions involving an extensive number of pairings (i.e., overtraining) related to the long-lasting effect called fear incubation (i.e., fear responses increase over time without further exposure to aversive events or conditioned stimuli). Extended fear-conditioning tasks have been key to the understanding of fear incubation’s behavioral and neurobiological aspects, including its relationship with other psychological phenomena (e.g., post-traumatic stress disorder). Here, we describe an extended fear-conditioning protocol that produces overtraining and fear incubation in rats. This protocol entails a single training session with 25 tone-shock pairings (i.e., overtraining) and a comparison of conditioned freezing responses during context and cue tests 48 h (short-term) and 6 weeks (long-term) after training.

Introduction

Memory is a psychological process encompassing different phases: information acquisition, consolidation (allows for the stability of acquired information), and retrieval (evidence for the consolidation process)¹. During the consolidation phase, the establishment of new synaptic connections and modification of pre-existing connections occur. This suggests the necessity for a period of time during which molecular and physiological events responsible for these changes occur¹^,². These physiological or molecular changes vary whether the retrieved events are emotionally charged or not (i.e., ....