Figure 1.

Basic firing properties of facial motoneurons. (A) A representative example of the phasic firing activity of an identified orbicularis oculi facial motoneuron recorded in a behaving cat during the presentation of an air puff to the ipsilateral cornea. From top to bottom are illustrated the stimulus presentation, the partial intracellular recording, and eyelid acceleration and position. Below is presented the power spectrum of lid acceleration trace with a dominant peak at 20 Hz, and in the inset is illustrated an average of the neuronal recording to show the duration of post-spike hyperpolarization (≈50 ms). (B) Tonic firing activity of the same motoneuron during classical conditioning in a well-trained cat. In the illustrated example, for a better observation of the typical firing during the eyelid conditioned response (CR), the air puff was not presented. Note that eyelid acceleration was only half that during the reflex response and that in this case motoneuron activity was mainly related to eyelid position, but the dominant oscillation of the CR and motoneuron hyperpolarization were similar to the profiles presented during the corneal reflex. Illustrated recordings are reproduced with permission and adapted from Trigo et al. (1999b).