A novel method for detecting licking behavior during recording of electrophysiological signals from the brain

We have developed a novel method for detecting licking at a fluid well that is compatible with behavioral neurophysiology. This method uses off-the-shelf fiber optic technology to introduce a light beam through the fluid-air interface of a fluid bolus in a well. A self-adjusting optical sensor detects licking as disturbances in the amplified light surface within the interface when the fluid is disturbed. The proper configuration of fluid well and fiber optics will reliably detect licking and introduce no artifacts into simultaneous high-impedance recordings of extracellular neural activity. This method is also compatible with delivery of multiple fluids to the same well. Unlike present methods of detecting licking in neurophysiological experiments, our approach does not involve the passage of current or capacitance changes in which the animal forms part of a circuit, nor does it require movement of the licking apparatus or any other response beyond the actual licking of the fluid. As a result, noise artifacts in the unit recordings do not occur, and the sensor is highly resistant to artifacts caused by exploration or licking at the fluid well in the absence of liquid. We present neural recording data from units in the nucleus accumbens demonstrating these properties of the lick detector.