Licking behavior in the rat: measurement and situational control of licking frequency

Lick sensors are versatile instruments that are routinely used in behavioral and neuroscience research involving fluid ingestion in the rat. There are three different types of sensors: electrical, optical and force sensors. They differ in the exact moment of activation during the tongue protrusion/retraction cycle. Precautions in the use of each type of sensor are discussed. Adequate lick detection requires restriction of access to the water source to the tongue of the animal. It appears that drinking configurations that fulfill this task may affect the modal licking frequency. Increasing the amount of tongue travel that is needed to reach the drinking tube or water surface, decreases the licking frequency. The licking frequency can be manipulated between about 7.5 and 4 Hz. Therefore, if 'invariant' licking/lapping frequencies are observed, this is not so much the manifestation of a rigid output of a central pattern generator, but more the consequence of similarity in the effects of the employed drinking configurations. Applications of lick sensors in behavioral and neuroscience research are briefly discussed.