Corneal reflex responses to mechanical and electrical stimuli in coma and narcotic analgesia in humans

The corneal reflex, a bilateral eye-blink, can be elicited in humans either by mechanical or electrical corneal stimulation. Both in comatose patients and in normal subjects injected with the opiate fentanyl, the electrically-evoked corneal reflex was more suppressed than the mechanically-evoked reflex. We propose that the mechanical input yields a reflex more resistant to depression of the corticoreticular drive and to narcotic analgesia, because it exploits temporal summation at central synapses, whereas the electrical input exploits spatial summation.