This work is supported by a Baylor University Research Council grant and from a research grant from the Epilepsy Foundation.

The mice used in the following experiment were generated and housed at Baylor University at an ambient temperature of 22 &#176;C, with a 14&#160;hr light and 10&#160;hr dark (20:00 to 6:00 hr) diurnal cycle. The mice were given ad libitum access to food and water. All procedures to the mice were in compliance with the National Institutes of Health Guidelines for the Care and Use of Laboratory Animals and the animal protocol was approved by Baylor University Animal Care and Use Committee.
Overview
The trace conditioned fear task is based on procedures described by Wiltgen and colleagues9.
1. Preparation of Equipment
The fear conditioning apparatus chamber (26 cm x 22 cm x 18 cm) consists of two sides that are acrylic, two sides that are metal, and a grid floor bottom which is used to deliver a mild foot shock. The testing chamber is housed in a sound attenuated chamber. The chamber is also light tight to prevent outside light from influencing the motion detection software.
<ol>
	<li>Calibrate the shock levels, light levels, and sound intensity levels for the testing chamber. Measure the background level of the testing chamber. The background noise in this chamber is 65 dB. Use a sound meter to measure this level. The meter should be set to 70 dB, set to C, and to detection setting slow.
	<ol>
		<li>Calibrate the shock level to 0.5 mA. Use an external calibration device to correctly calibrate the shock level (see Materials Table). The internal measurement of the shock generator is not accurate. The shock generator administers a scrambled shock which cannot be accurately measured by a standard amp meter.</li>
		<li>Place one lead on one of the grid bars and place the other lead 3 or 4 bars over. Use the shock generator to administer the shock. Adjust the shock level until the correct level is achieved. Do this for each fear conditioning chamber.</li>
		<li>Close the door to the chamber when measuring the light level of the chamber. Calibrate the light level to approximately 1.0. This is a number specific to the FreezeFrame software used in this experiment. An external light meter will read this as 2 lux. The light level can be adjusted by moving the location of the house light or by adjusting the condenser of the lens. Make sure to tighten the adjusting screws for the lens after adjusting.</li>
		<li>Calibrate the sound decibel level to 85 dB. Use an external decibel meter inside the testing cage to calibrate the decibel level (see Materials Table). The sound presented will be a 2,700 Hz tone. Note: If using mice older than 6 months old it may be better to use white noise since older mice can have hearing deficits .</li>
	</ol>
	</li>
	<li>After the apparatus is ready take the subjects to a separate holding room. Note: Do not house the mouse in the same room as the testing room.</li>
	<li>Label the tail of the mice that will be tested in order of testing. It is best to reduce excessive handling before testing. Alternatively, the tails can be labeled the day before the experiment to reduce handling stress. After the mice have been labeled allow them to acclimate to the room for 30 min. Have extra clean cages for housing the mice after testing is completed.</li>
</ol>
2. Trace Conditioning&#160;Day 1
<ol>
	<li>Remove each mouse from the cage and place them in individual cages for transport to the fear conditioning chamber. Use clean bedding for each cage. Place a sticky note on the transfer cage to keep the order of mice testing correct. Note: If the mice are singly housed then they can be transported in their home cage.</li>
	<li>Place the mouse in the testing chamber and close the door. Start the software program.</li>
	<li>On the training day, allow the mice to explore the chamber for 3 min. The software then presents a 20 sec tone (85 dB, 2,700 Hz) to the animal. After a trace period of 20 sec a mild shock (2 sec, 0.5 mA) is administered to the animal.</li>
	<li>Record the reaction of the subject to confirm that they received the aversive stimuli by viewing the video. A 200 sec inter-trial interval separates the 5 conditioning trials. Each trial consists of a 20 sec tone followed by a 20 sec delay then a shock.</li>
	<li>After testing is completed allow the animal to remain in the testing chamber for 1 min before removing it from the testing cage.</li>
	<li>Place the animal back in the transfer cage and return it to its home cage. If there are additional mice in their home cage then individually house the mouse until all mice complete testing. This will reduce the stress to the other mice that have not been tested. An alternative solution would be to singly house all mice one week prior to testing to reduce the influence of continuously removing mice from one cage.</li>
	<li>Clean the testing chamber with 30% isopropanol after each animal is tested.</li>
	<li>Repeat steps 2.2-2.7 for all mice in the testing cohort.</li>
	<li>Return all mice to their colony room after the last mouse in the cohort has been tested.</li>
</ol>
3. Trace Fear Conditioning Day 2: Trace Memory Testing
<ol>
	<li>Trace memory testing will occur on day 2. In this protocol there are 3 tone presentations. Place the mice in a new context for the trace conditioning test.</li>
	<li>Prepare the software to run a program with a 2 min baseline period followed by three 20&#160;sec tone presentations. There is s a 220&#160;sec ITI between each tone presentation.</li>
	<li>For the new context condition, place clear acrylic inserts on the floor of the chamber to alter the shape, texture, and color of the conditioning chamber.</li>
	<li>Change the odor in the chamber by placing vanilla extract in a weigh boat under the floor insert.</li>
	<li>Clean the chamber with 70% ethanol instead of 30% isopropanol. Note: This will help to create a novel context.</li>
	<li>Bring the mice to the holding room and relabel their tails for testing if necessary.</li>
	<li>Prepare novel context transfer cages by replacing the bedding with shredded paper. Note: This will help in creating a novel context.</li>
	<li>Place the mice in the testing chamber then start the program. Clean the chamber with 70% ethanol after testing is completed.</li>
	<li>Return the mice to their home cage after the trace conditioning is completed. Return all mice to their colony room when all mice have been tested.</li>
</ol>
4. Trace Fear Conditioning Day 3: Contextual Memory Testing
<ol>
	<li>On the third day contextual conditioning is conducted. Prepare the software to run a program to record freezing behavior for 8 min.</li>
	<li>Clean the chamber with 30% isopropanol before testing and after testing each mouse. The context should be identical to that of day 1. The transfer cages should be the same as in day 1.</li>
	<li>Bring mice to the holding room and label their tails for testing.</li>
	<li>Place each mouse in the testing chamber then start the program. Clean the chamber with 30% isopropanol after testing is completed.</li>
	<li>Return all mice to their colony room when completed.</li>
</ol>

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The authors have nothing to disclose.

There have been several studies that have elucidated the neural circuitry that underlies trace fear conditioning. Trace fear conditioning is believed to involve the CA1 of the hippocampus12-14. There is also evidence that the medial prefrontal cortex (mPFC) plays a large role in trace eye-blink conditioning15, and the mPFC has been found to be involved in trace fear conditioning. One study found that mPFC neurons provide sustained activity during the trace period, thus providing a structure that can...

In fear conditioning a neutral stimulus (NS) is paired with an aversive unconditioned stimulus (US). The NS is normally a tone and becomes a conditioned stimulus (CS) through repeated pairings with the US. The CS can then elicit a conditioned response (CR), such as freezing, in the absence of the aversive US. A commonly used fear conditioning protocol is delay conditioning. In this protocol the onset of the NS and the US is contiguous or with some overlap in stimulus presentation. Even though delay fear conditioning is one of the most commonly used types of temporal associative conditioning, there are several other types of associative conditioning temporal arrangements: simultaneous conditioning, backward conditioning, and trace conditioning1. In trace fear conditioning there is a stimulus-free interval between the NS and the US of several seconds resulting in a &#34;trace&#34; period.
Several studies have reported deficits in trace fear conditioning when neurotoxic lesions are produced in the structures that input into the hippocampus2-5 or when pharmacological agents are used to block receptor function in the hippocampus. Lesion to the hippocampus results in deficits in trace conditioning and contextual conditioning, but does not impair delay fear conditioning8. There are several benefits to using trace fear conditioning. The fear conditioning protocol can be achieved over a three-day testing period and allows for hippocampal-dependent memory that is not spatially dependent. Trace fear conditioning can be used as a complementary test to the Morris water maze, novel object recognition test, or other maze tests in investigating hippocampal-dependent memory.

<table border="0" cellpadding="0" cellspacing="0" width="741">
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	<tbody>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">FreezeFrame</td>
			<td style="width:143px;">Coulbourn</td>
			<td style="width:119px;"></td>
			<td style="width:263px;"></td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:216px;">30% Isopropanol</td>
			<td style="width:143px;"></td>
			<td style="width:119px;"></td>
			<td style="width:263px;">Purchase 90% isopropanol and dilute it down to 30%</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">70% Ethanol</td>
			<td style="width:143px;"></td>
			<td style="width:119px;"></td>
			<td style="width:263px;"></td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:216px;">Amp-meter</td>
			<td style="width:143px;">Med-Associates</td>
			<td style="width:119px;">ENV-420</td>
			<td style="width:263px;">Windows XP, Vista, and 7 Compatible (32-bit only)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Digital Sound Level Meter</td>
			<td style="width:143px;"></td>
			<td style="width:119px;">33-2055</td>
			<td style="width:263px;"></td>
		</tr>
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			<td height="41" style="height:41px;width:216px;">Vanilla Extract</td>
			<td style="width:143px;">McCormick Pure Vanilla Extract</td>
			<td style="width:119px;"></td>
			<td style="width:263px;"></td>
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			<td height="21" style="height:21px;width:216px;">Sticky Notes</td>
			<td style="width:143px;">Post-it</td>
			<td style="width:119px;"></td>
			<td style="width:263px;">3X3 inch</td>
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trace fear conditioning in mice

In this experiment we present a technique to measure learning and memory. In the trace fear conditioning protocol presented here there are five pairings between a neutral stimulus and an unconditioned stimulus. There is a 20 sec trace period that separates each conditioning trial. On the following day freezing is measured during presentation of the conditioned stimulus (CS) and trace period. On the third day there is an 8 min test to measure contextual memory. The representative results are from mice that were presented with the aversive unconditioned stimulus (shock) compared to mice that received the tone presentations without the unconditioned stimulus. Trace fear conditioning has been successfully used to detect subtle learning and memory deficits and enhancements in mice that are not found with other fear conditioning methods. This type of fear conditioning is believed to be dependent upon connections between the medial prefrontal cortex and the hippocampus. One current controversy is whether this method is believed to be amygdala-independent. Therefore, other fear conditioning testing is needed to examine amygdala-dependent learning and memory effects, such as through the delay fear conditioning.

For the representative results we present data from control C57BL/6J adult mice that received the neutral stimulus pairings with the unconditioned stimulus (shock condition) compared to mice that received the neutral stimulus but did not receive the unconditioned stimulus (no shock condition). It is important to run this condition when first setting up this behavioral test to determine whether the protocol has been performed correctly.
The data in Figure 1 represent the traini...

Watch this Scientific Journal Video about Trace Fear Conditioning in Mice at JoVE.com

Trace Fear Conditioning in Mice

In the following experiment we describe a protocol for trace fear conditioning in mice. This type of associative memory includes a trace period that separates the neutral stimulus and the unconditioned stimulus.

In this experiment we present a technique to measure learning and memory. In the trace fear conditioning protocol presented here there are five pairings ...

Research

JoVE Journal

Behavior

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Video: Trace Fear Conditioning in Mice

Contextual and Cued Fear Conditioning Test Using a Video Analyzing System in Mice

The contextual and cued fear conditioning test is one of the behavioral tests that assesses the ability of mice to learn and remember an association between environmental cues and aversive experiences. In this test, mice are placed into a conditioning chamber and are given parings of a conditioned stimulus (an auditory cue) and an aversive unconditioned stimulus (an electric footshock). After a delay time, the mice are exposed to the same conditioning chamber and a differently shaped chamber with presentation of the auditory cue. Freezing behavior during the test is measured as an index of fear memory. To analyze the behavior automatically, we have developed a video analyzing system using the ImageFZ application software program, which is available as a free download at http://www.mouse-phenotype.org/. Here, to show the details of our protocol, we demonstrate our procedure for the contextual and cued fear conditioning test in C57BL/6J mice using the ImageFZ system. In addition, we validated our protocol and the video analyzing system performance by comparing freezing time measured by the ImageFZ system or a photobeam-based computer measurement system with that scored by a human observer. As shown in our representative results, the data obtained by ImageFZ were similar to those analyzed by a human observer, indicating that the behavioral analysis using the ImageFZ system is highly reliable. The present movie article provides detailed information regarding the test procedures and will promote understanding of the experimental situation.

This article presents a protocol for a contextual and cued fear conditioning test using a video analyzing system to assess fear learning and memory in mice.

The contextual and cued fear conditioning test is one of the behavioral tests that assesses the ability of mice to learn and remember an association ...

Disrupting Reconsolidation of Fear Memory in Humans by a Noradrenergic &#946;-Blocker

The basic design used in our human fear-conditioning studies on disrupting reconsolidation includes testing over different phases across three consecutive days. On day 1 - the fear acquisition phase, healthy participants are exposed to a series of picture presentations. One picture stimulus (CS1+) is repeatedly paired with an aversive electric stimulus (US), resulting in the acquisition of a fear association, whereas another picture stimulus (CS2-) is never followed by an US. On day 2 - the memory reactivation phase, the participants are re-exposed to the conditioned stimulus without the US (CS1-), which typically triggers a conditioned fear response. After the memory reactivation we administer an oral dose of 40 mg of propranolol HCl, a &#946;-adrenergic receptor antagonist that indirectly targets the protein synthesis required for reconsolidation by inhibiting the noradrenaline-stimulated CREB phosphorylation. On day 3 - the test phase, the participants are again exposed to the unreinforced conditioned stimuli (CS1- and CS2-) in order to measure the fear-reducing effect of the manipulation. This retention test is followed by an extinction procedure and the presentation of situational triggers to test for the return of fear. Potentiation of the eye blink startle reflex is measured as an index for conditioned fear responding. Declarative knowledge of the fear association is measured through online US expectancy ratings during each CS presentation. In contrast to extinction learning, disrupting reconsolidation targets the original fear memory thereby preventing the return of fear. Although the clinical applications are still in their infancy, disrupting reconsolidation of fear memory seems to be a promising new technique with the prospect to persistently dampen the expression of fear memory in patients suffering from anxiety disorders and other psychiatric disorders.

Disrupting Reconsolidation of Fear Memory in Humans by a Noradrenergic &amp;#946;-Blocker

Disrupting reconsolidation is a promising approach to dampen the behavioral expression of fear memory in patients with anxiety disorders or posttraumatic stress disorder. In a series of human fear conditioning studies we showed that disrupting reconsolidation by the noradrenergic &#946;-blocker propranolol is very effective in erasing conditioned fear responding.

The basic design used in our human fear-conditioning studies on disrupting reconsolidation includes testing over different phases across three consecutive ...

Protocol for Studying Extinction of Conditioned Fear in Naturally Cycling Female Rats

Extinction of conditioned fear has been extensively studied in male rodents. Recently, there have been an increasing number of studies indicating that neural mechanisms for certain behavioral tasks and response behaviors are different in females and males. Using females in research studies can represent a challenge because of the variation of gonadal hormones during their estrous cycle. This protocol describes well-established procedures that are useful in investigating the role of estrogen in fear extinction memory consolidation in female rats. Phase of the estrous cycle and exogenous estrogen administration prior to extinction training can influence extinction recall 24 hr later. The vaginal swabbing technique for estrous phase identification described here aids the examination and manipulation of naturally cycling gonadal hormones. The use of this basic rodent model may further delineate the mechanisms by which estrogen can modulate fear extinction memory in females.

Gonadal hormones such as estrogen modulate memory formation in a number of experimental paradigms including fear extinction memory. This protocol describes a set of methods for investigating the influence of gonadal hormones specifically during extinction in naturally cycling females, including estrous cycle monitoring and exogenous estrogen administration.

Extinction of conditioned fear has been extensively studied in male rodents. Recently, there have been an increasing number of studies indicating that ...

Quantifying Social Motivation in Mice Using Operant Conditioning

In this protocol, social motivation is measured in mice through a pair of operant conditioning paradigms. To conduct the experiments, two-chambered shuttle boxes were equipped with two operant levers (left and right) and a food receptacle in one chamber, which was then divided from the second chamber by an automated guillotine door covered by a wire grid. Different stimulus mice, rotated across testing days, served as a social stimulus behind the wire grid, and were only visible following the opening of the guillotine door. Test mice were trained to lever press in order to open the door and gain access to the stimulus partner for 15 sec. The number of lever presses required to obtain the social reward progressively increased on a fixed schedule of 3. Testing sessions ended after test mice stopped lever pressing for 5 consecutive minutes. The last reinforced ratio or breakpoint can be used as a quantitative measure of social motivation. For the second paradigm, test mice were trained to discriminate between left and right lever presses in order to obtain either a food reward or the social reward. Mice were rewarded for every 3 presses of each respective lever. The number of food and social rewards can be compared as a measurement of the value placed upon each reward. The ratio of each reward type can also be compared between mouse strains and the change in this ratio can be monitored within testing sessions to measure satiation with a given reward type. Both of these operant conditioning paradigms are highly useful for the quantification of social motivation in mouse models of autism and other disorders of social behavior.

This article describes a new protocol for the quantitative measurement of social motivation in mice using operant conditioning for a social reward. The protocol is useful for the measurement of social motivation in mouse models of autism and other disorders of social behavior.

In this protocol, social motivation is measured in mice through a pair of operant conditioning paradigms. To conduct the experiments, two-chambered ...

Whisker-signaled Eyeblink Classical Conditioning in Head-fixed Mice

Eyeblink conditioning is a common paradigm for investigating the neural mechanisms underlying learning and memory. To better utilize the extensive repertoire of scientific techniques available to study learning and memory at the cellular level, it is ideal to have a stable cranial platform. Because mice do not readily tolerate restraint, they are usually trained while moving about freely in a chamber. Conditioned stimulus (CS) and unconditioned stimulus (US) information are delivered and eyeblink responses recorded via a tether connected to the mouse's head. In the head-fixed apparatus presented here, mice are allowed to run as they desire while their heads are secured to facilitate experimentation. Reliable conditioning of the eyeblink response is obtained with this training apparatus, which allows for the delivery of whisker stimulation as the CS, a periorbital electrical shock as the US, and analysis of electromyographic (EMG) activity from the eyelid to detect blink responses.

The preparation presented here for whisker-signaled eyeblink conditioning in head-fixed mice precisely stimulates specific whiskers while allowing mice to ambulate on a cylindrical treadmill. A whisker stimulation conditioned stimulus (CS) paired with a periorbital shock unconditioned stimulus (US) results in reliable associative learning on this apparatus.

Eyeblink conditioning is a common paradigm for investigating the neural mechanisms underlying learning and memory. To better utilize the extensive ...

Reducing State Anxiety Using Working Memory Maintenance

The purpose of this protocol is to explain how to examine the relationship between working memory processes and anxiety by combining the Sternberg Working Memory (WM) and the threat of shock paradigms. In the Sternberg WM paradigm, subjects are required to maintain a series of letters in the WM for a brief interval and respond by identifying whether the position of a given letter in the series matches a numerical prompt. In the threat of shock paradigm, subjects are exposed to alternating blocks where they are either at risk of receiving unpredictable presentations of a mild electric shock or are safe from the shock. Anxiety is probed throughout the safe and threat blocks using the acoustic startle reflex, which is potentiated under threat (Anxiety-Potentiated Startle (APS)). By conducting the Sternberg WM paradigm during the threat of shock and probing the startle response during either the WM maintenance interval or the intertrial interval, it is possible to determine the effect of WM maintenance on APS.

This protocol demonstrates how to measure anxiety-potentiated startle during the Sternberg Working Memory paradigm.

The purpose of this protocol is to explain how to examine the relationship between working memory processes and anxiety by combining the Sternberg Working ...

Classical Short-Delay Eyeblink Conditioning in One-Year-Old Children

Classical eyeblink conditioning (EBC) refers to the learned association between a conditioned stimulus (an auditory tone) and an unconditioned stimulus (a puff of air to the cornea). Eyeblink conditioning is often used experimentally to detect abnormalities in cerebellar-dependent learning and memory that underlies this type of associative learning. While experiments in adults and older children are relatively simple to administer using commercial equipment, eyeblink conditioning in infants is more challenging due to their poor compliance, which makes correct positioning of the equipment difficult. To achieve conditioning in one-year-old infants, a custom-made or an adapted commercial system can be used to deliver the air puff to the infant's cornea. The main challenge lies in successfully detecting and classifying the behavioral responses. We report that automated blink detection methods are unreliable in this population, and that conditioning experiments should be analyzed using frame-by-frame analysis of supplementary video camera recordings. This method can be applied to study developmental changes in eyeblink conditioning and to examine whether this paradigm can detect children with neurological disorders.

This protocol describes an eyeblink conditioning paradigm appropriate for experiments with one-year-old infants. Commercial or custom-made equipment can be used to deliver the stimuli, and data collection and analysis should be performed on the video recordings.

Classical eyeblink conditioning (EBC) refers to the learned association between a conditioned stimulus (an auditory tone) and an unconditioned stimulus (a ...

Stress-Enhanced Fear Learning, a Robust Rodent Model of Post-Traumatic Stress Disorder

Fear behaviors are important for survival, but disproportionately high levels of fear can increase the vulnerability for developing psychiatric disorders such as post-traumatic stress disorder (PTSD). To understand the biological mechanisms of fear dysregulation in PTSD, it is important to start with a valid animal model of the disorder. This protocol describes the methodology required to conduct stress-enhanced fear learning (SEFL) experiments, a preclinical model of PTSD, in both rats and mice. SEFL was developed to recapitulate critical aspects of PTSD, including long-term sensitization of fear learning caused by an acute stressor. SEFL uses aspects of Pavlovian fear conditioning but produces a distinct and robust sensitized fear response far greater than normal conditional fear responses. The trauma procedure involves placing a rodent in a conditioning chamber and administering 15 unsignaled shocks randomly distributed over 90 minutes (for rat experiments; for mouse experiments, 10 unsignaled shocks randomly distributed over 60 minutes are used). On day 2, rodents are placed in a novel conditioning context where they receive a single shock; then, on day 3 they are placed back in the same context as on day 2 and tested for changes in freezing levels. Rodents that previously received the trauma display enhanced levels of freezing on the test day compared to those that received no shocks on the first day. Thus, with this model, a single highly stressful experience (the trauma) produces extreme fear of the stimuli associated with the traumatic event.

Here we describe the detailed methodology required to conduct stress-enhanced fear learning (SEFL) experiments, a preclinical model of post-traumatic stress disorder, in both rats and mice. The model utilizes aspects of Pavlovian fear conditioning and freezing as an index of enhanced fear in rodents.

Fear behaviors are important for survival, but disproportionately high levels of fear can increase the vulnerability for developing psychiatric disorders ...

Visual Classical Conditioning in Wood Ants

Several species of insects have become model systems for studying learning and memory formation. Although many studies focus on freely moving animals, studies implementing classical conditioning paradigms with harnessed insects have been important for investigating the exact cues that individuals learn and the neural mechanisms underlying learning and memory formation. Here we present a protocol for evoking visual associative learning in wood ants through classical conditioning. In this paradigm, ants are harnessed and presented with a visual cue (a blue cardboard), the conditional stimulus (CS), paired with an appetitive sugar reward, the unconditional stimulus (US). Ants perform a Maxilla-Labium Extension Reflex (MaLER), the unconditional response (UR), which can be used as a readout for learning. Training consists of 10 trials, separated by a 5-minute intertrial interval (ITI). Ants are also tested for memory retention 10 minutes or 1 hour after training. This protocol has the potential to allow researchers to analyze, in a precise and controlled manner, the details of visual memory formation and the neural basis of learning and memory formation in wood ants.

We present a protocol for the classical conditioning of harnessed ants that permits researchers to study visual learning and memory formation at a level of analysis not possible with freely moving individuals.

Several species of insects have become model systems for studying learning and memory formation. Although many studies focus on freely moving animals, ...

Fear Incubation Using an Extended Fear-Conditioning Protocol for Rats

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&#8217;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.

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.

Emotional memory has been primarily studied with fear-conditioning paradigms. Fear conditioning is a form of learning through which individuals learn the ...