Blink reflexes inposterior fossa lesions

SUMMARY Blink reflexes obtained by electrical stimulation of the supraorbital nerve andelectromyographic recording of the orbicularis oculi muscle proved useful as a preliminarymethod in diagnosis of lesions of the brainstem andthe fifth andseventh cranial nerves, andindifferentiating intrinsic lesions of the brainstem from extrinsic ones. It was noted that RI andR2reflexes were different in the twotypes oflesions. Electric stimulation of the supraorbital nerve andelectromyographical registration of the orbitalmuscle of the eyelids give two distinct responses(Kugelberg, 1952; Rushworth, 1962), a first earlyresponse (RI), ipsilateral to the stimulated side,relatively constant in duration and shape, syn-chronous, andwhichonlyveryslowly dies outwithrepetitive stimulation; and a second late response(R2), which corresponds to clinically observableblinking. Thelatter response is variablein durationand morphology of the action potential. It isasynchronous and rapidly habituates, disappearingbilaterally. RI has a latency of