Infrared light emitting diodes (IR LED) are often used in illumination of mazes to evaluate behaviors that are reflective of the animal’s natural nocturnal activities. In animals such as rats and mice that display an aversion for bright lights (Keller, 1941; Misslin, Belzung & Vogel, 2009), standard laboratory lighting (white light) may be deterrent in observing intrinsic and naturalistic behaviors during task performances. Rama, Capi, Tanaka, and Kawahara (2016) observed rats switch from spatial memory in lighting environments to previously learned sequences of actions in dark environments when evaluated in their novel infrared LED-lined Y-Maze. Thus, behavioral differences under different lighting conditions is a factor that needs to considered during behavioral investigations. Additionally, IR LEDs improve contrast for better detection during video recording and tracking (see tracking and recording system Noldus EthoVision XT and ANY-maze Behavior Tracking Software) of task performances under low-light or completely dark conditions without disturbing the animals or the task.
Infrared sensors, commonly composed of IR LED and IR detector pairs, are added to mazes to improve automatization of the task. The underlying principle is based on interruption of the infrared beam produced by the LED by movements or activity of the subjects in the maze. These interruptions can be used for scoring or triggering an event. Events can include an automatic closure of guillotine doors in a Radial Arm Maze such as that used by Dubreuil and colleagues (Dubreuil, Tixier, Dutrieux, & Edeline, 2003). The sensors can be effectively used for introduction of task delays in mazes such as the T-Maze and the Y-maze, and detection of behaviors such as pellet intake (Zhang, Kobayashi, Goto, & Itohara, 2018) during tasks. The opportunity to place the sensors in desired locations in a maze proves to be of great benefit in complex mazes. Segmentation of the monitored spaces in apparatuses such as an Open-Field eases the scoring of behaviors. Use of precision IR sensors in apparatuses such as Rotarod greatly reduces measurement errors and can also be used for real-time detection of positions in apparatuses like the rodent Running Wheel (Chen et al., 2015). The use of IR sensors reduces experimenter involvement, thereby reducing the influence of such interactions on task performances.
In nociception research involving thermal stimuli, the use of infrared heating elements is quite useful. Thermal sensitivity tests such as the Hargreaves Plantar (Hargreaves, Dubner, Brown, Flores, & Joris, 1988) and the Tail Flick test benefit from the use of IR heat stimulus that can also be used for scoring of behaviors in combination with IR sensors. The intensity of the heat stimulus can also be easily controlled.
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- Rama, E., Capi, G., Tanaka, N., & Kawahara, S. (2016). Rats Spatial Learning in an Novel Elevated Y-Maze. 5th Annual International Conference on Cognitive and Behavioral Psychology.
- Zhang, Q., Kobayashi, Y., Goto, H., & Itohara, S. (2018). An Automated T-maze Based Apparatus and Protocol for Analyzing Delay- and Effort-based Decision Making in Free Moving Rodents. Journal of Visualized Experiments, (138). doi:10.3791/57895