Role of proprioception in the control of lid position during reflex and conditioned blink responses in the alert behaving cat

The contribution of the orbicularis oculi muscle to the determination of li d position, and the putative role of eyelid proprioception in the control o f reflex and conditioned eye blinks, were studied in alert behaving cats. U pper lid movements and the electromyographic activity of the orbicularis oc uli muscle were recorded during reflexively evoked blinks and during the cl assical conditioning of the eyelid response. Blinks were evoked by air puff s, flashes and electrical stimulation of the supraorbitary branch of the tr igeminal nerve. Eyelid responses were conditioned with a trace classical co nditioning paradigm consisting of a short, weak air puff, followed 250 ms l ater by a long, strong air puff. Orbicularis oculi muscle activation during reflex blinks was independent of lid position and was not modified by the presence of weights acting in the upward or downward directions. Local anes thesia of the supraorbital nerve reduced blinks evoked by air puffs applied to the lower jaw, but did not affect flash-evoked blinks. No relationship was established between initial lid position and the first downward compone nt of conditioned eyelid responses. In contrast, initial lid position was r elated to the first upward component of the same conditioned response. It is concluded that orbicularis oculi motor units receive no feedback prop rioceptive signals from the eyelid, other than those coming from cutaneous receptors, and that lid position is determined by the activity of the levat or palpebrae superioris muscle. The lack of sensory information about lid p osition in facial motoneurons probably has some functional implications on the central control of cognitive and emotional facial expressions. (C) 1999 IBRO. published by Elsevier Science Ltd.