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Citation Information : Acta Neurobiologiae Experimentalis. Volume 76, Issue 2, Pages 87-97, DOI: https://doi.org/10.21307/ane-2017-008
License : (CC BY 4.0)
Received Date : 13-November-2015 / Accepted: 24-April-2016 / Published Online: 25-July-2017
Fear-conditioning is one of the most widely used paradigms in attempts to unravel the processes and mechanisms underlying learning and plasticity. In most Pavlovian conditioning paradigms an auditory stimulus is used as the conditioned stimulus (CS), but conditioning to a tactile CS can also be accomplished. The whisker-to-barrel tactile system in mice offers a convenient way to investigate the brain pathways and mechanisms of learning and plasticity of the cerebral cortex. To support the claim that an animal learns during conditioning sessions and that the resulting plastic changes are associative in nature, objective measures of behavior are necessary. Multiple types of conditioned responses can develop depending on the training situation, CS and unconditioned stimulus (UCS) characteristics. These include physiological responses such as salivation, heart rate, and galvanic skin reaction, and also behavioral responses such as startle reflex potentiation or suppression of an ongoing behavior. When studying learning with the whisker system in behaving mice, stimulation of individual whiskers in a well-controlled manner may require animal restraint, which has the disadvantage of limiting the observation of potential behavioral responses. Stimulation of whiskers in a neck-restraining apparatus evokes head movements. When whisker stimulation (CS) is paired with an aversive UCS during conditioning, the number of head movements decrease in the course of the training. This reaction, called minifreezing, resembles the frequently used behavioral measure known as the freezing response. However, this is only applicable for freely moving animals. This article will review experimental evidence confirming that minifreezing is a relevant index of association formation between the neutral CS and aversive UCS.