Behavioural tests based on the spontaneous recognition paradigm have been used extensively for examining the memory capacity of rodents. By exploiting their innate preference to investigate novel stimuli, inferences can be drawn about the perceived familiarity of encountered objects. Olfaction is the dominant sense used by mice to navigate their environment, yet these tests are often conducted using visual objects. By employing odors, one can reduce the high level of variability commonly observed between subjects. In this paper, we describe a protocol for assessing context-dependent odor memory by probing spatial and temporal associations separately or in conjunction with each other. We also detail a context-independent novel odor recognition protocol. These tests offer a simple and effective method for measuring odor memory in rodents using cheap and easily obtained materials.
When presented with a novel and familiar odor, mice behaviorally express memory for the familiar odor by spending a greater proportion of time investigating the unknown stimulus (Ennaceur and Delacour, 1988). Previously encountered odors can also instigate an increase in investigation if it is found in a novel position in space or temporal sequence (Mitchell and Laiacona, 1998; Eacott and Norman, 2004; Dere et al., 2005; Hunsaker et al., 2008; Barker et al., 2017; Aqrabawi and Kim, 2018). This sensitivity to the contextual information associated with an odor can be useful for evaluating different aspects of memory which may manifest from unique neural substrates. This is particularly useful when investigating with animal models of memory disorders where one form of memory is affected to a greater extent. Notably, none of the behavioral paradigms require extensive training and can be easily modified to suit experimental needs.
Materials and Reagents
Woodchip bedding
3 cm wide x 1 cm high aluminum cups
Ziploc bags
Ground herbs and spices (Club House brand, although others are acceptable)
Equipment
Acrylic glass cages (50 cm x 25 cm x 20 cm and 50 cm x 50 cm x 20 cm) (Figure 1)
Video Camera
Figure 1. Adaptable apparatus. Photograph of an acrylic glass cage (50 cm x 25 cm x 20 cm) used for Procedures A-D.